src/pulsecore/source-output.c

/***
  This file is part of PulseAudio.

  Copyright 2004-2006 Lennart Poettering

  PulseAudio is free software; you can redistribute it and/or modify
  it under the terms of the GNU Lesser General Public License as published
  by the Free Software Foundation; either version 2.1 of the License,
  or (at your option) any later version.

  PulseAudio is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with PulseAudio; if not, see <http://www.gnu.org/licenses/>.
***/

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <pulse/utf8.h>
#include <pulse/xmalloc.h>
#include <pulse/util.h>
#include <pulse/internal.h>
#include <pulse/timeval.h>

#include <pulsecore/core-format.h>
#include <pulsecore/mix.h>
#include <pulsecore/stream-util.h>
#include <pulsecore/core-subscribe.h>
#include <pulsecore/log.h>
#include <pulsecore/namereg.h>
#include <pulsecore/core-util.h>

#include "source-output.h"

#define MEMBLOCKQ_MAXLENGTH (32*1024*1024)

PA_DEFINE_PUBLIC_CLASS(pa_source_output, pa_msgobject);

static void source_output_free(pa_object* mo);
static void set_real_ratio(pa_source_output *o, const pa_cvolume *v);

pa_source_output_new_data* pa_source_output_new_data_init(pa_source_output_new_data *data) {
    pa_assert(data);

    pa_zero(*data);
    data->resample_method = PA_RESAMPLER_INVALID;
    data->proplist = pa_proplist_new();
    data->volume_writable = true;

    return data;
}

void pa_source_output_new_data_set_sample_spec(pa_source_output_new_data *data, const pa_sample_spec *spec) {
    pa_assert(data);

    if ((data->sample_spec_is_set = !!spec))
        data->sample_spec = *spec;
}

void pa_source_output_new_data_set_channel_map(pa_source_output_new_data *data, const pa_channel_map *map) {
    pa_assert(data);

    if ((data->channel_map_is_set = !!map))
        data->channel_map = *map;
}

bool pa_source_output_new_data_is_passthrough(pa_source_output_new_data *data) {
    pa_assert(data);

    if (PA_LIKELY(data->format) && PA_UNLIKELY(!pa_format_info_is_pcm(data->format)))
        return true;

    if (PA_UNLIKELY(data->flags & PA_SOURCE_OUTPUT_PASSTHROUGH))
        return true;

    return false;
}

void pa_source_output_new_data_set_volume(pa_source_output_new_data *data, const pa_cvolume *volume) {
    pa_assert(data);
    pa_assert(data->volume_writable);

    if ((data->volume_is_set = !!volume))
        data->volume = *volume;
}

void pa_source_output_new_data_apply_volume_factor(pa_source_output_new_data *data, const pa_cvolume *volume_factor) {
    pa_assert(data);
    pa_assert(volume_factor);

    if (data->volume_factor_is_set)
        pa_sw_cvolume_multiply(&data->volume_factor, &data->volume_factor, volume_factor);
    else {
        data->volume_factor_is_set = true;
        data->volume_factor = *volume_factor;
    }
}

void pa_source_output_new_data_apply_volume_factor_source(pa_source_output_new_data *data, const pa_cvolume *volume_factor) {
    pa_assert(data);
    pa_assert(volume_factor);

    if (data->volume_factor_source_is_set)
        pa_sw_cvolume_multiply(&data->volume_factor_source, &data->volume_factor_source, volume_factor);
    else {
        data->volume_factor_source_is_set = true;
        data->volume_factor_source = *volume_factor;
    }
}

void pa_source_output_new_data_set_muted(pa_source_output_new_data *data, bool mute) {
    pa_assert(data);

    data->muted_is_set = true;
    data->muted = mute;
}

bool pa_source_output_new_data_set_source(pa_source_output_new_data *data, pa_source *s, bool save,
                                          bool requested_by_application) {
    bool ret = true;
    pa_idxset *formats = NULL;

    pa_assert(data);
    pa_assert(s);

    if (!data->req_formats) {
        /* We're not working with the extended API */
        data->source = s;
        if (save) {
            pa_xfree(data->preferred_source);
            data->preferred_source = pa_xstrdup(s->name);
        }
        data->source_requested_by_application = requested_by_application;
    } else {
        /* Extended API: let's see if this source supports the formats the client would like */
        formats = pa_source_check_formats(s, data->req_formats);

        if (formats && !pa_idxset_isempty(formats)) {
            /* Source supports at least one of the requested formats */
            data->source = s;
            if (save) {
                pa_xfree(data->preferred_source);
                data->preferred_source = pa_xstrdup(s->name);
            }
            data->source_requested_by_application = requested_by_application;
            if (data->nego_formats)
                pa_idxset_free(data->nego_formats, (pa_free_cb_t) pa_format_info_free);
            data->nego_formats = formats;
        } else {
            /* Source doesn't support any of the formats requested by the client */
            if (formats)
                pa_idxset_free(formats, (pa_free_cb_t) pa_format_info_free);
            ret = false;
        }
    }

    return ret;
}

bool pa_source_output_new_data_set_formats(pa_source_output_new_data *data, pa_idxset *formats) {
    pa_assert(data);
    pa_assert(formats);

    if (data->req_formats)
        pa_idxset_free(data->req_formats, (pa_free_cb_t) pa_format_info_free);

    data->req_formats = formats;

    if (data->source) {
        /* Trigger format negotiation */
        return pa_source_output_new_data_set_source(data, data->source, (data->preferred_source != NULL),
                                                    data->source_requested_by_application);
    }

    return true;
}

void pa_source_output_new_data_done(pa_source_output_new_data *data) {
    pa_assert(data);

    if (data->req_formats)
        pa_idxset_free(data->req_formats, (pa_free_cb_t) pa_format_info_free);

    if (data->nego_formats)
        pa_idxset_free(data->nego_formats, (pa_free_cb_t) pa_format_info_free);

    if (data->format)
        pa_format_info_free(data->format);

    if (data->preferred_source)
        pa_xfree(data->preferred_source);

    pa_proplist_free(data->proplist);
}

/* Called from main context */
static void reset_callbacks(pa_source_output *o) {
    pa_assert(o);

    o->push = NULL;
    o->process_rewind = NULL;
    o->update_max_rewind = NULL;
    o->update_source_requested_latency = NULL;
    o->update_source_latency_range = NULL;
    o->update_source_fixed_latency = NULL;
    o->attach = NULL;
    o->detach = NULL;
    o->suspend = NULL;
    o->suspend_within_thread = NULL;
    o->moving = NULL;
    o->kill = NULL;
    o->get_latency = NULL;
    o->state_change = NULL;
    o->may_move_to = NULL;
    o->send_event = NULL;
    o->volume_changed = NULL;
    o->mute_changed = NULL;
}

/* Called from main context */
int pa_source_output_new(
        pa_source_output**_o,
        pa_core *core,
        pa_source_output_new_data *data) {

    pa_source_output *o;
    pa_resampler *resampler = NULL;
    char st[PA_SAMPLE_SPEC_SNPRINT_MAX], cm[PA_CHANNEL_MAP_SNPRINT_MAX], fmt[PA_FORMAT_INFO_SNPRINT_MAX];
    pa_channel_map volume_map;
    int r;
    char *pt;
    size_t resampler_history;

    pa_assert(_o);
    pa_assert(core);
    pa_assert(data);
    pa_assert_ctl_context();

    if (data->client)
        pa_proplist_update(data->proplist, PA_UPDATE_MERGE, data->client->proplist);

    if (data->destination_source && (data->destination_source->flags & PA_SOURCE_SHARE_VOLUME_WITH_MASTER))
        data->volume_writable = false;

    if (!data->req_formats) {
        /* From this point on, we want to work only with formats, and get back
         * to using the sample spec and channel map after all decisions w.r.t.
         * routing are complete. */
        pa_format_info *f;
        pa_idxset *formats;

        f = pa_format_info_from_sample_spec2(&data->sample_spec, data->channel_map_is_set ? &data->channel_map : NULL,
                                             !(data->flags & PA_SOURCE_OUTPUT_FIX_FORMAT),
                                             !(data->flags & PA_SOURCE_OUTPUT_FIX_RATE),
                                             !(data->flags & PA_SOURCE_OUTPUT_FIX_CHANNELS));
        if (!f)
            return -PA_ERR_INVALID;

        formats = pa_idxset_new(NULL, NULL);
        pa_idxset_put(formats, f, NULL);
        pa_source_output_new_data_set_formats(data, formats);
    }

    if ((r = pa_hook_fire(&core->hooks[PA_CORE_HOOK_SOURCE_OUTPUT_NEW], data)) < 0)
        return r;

    pa_return_val_if_fail(!data->driver || pa_utf8_valid(data->driver), -PA_ERR_INVALID);

    if (!data->source) {
        pa_source *source;

        if (data->direct_on_input) {
            source = data->direct_on_input->sink->monitor_source;
            pa_return_val_if_fail(source, -PA_ERR_INVALID);
        } else {
            source = pa_namereg_get(core, NULL, PA_NAMEREG_SOURCE);
            pa_return_val_if_fail(source, -PA_ERR_NOENTITY);
        }

        pa_source_output_new_data_set_source(data, source, false, false);
    }

    /* If something didn't pick a format for us, pick the top-most format since
     * we assume this is sorted in priority order */
    if (!data->format && data->nego_formats && !pa_idxset_isempty(data->nego_formats))
        data->format = pa_format_info_copy(pa_idxset_first(data->nego_formats, NULL));

    if (PA_LIKELY(data->format)) {
        /* We know that data->source is set, because data->format has been set.
         * data->format is set after a successful format negotiation, and that
         * can't happen before data->source has been set. */
        pa_assert(data->source);

        pa_log_debug("Negotiated format: %s", pa_format_info_snprint(fmt, sizeof(fmt), data->format));
    } else {
        pa_format_info *format;
        uint32_t idx;

        pa_log_info("Source does not support any requested format:");
        PA_IDXSET_FOREACH(format, data->req_formats, idx)
            pa_log_info(" -- %s", pa_format_info_snprint(fmt, sizeof(fmt), format));

        return -PA_ERR_NOTSUPPORTED;
    }

    pa_return_val_if_fail(PA_SOURCE_IS_LINKED(data->source->state), -PA_ERR_BADSTATE);
    pa_return_val_if_fail(!data->direct_on_input || data->direct_on_input->sink == data->source->monitor_of, -PA_ERR_INVALID);

    /* Routing is done. We have a source and a format. */

    if (data->volume_is_set && !pa_source_output_new_data_is_passthrough(data)) {
        /* If volume is set, we need to save the original data->channel_map,
         * so that we can remap the volume from the original channel map to the
         * final channel map of the stream in case data->channel_map gets
         * modified in pa_format_info_to_sample_spec2(). */
        r = pa_stream_get_volume_channel_map(&data->volume, data->channel_map_is_set ? &data->channel_map : NULL, data->format, &volume_map);
        if (r < 0)
            return r;
    } else {
        /* Initialize volume_map to invalid state. We check the state later to
         * determine if volume remapping is needed. */
        pa_channel_map_init(&volume_map);
    }

    /* Now populate the sample spec and channel map according to the final
     * format that we've negotiated */
    r = pa_format_info_to_sample_spec2(data->format, &data->sample_spec, &data->channel_map, &data->source->sample_spec,
                                       &data->source->channel_map);
    if (r < 0)
        return r;

    /* Don't restore (or save) stream volume for passthrough streams and
     * prevent attenuation/gain */
    if (pa_source_output_new_data_is_passthrough(data)) {
        data->volume_is_set = true;
        pa_cvolume_reset(&data->volume, data->sample_spec.channels);
        data->volume_is_absolute = true;
        data->save_volume = false;
    }

    if (!data->volume_is_set) {
        pa_cvolume_reset(&data->volume, data->sample_spec.channels);
        data->volume_is_absolute = false;
        data->save_volume = false;
    }

    if (!data->volume_writable)
        data->save_volume = false;

    if (pa_channel_map_valid(&volume_map))
        /* The original volume channel map may be different than the final
         * stream channel map, so remapping may be needed. */
        pa_cvolume_remap(&data->volume, &volume_map, &data->channel_map);

    if (!data->volume_factor_is_set)
        pa_cvolume_reset(&data->volume_factor, data->sample_spec.channels);

    pa_return_val_if_fail(pa_cvolume_compatible(&data->volume_factor, &data->sample_spec), -PA_ERR_INVALID);

    if (!data->volume_factor_source_is_set)
        pa_cvolume_reset(&data->volume_factor_source, data->source->sample_spec.channels);

    pa_return_val_if_fail(pa_cvolume_compatible(&data->volume_factor_source, &data->source->sample_spec), -PA_ERR_INVALID);

    if (!data->muted_is_set)
        data->muted = false;

    if (!(data->flags & PA_SOURCE_OUTPUT_VARIABLE_RATE) &&
        !pa_sample_spec_equal(&data->sample_spec, &data->source->sample_spec)) {
        /* try to change source format and rate. This is done before the FIXATE hook since
           module-suspend-on-idle can resume a source */

        pa_log_info("Trying to change sample spec");
        pa_source_reconfigure(data->source, &data->sample_spec, pa_source_output_new_data_is_passthrough(data));
    }

    if (pa_source_output_new_data_is_passthrough(data) &&
        !pa_sample_spec_equal(&data->sample_spec, &data->source->sample_spec)) {
        /* rate update failed, or other parts of sample spec didn't match */

        pa_log_debug("Could not update source sample spec to match passthrough stream");
        return -PA_ERR_NOTSUPPORTED;
    }

    if (data->resample_method == PA_RESAMPLER_INVALID)
        data->resample_method = core->resample_method;

    pa_return_val_if_fail(data->resample_method < PA_RESAMPLER_MAX, -PA_ERR_INVALID);

    if ((r = pa_hook_fire(&core->hooks[PA_CORE_HOOK_SOURCE_OUTPUT_FIXATE], data)) < 0)
        return r;

    if ((data->flags & PA_SOURCE_OUTPUT_NO_CREATE_ON_SUSPEND) &&
        data->source->state == PA_SOURCE_SUSPENDED) {
        pa_log("Failed to create source output: source is suspended.");
        return -PA_ERR_BADSTATE;
    }

    if (pa_idxset_size(data->source->outputs) >= PA_MAX_OUTPUTS_PER_SOURCE) {
        pa_log("Failed to create source output: too many outputs per source.");
        return -PA_ERR_TOOLARGE;
    }

    if ((data->flags & PA_SOURCE_OUTPUT_VARIABLE_RATE) ||
        !pa_sample_spec_equal(&data->sample_spec, &data->source->sample_spec) ||
        !pa_channel_map_equal(&data->channel_map, &data->source->channel_map)) {

        if (!pa_source_output_new_data_is_passthrough(data)) /* no resampler for passthrough content */
            if (!(resampler = pa_resampler_new(
                        core->mempool,
                        &data->source->sample_spec, &data->source->channel_map,
                        &data->sample_spec, &data->channel_map,
                        core->lfe_crossover_freq,
                        data->resample_method,
                        ((data->flags & PA_SOURCE_OUTPUT_VARIABLE_RATE) ? PA_RESAMPLER_VARIABLE_RATE : 0) |
                        ((data->flags & PA_SOURCE_OUTPUT_NO_REMAP) ? PA_RESAMPLER_NO_REMAP : 0) |
                        (core->disable_remixing || (data->flags & PA_SOURCE_OUTPUT_NO_REMIX) ? PA_RESAMPLER_NO_REMIX : 0) |
                        (core->remixing_use_all_sink_channels ? 0 : PA_RESAMPLER_NO_FILL_SINK) |
                        (core->remixing_produce_lfe ? PA_RESAMPLER_PRODUCE_LFE : 0) |
                        (core->remixing_consume_lfe ? PA_RESAMPLER_CONSUME_LFE : 0)))) {
                pa_log_warn("Unsupported resampling operation.");
                return -PA_ERR_NOTSUPPORTED;
            }
    }

    o = pa_msgobject_new(pa_source_output);
    o->parent.parent.free = source_output_free;
    o->parent.process_msg = pa_source_output_process_msg;

    o->core = core;
    o->state = PA_SOURCE_OUTPUT_INIT;
    o->flags = data->flags;
    o->proplist = pa_proplist_copy(data->proplist);
    o->driver = pa_xstrdup(pa_path_get_filename(data->driver));
    o->module = data->module;
    o->source = data->source;
    o->source_requested_by_application = data->source_requested_by_application;
    o->destination_source = data->destination_source;
    o->client = data->client;

    o->requested_resample_method = data->resample_method;
    o->actual_resample_method = resampler ? pa_resampler_get_method(resampler) : PA_RESAMPLER_INVALID;
    o->sample_spec = data->sample_spec;
    o->channel_map = data->channel_map;
    o->format = pa_format_info_copy(data->format);

    if (!data->volume_is_absolute && pa_source_flat_volume_enabled(o->source)) {
        pa_cvolume remapped;

        /* When the 'absolute' bool is not set then we'll treat the volume
         * as relative to the source volume even in flat volume mode */
        remapped = data->source->reference_volume;
        pa_cvolume_remap(&remapped, &data->source->channel_map, &data->channel_map);
        pa_sw_cvolume_multiply(&o->volume, &data->volume, &remapped);
    } else
        o->volume = data->volume;

    o->volume_factor = data->volume_factor;
    o->volume_factor_source = data->volume_factor_source;
    o->real_ratio = o->reference_ratio = data->volume;
    pa_cvolume_reset(&o->soft_volume, o->sample_spec.channels);
    pa_cvolume_reset(&o->real_ratio, o->sample_spec.channels);
    o->volume_writable = data->volume_writable;
    o->save_volume = data->save_volume;
    o->preferred_source = pa_xstrdup(data->preferred_source);
    o->save_muted = data->save_muted;

    o->muted = data->muted;

    o->direct_on_input = data->direct_on_input;

    reset_callbacks(o);
    o->userdata = NULL;

    o->thread_info.state = o->state;
    o->thread_info.attached = false;
    o->thread_info.sample_spec = o->sample_spec;
    o->thread_info.resampler = resampler;
    o->thread_info.soft_volume = o->soft_volume;
    o->thread_info.muted = o->muted;
    o->thread_info.requested_source_latency = (pa_usec_t) -1;
    o->thread_info.direct_on_input = o->direct_on_input;

    o->thread_info.delay_memblockq = pa_memblockq_new(
            "source output delay_memblockq",
            0,
            MEMBLOCKQ_MAXLENGTH,
            0,
            &o->source->sample_spec,
            0,
            1,
            0,
            &o->source->silence);

    resampler_history = (uint64_t) PA_RESAMPLER_MAX_DELAY_USEC * o->source->sample_spec.rate / PA_USEC_PER_SEC;
    resampler_history *= pa_frame_size(&o->source->sample_spec);

    pa_memblockq_set_maxrewind(o->thread_info.delay_memblockq, resampler_history + pa_source_get_max_rewind(o->source));

    pa_assert_se(pa_idxset_put(core->source_outputs, o, &o->index) == 0);
    pa_assert_se(pa_idxset_put(o->source->outputs, pa_source_output_ref(o), NULL) == 0);

    if (o->client)
        pa_assert_se(pa_idxset_put(o->client->source_outputs, o, NULL) >= 0);

    if (o->direct_on_input)
        pa_assert_se(pa_idxset_put(o->direct_on_input->direct_outputs, o, NULL) == 0);

    pt = pa_proplist_to_string_sep(o->proplist, "\n    ");
    pa_log_info("Created output %u \"%s\" on %s with sample spec %s and channel map %s\n    %s",
                o->index,
                pa_strnull(pa_proplist_gets(o->proplist, PA_PROP_MEDIA_NAME)),
                o->source->name,
                pa_sample_spec_snprint(st, sizeof(st), &o->sample_spec),
                pa_channel_map_snprint(cm, sizeof(cm), &o->channel_map),
                pt);
    pa_xfree(pt);

    /* Don't forget to call pa_source_output_put! */

    *_o = o;
    return 0;
}

/* Called from main context */
static void update_n_corked(pa_source_output *o, pa_source_output_state_t state) {
    pa_assert(o);
    pa_assert_ctl_context();

    if (!o->source)
        return;

    if (o->state == PA_SOURCE_OUTPUT_CORKED && state != PA_SOURCE_OUTPUT_CORKED)
        pa_assert_se(o->source->n_corked -- >= 1);
    else if (o->state != PA_SOURCE_OUTPUT_CORKED && state == PA_SOURCE_OUTPUT_CORKED)
        o->source->n_corked++;
}

/* Called from main context */
static void source_output_set_state(pa_source_output *o, pa_source_output_state_t state) {

    pa_assert(o);
    pa_assert_ctl_context();

    if (o->state == state)
        return;

    if (o->source) {
        if (o->state == PA_SOURCE_OUTPUT_CORKED && state == PA_SOURCE_OUTPUT_RUNNING && pa_source_used_by(o->source) == 0 &&
            !pa_sample_spec_equal(&o->sample_spec, &o->source->sample_spec)) {
            /* We were uncorked and the source was not playing anything -- let's try
             * to update the sample format and rate to avoid resampling */
            pa_source_reconfigure(o->source, &o->sample_spec, pa_source_output_is_passthrough(o));
        }

        pa_assert_se(pa_asyncmsgq_send(o->source->asyncmsgq, PA_MSGOBJECT(o), PA_SOURCE_OUTPUT_MESSAGE_SET_STATE, PA_UINT_TO_PTR(state), 0, NULL) == 0);
    } else
        /* If the source is not valid, pa_source_output_set_state_within_thread() must be called directly */
        pa_source_output_set_state_within_thread(o, state);

    update_n_corked(o, state);
    o->state = state;

    if (state != PA_SOURCE_OUTPUT_UNLINKED) {
        pa_hook_fire(&o->core->hooks[PA_CORE_HOOK_SOURCE_OUTPUT_STATE_CHANGED], o);

        if (PA_SOURCE_OUTPUT_IS_LINKED(state))
            pa_subscription_post(o->core, PA_SUBSCRIPTION_EVENT_SOURCE_OUTPUT|PA_SUBSCRIPTION_EVENT_CHANGE, o->index);
    }

    if (o->source)
        pa_source_update_status(o->source);
}

/* Called from main context */
void pa_source_output_unlink(pa_source_output*o) {
    bool linked;

    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();

    /* See pa_sink_unlink() for a couple of comments how this function
     * works */

    pa_source_output_ref(o);

    linked = PA_SOURCE_OUTPUT_IS_LINKED(o->state);

    if (linked)
        pa_hook_fire(&o->core->hooks[PA_CORE_HOOK_SOURCE_OUTPUT_UNLINK], o);

    if (o->direct_on_input)
        pa_idxset_remove_by_data(o->direct_on_input->direct_outputs, o, NULL);

    pa_idxset_remove_by_data(o->core->source_outputs, o, NULL);

    if (o->source)
        if (pa_idxset_remove_by_data(o->source->outputs, o, NULL))
            pa_source_output_unref(o);

    if (o->client)
        pa_idxset_remove_by_data(o->client->source_outputs, o, NULL);

    update_n_corked(o, PA_SOURCE_OUTPUT_UNLINKED);
    o->state = PA_SOURCE_OUTPUT_UNLINKED;

    if (linked && o->source) {
        if (pa_source_output_is_passthrough(o))
            pa_source_leave_passthrough(o->source);

        /* We might need to update the source's volume if we are in flat volume mode. */
        if (pa_source_flat_volume_enabled(o->source))
            pa_source_set_volume(o->source, NULL, false, false);

        if (o->source->asyncmsgq)
            pa_assert_se(pa_asyncmsgq_send(o->source->asyncmsgq, PA_MSGOBJECT(o->source), PA_SOURCE_MESSAGE_REMOVE_OUTPUT, o, 0, NULL) == 0);
    }

    reset_callbacks(o);

    if (o->source) {
        if (PA_SOURCE_IS_LINKED(o->source->state))
            pa_source_update_status(o->source);

        o->source = NULL;
    }

    if (linked) {
        pa_subscription_post(o->core, PA_SUBSCRIPTION_EVENT_SOURCE_OUTPUT|PA_SUBSCRIPTION_EVENT_REMOVE, o->index);
        pa_hook_fire(&o->core->hooks[PA_CORE_HOOK_SOURCE_OUTPUT_UNLINK_POST], o);
    }

    pa_core_maybe_vacuum(o->core);

    pa_source_output_unref(o);
}

/* Called from main context */
static void source_output_free(pa_object* mo) {
    pa_source_output *o = PA_SOURCE_OUTPUT(mo);

    pa_assert(o);
    pa_assert_ctl_context();
    pa_assert(pa_source_output_refcnt(o) == 0);
    pa_assert(!PA_SOURCE_OUTPUT_IS_LINKED(o->state));

    pa_log_info("Freeing output %u \"%s\"", o->index,
                o->proplist ? pa_strnull(pa_proplist_gets(o->proplist, PA_PROP_MEDIA_NAME)) : "");

    if (o->thread_info.delay_memblockq)
        pa_memblockq_free(o->thread_info.delay_memblockq);

    if (o->thread_info.resampler)
        pa_resampler_free(o->thread_info.resampler);

    if (o->format)
        pa_format_info_free(o->format);

    if (o->proplist)
        pa_proplist_free(o->proplist);

    if (o->preferred_source)
        pa_xfree(o->preferred_source);

    pa_xfree(o->driver);
    pa_xfree(o);
}

/* Called from main context */
void pa_source_output_put(pa_source_output *o) {
    pa_source_output_state_t state;

    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();

    pa_assert(o->state == PA_SOURCE_OUTPUT_INIT);

    /* The following fields must be initialized properly */
    pa_assert(o->push);
    pa_assert(o->kill);

    state = o->flags & PA_SOURCE_OUTPUT_START_CORKED ? PA_SOURCE_OUTPUT_CORKED : PA_SOURCE_OUTPUT_RUNNING;

    update_n_corked(o, state);
    o->state = state;

    /* We might need to update the source's volume if we are in flat volume mode. */
    if (pa_source_flat_volume_enabled(o->source))
        pa_source_set_volume(o->source, NULL, false, o->save_volume);
    else {
        if (o->destination_source && (o->destination_source->flags & PA_SOURCE_SHARE_VOLUME_WITH_MASTER)) {
            pa_assert(pa_cvolume_is_norm(&o->volume));
            pa_assert(pa_cvolume_is_norm(&o->reference_ratio));
        }

        set_real_ratio(o, &o->volume);
    }

    if (pa_source_output_is_passthrough(o))
        pa_source_enter_passthrough(o->source);

    o->thread_info.soft_volume = o->soft_volume;
    o->thread_info.muted = o->muted;

    pa_assert_se(pa_asyncmsgq_send(o->source->asyncmsgq, PA_MSGOBJECT(o->source), PA_SOURCE_MESSAGE_ADD_OUTPUT, o, 0, NULL) == 0);

    pa_subscription_post(o->core, PA_SUBSCRIPTION_EVENT_SOURCE_OUTPUT|PA_SUBSCRIPTION_EVENT_NEW, o->index);
    pa_hook_fire(&o->core->hooks[PA_CORE_HOOK_SOURCE_OUTPUT_PUT], o);

    pa_source_update_status(o->source);
}

/* Called from main context */
void pa_source_output_kill(pa_source_output*o) {
    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();
    pa_assert(PA_SOURCE_OUTPUT_IS_LINKED(o->state));

    o->kill(o);
}

/* Called from main context */
pa_usec_t pa_source_output_get_latency(pa_source_output *o, pa_usec_t *source_latency) {
    pa_usec_t r[2] = { 0, 0 };

    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();
    pa_assert(PA_SOURCE_OUTPUT_IS_LINKED(o->state));

    pa_assert_se(pa_asyncmsgq_send(o->source->asyncmsgq, PA_MSGOBJECT(o), PA_SOURCE_OUTPUT_MESSAGE_GET_LATENCY, r, 0, NULL) == 0);

    if (o->get_latency)
        r[0] += o->get_latency(o);

    if (source_latency)
        *source_latency = r[1];

    return r[0];
}

/* Called from thread context */
void pa_source_output_push(pa_source_output *o, const pa_memchunk *chunk) {
    bool need_volume_factor_source;
    bool volume_is_norm;
    size_t length;
    size_t limit, mbs = 0;

    pa_source_output_assert_ref(o);
    pa_source_output_assert_io_context(o);
    pa_assert(PA_SOURCE_OUTPUT_IS_LINKED(o->thread_info.state));
    pa_assert(chunk);
    pa_assert(pa_frame_aligned(chunk->length, &o->source->sample_spec));

    if (!o->push || o->thread_info.state == PA_SOURCE_OUTPUT_CORKED)
        return;

    pa_assert(o->thread_info.state == PA_SOURCE_OUTPUT_RUNNING);

    if (pa_memblockq_push(o->thread_info.delay_memblockq, chunk) < 0) {
        pa_log_debug("Delay queue overflow!");
        pa_memblockq_seek(o->thread_info.delay_memblockq, (int64_t) chunk->length, PA_SEEK_RELATIVE, true);
    }

    limit = o->process_rewind ? 0 : o->source->thread_info.max_rewind;

    volume_is_norm = pa_cvolume_is_norm(&o->thread_info.soft_volume) && !o->thread_info.muted;
    need_volume_factor_source = !pa_cvolume_is_norm(&o->volume_factor_source);

    if (limit > 0 && o->source->monitor_of) {
        pa_usec_t latency;
        size_t n;

        /* Hmm, check the latency for knowing how much of the buffered
         * data is actually still unplayed and might hence still
         * change. This is suboptimal. Ideally we'd have a call like
         * pa_sink_get_changeable_size() or so that tells us how much
         * of the queued data is actually still changeable. Hence
         * FIXME! */

        latency = pa_sink_get_latency_within_thread(o->source->monitor_of, false);

        n = pa_usec_to_bytes(latency, &o->source->sample_spec);

        if (n < limit)
            limit = n;
    }

    /* Implement the delay queue */
    while ((length = pa_memblockq_get_length(o->thread_info.delay_memblockq)) > limit) {
        pa_memchunk qchunk;
        bool nvfs = need_volume_factor_source;

        length -= limit;

        pa_assert_se(pa_memblockq_peek(o->thread_info.delay_memblockq, &qchunk) >= 0);

        if (qchunk.length > length)
            qchunk.length = length;

        pa_assert(qchunk.length > 0);

        /* It might be necessary to adjust the volume here */
        if (!volume_is_norm) {
            pa_memchunk_make_writable(&qchunk, 0);

            if (o->thread_info.muted) {
                pa_silence_memchunk(&qchunk, &o->source->sample_spec);
                nvfs = false;

            } else if (!o->thread_info.resampler && nvfs) {
                pa_cvolume v;

                /* If we don't need a resampler we can merge the
                 * post and the pre volume adjustment into one */

                pa_sw_cvolume_multiply(&v, &o->thread_info.soft_volume, &o->volume_factor_source);
                pa_volume_memchunk(&qchunk, &o->source->sample_spec, &v);
                nvfs = false;

            } else
                pa_volume_memchunk(&qchunk, &o->source->sample_spec, &o->thread_info.soft_volume);
        }

        if (nvfs) {
            pa_memchunk_make_writable(&qchunk, 0);
            pa_volume_memchunk(&qchunk, &o->source->sample_spec, &o->volume_factor_source);
        }

        if (!o->thread_info.resampler)
            o->push(o, &qchunk);
        else {
            pa_memchunk rchunk;

            if (mbs == 0)
                mbs = pa_resampler_max_block_size(o->thread_info.resampler);

            if (qchunk.length > mbs)
                qchunk.length = mbs;

            pa_resampler_run(o->thread_info.resampler, &qchunk, &rchunk);

            if (rchunk.length > 0)
                o->push(o, &rchunk);

            if (rchunk.memblock)
                pa_memblock_unref(rchunk.memblock);
        }

        pa_memblock_unref(qchunk.memblock);
        pa_memblockq_drop(o->thread_info.delay_memblockq, qchunk.length);
    }
}

/* Called from thread context */
void pa_source_output_process_rewind(pa_source_output *o, size_t nbytes /* in source sample spec */) {

    pa_source_output_assert_ref(o);
    pa_source_output_assert_io_context(o);
    pa_assert(PA_SOURCE_OUTPUT_IS_LINKED(o->thread_info.state));
    pa_assert(pa_frame_aligned(nbytes, &o->source->sample_spec));

    if (nbytes <= 0)
        return;

    if (o->process_rewind) {
        size_t source_output_nbytes;
        size_t length;

        /* The length of the memblockq may be non-zero if pa_source_output_rewind() is called twice
         * without pa_source_output_push() called in between. In that case, the resampler has already
         * been reset and we can skip that part. */
        length = pa_memblockq_get_length(o->thread_info.delay_memblockq);

        pa_memblockq_rewind(o->thread_info.delay_memblockq, nbytes);

        source_output_nbytes = pa_resampler_result(o->thread_info.resampler, nbytes);

        pa_log_debug("Have to rewind %lu bytes on implementor.", (unsigned long) source_output_nbytes);

        if (source_output_nbytes > 0)
            o->process_rewind(o, source_output_nbytes);

        if (o->thread_info.resampler && length == 0) {
            size_t resampler_bytes;

            /* Round down to full frames */
            resampler_bytes = (size_t) pa_resampler_get_delay(o->thread_info.resampler, false) * pa_frame_size(&o->source->sample_spec);
            if (resampler_bytes > 0)
                pa_memblockq_rewind(o->thread_info.delay_memblockq, resampler_bytes);

            pa_resampler_rewind(o->thread_info.resampler, source_output_nbytes, NULL, 0);
        }
    }

    pa_memblockq_seek(o->thread_info.delay_memblockq, - ((int64_t) nbytes), PA_SEEK_RELATIVE, true);
}

/* Called from thread context */
size_t pa_source_output_get_max_rewind(pa_source_output *o) {
    pa_source_output_assert_ref(o);
    pa_source_output_assert_io_context(o);

    return pa_resampler_result(o->thread_info.resampler, o->source->thread_info.max_rewind);
}

/* Called from thread context */
void pa_source_output_update_max_rewind(pa_source_output *o, size_t nbytes  /* in the source's sample spec */) {
    size_t resampler_history;

    pa_source_output_assert_ref(o);
    pa_source_output_assert_io_context(o);
    pa_assert(PA_SOURCE_OUTPUT_IS_LINKED(o->thread_info.state));
    pa_assert(pa_frame_aligned(nbytes, &o->source->sample_spec));

    resampler_history = (uint64_t) PA_RESAMPLER_MAX_DELAY_USEC * o->source->sample_spec.rate / PA_USEC_PER_SEC;
    resampler_history *= pa_frame_size(&o->source->sample_spec);

    pa_memblockq_set_maxrewind(o->thread_info.delay_memblockq, resampler_history + nbytes);

    if (o->update_max_rewind)
        o->update_max_rewind(o, pa_resampler_result(o->thread_info.resampler, nbytes));
}

/* Called from thread context */
pa_usec_t pa_source_output_set_requested_latency_within_thread(pa_source_output *o, pa_usec_t usec) {
    pa_source_output_assert_ref(o);
    pa_source_output_assert_io_context(o);

    if (!(o->source->flags & PA_SOURCE_DYNAMIC_LATENCY))
        usec = o->source->thread_info.fixed_latency;

    if (usec != (pa_usec_t) -1)
        usec = PA_CLAMP(usec, o->source->thread_info.min_latency, o->source->thread_info.max_latency);

    o->thread_info.requested_source_latency = usec;
    pa_source_invalidate_requested_latency(o->source, true);

    return usec;
}

/* Called from main context */
pa_usec_t pa_source_output_set_requested_latency(pa_source_output *o, pa_usec_t usec) {
    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();

    if (PA_SOURCE_OUTPUT_IS_LINKED(o->state) && o->source) {
        pa_assert_se(pa_asyncmsgq_send(o->source->asyncmsgq, PA_MSGOBJECT(o), PA_SOURCE_OUTPUT_MESSAGE_SET_REQUESTED_LATENCY, &usec, 0, NULL) == 0);
        return usec;
    }

    /* If this source output is not realized yet or is being moved, we
     * have to touch the thread info data directly */

    if (o->source) {
        if (!(o->source->flags & PA_SOURCE_DYNAMIC_LATENCY))
            usec = pa_source_get_fixed_latency(o->source);

        if (usec != (pa_usec_t) -1) {
            pa_usec_t min_latency, max_latency;
            pa_source_get_latency_range(o->source, &min_latency, &max_latency);
            usec = PA_CLAMP(usec, min_latency, max_latency);
        }
    }

    o->thread_info.requested_source_latency = usec;

    return usec;
}

/* Called from main context */
pa_usec_t pa_source_output_get_requested_latency(pa_source_output *o) {
    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();

    if (PA_SOURCE_OUTPUT_IS_LINKED(o->state) && o->source) {
        pa_usec_t usec = 0;
        pa_assert_se(pa_asyncmsgq_send(o->source->asyncmsgq, PA_MSGOBJECT(o), PA_SOURCE_OUTPUT_MESSAGE_GET_REQUESTED_LATENCY, &usec, 0, NULL) == 0);
        return usec;
    }

    /* If this source output is not realized yet or is being moved, we
     * have to touch the thread info data directly */

    return o->thread_info.requested_source_latency;
}

/* Called from main context */
void pa_source_output_set_volume(pa_source_output *o, const pa_cvolume *volume, bool save, bool absolute) {
    pa_cvolume v;

    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();
    pa_assert(PA_SOURCE_OUTPUT_IS_LINKED(o->state));
    pa_assert(volume);
    pa_assert(pa_cvolume_valid(volume));
    pa_assert(volume->channels == 1 || pa_cvolume_compatible(volume, &o->sample_spec));
    pa_assert(o->volume_writable);

    if (!absolute && pa_source_flat_volume_enabled(o->source)) {
        v = o->source->reference_volume;
        pa_cvolume_remap(&v, &o->source->channel_map, &o->channel_map);

        if (pa_cvolume_compatible(volume, &o->sample_spec))
            volume = pa_sw_cvolume_multiply(&v, &v, volume);
        else
            volume = pa_sw_cvolume_multiply_scalar(&v, &v, pa_cvolume_max(volume));
    } else {
        if (!pa_cvolume_compatible(volume, &o->sample_spec)) {
            v = o->volume;
            volume = pa_cvolume_scale(&v, pa_cvolume_max(volume));
        }
    }

    if (pa_cvolume_equal(volume, &o->volume)) {
        o->save_volume = o->save_volume || save;
        return;
    }

    pa_source_output_set_volume_direct(o, volume);
    o->save_volume = save;

    if (pa_source_flat_volume_enabled(o->source)) {
        /* We are in flat volume mode, so let's update all source input
         * volumes and update the flat volume of the source */

        pa_source_set_volume(o->source, NULL, true, save);

    } else {
        /* OK, we are in normal volume mode. The volume only affects
         * ourselves */
        set_real_ratio(o, volume);

        /* Copy the new soft_volume to the thread_info struct */
        pa_assert_se(pa_asyncmsgq_send(o->source->asyncmsgq, PA_MSGOBJECT(o), PA_SOURCE_OUTPUT_MESSAGE_SET_SOFT_VOLUME, NULL, 0, NULL) == 0);
    }

    /* The volume changed, let's tell people so */
    if (o->volume_changed)
        o->volume_changed(o);

    /* The virtual volume changed, let's tell people so */
    pa_subscription_post(o->core, PA_SUBSCRIPTION_EVENT_SOURCE_OUTPUT|PA_SUBSCRIPTION_EVENT_CHANGE, o->index);
}

/* Called from main context */
static void set_real_ratio(pa_source_output *o, const pa_cvolume *v) {
    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();
    pa_assert(PA_SOURCE_OUTPUT_IS_LINKED(o->state));
    pa_assert(!v || pa_cvolume_compatible(v, &o->sample_spec));

    /* This basically calculates:
     *
     * o->real_ratio := v
     * o->soft_volume := o->real_ratio * o->volume_factor */

    if (v)
        o->real_ratio = *v;
    else
        pa_cvolume_reset(&o->real_ratio, o->sample_spec.channels);

    pa_sw_cvolume_multiply(&o->soft_volume, &o->real_ratio, &o->volume_factor);
    /* We don't copy the data to the thread_info data. That's left for someone else to do */
}

/* Called from main or I/O context */
bool pa_source_output_is_passthrough(pa_source_output *o) {
    pa_source_output_assert_ref(o);

    if (PA_UNLIKELY(!pa_format_info_is_pcm(o->format)))
        return true;

    if (PA_UNLIKELY(o->flags & PA_SOURCE_OUTPUT_PASSTHROUGH))
        return true;

    return false;
}

/* Called from main context */
bool pa_source_output_is_volume_readable(pa_source_output *o) {
    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();

    return !pa_source_output_is_passthrough(o);
}

/* Called from main context */
pa_cvolume *pa_source_output_get_volume(pa_source_output *o, pa_cvolume *volume, bool absolute) {
    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();
    pa_assert(PA_SOURCE_OUTPUT_IS_LINKED(o->state));
    pa_assert(pa_source_output_is_volume_readable(o));

    if (absolute || !pa_source_flat_volume_enabled(o->source))
        *volume = o->volume;
    else
        *volume = o->reference_ratio;

    return volume;
}

/* Called from main context */
void pa_source_output_set_mute(pa_source_output *o, bool mute, bool save) {
    bool old_mute;

    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();
    pa_assert(PA_SOURCE_OUTPUT_IS_LINKED(o->state));

    old_mute = o->muted;

    if (mute == old_mute) {
        o->save_muted |= save;
        return;
    }

    o->muted = mute;
    pa_log_debug("The mute of source output %u changed from %s to %s.", o->index, pa_yes_no(old_mute), pa_yes_no(mute));

    o->save_muted = save;

    pa_assert_se(pa_asyncmsgq_send(o->source->asyncmsgq, PA_MSGOBJECT(o), PA_SOURCE_OUTPUT_MESSAGE_SET_SOFT_MUTE, NULL, 0, NULL) == 0);

    /* The mute status changed, let's tell people so */
    if (o->mute_changed)
        o->mute_changed(o);

    pa_subscription_post(o->core, PA_SUBSCRIPTION_EVENT_SOURCE_OUTPUT|PA_SUBSCRIPTION_EVENT_CHANGE, o->index);
    pa_hook_fire(&o->core->hooks[PA_CORE_HOOK_SOURCE_OUTPUT_MUTE_CHANGED], o);
}

void pa_source_output_set_property(pa_source_output *o, const char *key, const char *value) {
    char *old_value = NULL;
    const char *new_value;

    pa_assert(o);
    pa_assert(key);

    if (pa_proplist_contains(o->proplist, key)) {
        old_value = pa_xstrdup(pa_proplist_gets(o->proplist, key));
        if (value && old_value && pa_streq(value, old_value))
            goto finish;

        if (!old_value)
            old_value = pa_xstrdup("(data)");
    } else {
        if (!value)
            goto finish;

        old_value = pa_xstrdup("(unset)");
    }

    if (value) {
        pa_proplist_sets(o->proplist, key, value);
        new_value = value;
    } else {
        pa_proplist_unset(o->proplist, key);
        new_value = "(unset)";
    }

    if (PA_SOURCE_OUTPUT_IS_LINKED(o->state)) {
        pa_log_debug("Source output %u: proplist[%s]: %s -> %s", o->index, key, old_value, new_value);
        pa_hook_fire(&o->core->hooks[PA_CORE_HOOK_SOURCE_OUTPUT_PROPLIST_CHANGED], o);
        pa_subscription_post(o->core, PA_SUBSCRIPTION_EVENT_SOURCE_OUTPUT | PA_SUBSCRIPTION_EVENT_CHANGE, o->index);
    }

finish:
    pa_xfree(old_value);
}

void pa_source_output_set_property_arbitrary(pa_source_output *o, const char *key, const uint8_t *value, size_t nbytes) {
    const uint8_t *old_value;
    size_t old_nbytes;
    const char *old_value_str;
    const char *new_value_str;

    pa_assert(o);
    pa_assert(key);

    if (pa_proplist_get(o->proplist, key, (const void **) &old_value, &old_nbytes) >= 0) {
        if (value && nbytes == old_nbytes && !memcmp(value, old_value, nbytes))
            return;

        old_value_str = "(data)";

    } else {
        if (!value)
            return;

        old_value_str = "(unset)";
    }

    if (value) {
        pa_proplist_set(o->proplist, key, value, nbytes);
        new_value_str = "(data)";
    } else {
        pa_proplist_unset(o->proplist, key);
        new_value_str = "(unset)";
    }

    if (PA_SOURCE_OUTPUT_IS_LINKED(o->state)) {
        pa_log_debug("Source output %u: proplist[%s]: %s -> %s", o->index, key, old_value_str, new_value_str);
        pa_hook_fire(&o->core->hooks[PA_CORE_HOOK_SOURCE_OUTPUT_PROPLIST_CHANGED], o);
        pa_subscription_post(o->core, PA_SUBSCRIPTION_EVENT_SOURCE_OUTPUT | PA_SUBSCRIPTION_EVENT_CHANGE, o->index);
    }
}

/* Called from main thread */
void pa_source_output_update_proplist(pa_source_output *o, pa_update_mode_t mode, pa_proplist *p) {
    void *state;
    const char *key;
    const uint8_t *value;
    size_t nbytes;

    pa_source_output_assert_ref(o);
    pa_assert(p);
    pa_assert_ctl_context();

    switch (mode) {
        case PA_UPDATE_SET:
            /* Delete everything that is not in p. */
            for (state = NULL; (key = pa_proplist_iterate(o->proplist, &state));) {
                if (!pa_proplist_contains(p, key))
                    pa_source_output_set_property(o, key, NULL);
            }

            /* Fall through. */
        case PA_UPDATE_REPLACE:
            for (state = NULL; (key = pa_proplist_iterate(p, &state));) {
                pa_proplist_get(p, key, (const void **) &value, &nbytes);
                pa_source_output_set_property_arbitrary(o, key, value, nbytes);
            }

            break;
        case PA_UPDATE_MERGE:
            for (state = NULL; (key = pa_proplist_iterate(p, &state));) {
                if (pa_proplist_contains(o->proplist, key))
                    continue;

                pa_proplist_get(p, key, (const void **) &value, &nbytes);
                pa_source_output_set_property_arbitrary(o, key, value, nbytes);
            }

            break;
    }
}

/* Called from main context */
void pa_source_output_cork(pa_source_output *o, bool b) {
    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();
    pa_assert(PA_SOURCE_OUTPUT_IS_LINKED(o->state));

    source_output_set_state(o, b ? PA_SOURCE_OUTPUT_CORKED : PA_SOURCE_OUTPUT_RUNNING);
}

/* Called from main context */
int pa_source_output_set_rate(pa_source_output *o, uint32_t rate) {
    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();
    pa_assert(PA_SOURCE_OUTPUT_IS_LINKED(o->state));
    pa_return_val_if_fail(o->thread_info.resampler, -PA_ERR_BADSTATE);

    if (o->sample_spec.rate == rate)
        return 0;

    o->sample_spec.rate = rate;

    pa_asyncmsgq_post(o->source->asyncmsgq, PA_MSGOBJECT(o), PA_SOURCE_OUTPUT_MESSAGE_SET_RATE, PA_UINT_TO_PTR(rate), 0, NULL, NULL);

    pa_subscription_post(o->core, PA_SUBSCRIPTION_EVENT_SOURCE_OUTPUT|PA_SUBSCRIPTION_EVENT_CHANGE, o->index);
    return 0;
}

/* Called from main context */
pa_resample_method_t pa_source_output_get_resample_method(pa_source_output *o) {
    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();

    return o->actual_resample_method;
}

/* Called from main context */
bool pa_source_output_may_move(pa_source_output *o) {
    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();
    pa_assert(PA_SOURCE_OUTPUT_IS_LINKED(o->state));

    if (o->flags & PA_SOURCE_OUTPUT_DONT_MOVE) {
        pa_log_info("Refused move to new default source!");
        return false;
    }
    if (o->direct_on_input)
        return false;

    return true;
}

static bool find_filter_source_output(pa_source_output *target, pa_source *s) {
    unsigned PA_UNUSED i = 0;
    while (s && s->output_from_master) {
        if (s->output_from_master == target)
            return true;
        s = s->output_from_master->source;
        pa_assert(i++ < 100);
    }
    return false;
}

static bool is_filter_source_moving(pa_source_output *o) {
    pa_source *source = o->source;

    if (!source)
        return false;

    while (source->output_from_master) {
        source = source->output_from_master->source;

        if (!source)
            return true;
    }

    return false;
}

/* Called from main context */
bool pa_source_output_may_move_to(pa_source_output *o, pa_source *dest) {
    pa_source_output_assert_ref(o);
    pa_assert(PA_SOURCE_OUTPUT_IS_LINKED(o->state));
    pa_source_assert_ref(dest);

    if (dest == o->source)
        return true;

    if (dest->unlink_requested)
        return false;

    if (!pa_source_output_may_move(o))
        return false;

    /* Make sure we're not creating a filter source cycle */
    if (find_filter_source_output(o, dest)) {
        pa_log_debug("Can't connect output to %s, as that would create a cycle.", dest->name);
        return false;
    }

    /* If this source output is connected to a filter source that itself is
     * moving, then don't allow the move. Moving requires sending a message to
     * the IO thread of the old source, and if the old source is a filter
     * source that is moving, there's no IO thread associated to the old
     * source. */
    if (is_filter_source_moving(o)) {
        pa_log_debug("Can't move output from filter source %s, because the filter source itself is currently moving.",
                     o->source->name);
        return false;
    }

    if (pa_idxset_size(dest->outputs) >= PA_MAX_OUTPUTS_PER_SOURCE) {
        pa_log_warn("Failed to move source output: too many outputs per source.");
        return false;
    }

    if (o->may_move_to)
        if (!o->may_move_to(o, dest))
            return false;

    return true;
}

/* Called from main context */
int pa_source_output_start_move(pa_source_output *o) {
    pa_source *origin;
    int r;

    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();
    pa_assert(PA_SOURCE_OUTPUT_IS_LINKED(o->state));
    pa_assert(o->source);

    if (!pa_source_output_may_move(o))
        return -PA_ERR_NOTSUPPORTED;

    if ((r = pa_hook_fire(&o->core->hooks[PA_CORE_HOOK_SOURCE_OUTPUT_MOVE_START], o)) < 0)
        return r;

    pa_log_debug("Starting to move source output %u from '%s'", (unsigned) o->index, o->source->name);
    if (o->source) {
        AUDIO_INFO_LOG("[StartMove]: SourceOutput[%{public}u] --xxxx--> source[%{public}u, %{public}s]",
            o->index, o->source->index, o->source->name);
    }

    origin = o->source;

    pa_idxset_remove_by_data(o->source->outputs, o, NULL);

    if (o->state == PA_SOURCE_OUTPUT_CORKED)
        pa_assert_se(origin->n_corked-- >= 1);

    if (pa_source_output_is_passthrough(o))
        pa_source_leave_passthrough(o->source);

    if (pa_source_flat_volume_enabled(o->source))
        /* We might need to update the source's volume if we are in flat
         * volume mode. */
        pa_source_set_volume(o->source, NULL, false, false);

    pa_assert_se(pa_asyncmsgq_send(o->source->asyncmsgq, PA_MSGOBJECT(o->source), PA_SOURCE_MESSAGE_REMOVE_OUTPUT, o, 0, NULL) == 0);

    pa_source_update_status(o->source);

    pa_cvolume_remap(&o->volume_factor_source, &o->source->channel_map, &o->channel_map);

    o->source = NULL;
    o->source_requested_by_application = false;

    pa_source_output_unref(o);

    return 0;
}

/* Called from main context. If it has an origin source that uses volume sharing,
 * then also the origin source and all streams connected to it need to update
 * their volume - this function does all that by using recursion. */
static void update_volume_due_to_moving(pa_source_output *o, pa_source *dest) {
    pa_cvolume new_volume;

    pa_assert(o);
    pa_assert(dest);
    pa_assert(o->source); /* The destination source should already be set. */

    if (o->destination_source && (o->destination_source->flags & PA_SOURCE_SHARE_VOLUME_WITH_MASTER)) {
        pa_source *root_source;
        pa_source_output *destination_source_output;
        uint32_t idx;

        root_source = pa_source_get_master(o->source);

        if (PA_UNLIKELY(!root_source))
            return;

        if (pa_source_flat_volume_enabled(o->source)) {
            /* Ok, so the origin source uses volume sharing, and flat volume is
             * enabled. The volume will have to be updated as follows:
             *
             *     o->volume := o->source->real_volume
             *         (handled later by pa_source_set_volume)
             *     o->reference_ratio := o->volume / o->source->reference_volume
             *         (handled later by pa_source_set_volume)
             *     o->real_ratio stays unchanged
             *         (streams whose origin source uses volume sharing should
             *          always have real_ratio of 0 dB)
             *     o->soft_volume stays unchanged
             *         (streams whose origin source uses volume sharing should
             *          always have volume_factor as soft_volume, so no change
             *          should be needed) */

            pa_assert(pa_cvolume_is_norm(&o->real_ratio));
            pa_assert(pa_cvolume_equal(&o->soft_volume, &o->volume_factor));

            /* Notifications will be sent by pa_source_set_volume(). */

        } else {
            /* Ok, so the origin source uses volume sharing, and flat volume is
             * disabled. The volume will have to be updated as follows:
             *
             *     o->volume := 0 dB
             *     o->reference_ratio := 0 dB
             *     o->real_ratio stays unchanged
             *         (streams whose origin source uses volume sharing should
             *          always have real_ratio of 0 dB)
             *     o->soft_volume stays unchanged
             *         (streams whose origin source uses volume sharing should
             *          always have volume_factor as soft_volume, so no change
             *          should be needed) */

            pa_cvolume_reset(&new_volume, o->volume.channels);
            pa_source_output_set_volume_direct(o, &new_volume);
            pa_source_output_set_reference_ratio(o, &new_volume);
            pa_assert(pa_cvolume_is_norm(&o->real_ratio));
            pa_assert(pa_cvolume_equal(&o->soft_volume, &o->volume_factor));
        }

        /* Additionally, the origin source volume needs updating:
         *
         *     o->destination_source->reference_volume := root_source->reference_volume
         *     o->destination_source->real_volume := root_source->real_volume
         *     o->destination_source->soft_volume stays unchanged
         *         (sources that use volume sharing should always have
         *          soft_volume of 0 dB) */

        new_volume = root_source->reference_volume;
        pa_cvolume_remap(&new_volume, &root_source->channel_map, &o->destination_source->channel_map);
        pa_source_set_reference_volume_direct(o->destination_source, &new_volume);

        o->destination_source->real_volume = root_source->real_volume;
        pa_cvolume_remap(&o->destination_source->real_volume, &root_source->channel_map, &o->destination_source->channel_map);

        pa_assert(pa_cvolume_is_norm(&o->destination_source->soft_volume));

        /* If you wonder whether o->destination_source->set_volume() should be
         * called somewhere, that's not the case, because sources that use
         * volume sharing shouldn't have any internal volume that set_volume()
         * would update. If you wonder whether the thread_info variables should
         * be synced, yes, they should, and it's done by the
         * PA_SOURCE_MESSAGE_FINISH_MOVE message handler. */

        /* Recursively update origin source outputs. */
        PA_IDXSET_FOREACH(destination_source_output, o->destination_source->outputs, idx)
            update_volume_due_to_moving(destination_source_output, dest);

    } else {
        if (pa_source_flat_volume_enabled(o->source)) {
            /* Ok, so this is a regular stream, and flat volume is enabled. The
             * volume will have to be updated as follows:
             *
             *     o->volume := o->reference_ratio * o->source->reference_volume
             *     o->reference_ratio stays unchanged
             *     o->real_ratio := o->volume / o->source->real_volume
             *         (handled later by pa_source_set_volume)
             *     o->soft_volume := o->real_ratio * o->volume_factor
             *         (handled later by pa_source_set_volume) */

            new_volume = o->source->reference_volume;
            pa_cvolume_remap(&new_volume, &o->source->channel_map, &o->channel_map);
            pa_sw_cvolume_multiply(&new_volume, &new_volume, &o->reference_ratio);
            pa_source_output_set_volume_direct(o, &new_volume);

        } else {
            /* Ok, so this is a regular stream, and flat volume is disabled.
             * The volume will have to be updated as follows:
             *
             *     o->volume := o->reference_ratio
             *     o->reference_ratio stays unchanged
             *     o->real_ratio := o->reference_ratio
             *     o->soft_volume := o->real_ratio * o->volume_factor */

            pa_source_output_set_volume_direct(o, &o->reference_ratio);
            o->real_ratio = o->reference_ratio;
            pa_sw_cvolume_multiply(&o->soft_volume, &o->real_ratio, &o->volume_factor);

            /* If this is a virtual source stream, we have to apply the source volume
             * to the source output. */
            if (o->destination_source) {
                pa_cvolume vol;

                vol = o->destination_source->real_volume;
                pa_cvolume_remap(&vol, &o->destination_source->channel_map, &o->channel_map);
                pa_source_output_set_volume(o, &vol, o->destination_source->save_volume, true);
            }
        }
    }

    /* If o->source == dest, then recursion has finished, and we can finally call
     * pa_source_set_volume(), which will do the rest of the updates. */
    if ((o->source == dest) && pa_source_flat_volume_enabled(o->source))
        pa_source_set_volume(o->source, NULL, false, o->save_volume);
}

/* Called from the main thread. */
static void set_preferred_source(pa_source_output *o, const char *source_name) {
    pa_assert(o);

    if (pa_safe_streq(o->preferred_source, source_name))
        return;

    pa_log_debug("Source output %u: preferred_source: %s -> %s",
                 o->index, o->preferred_source ? o->preferred_source : "(unset)", source_name ? source_name : "(unset)");
    pa_xfree(o->preferred_source);
    o->preferred_source = pa_xstrdup(source_name);

    pa_subscription_post(o->core, PA_SUBSCRIPTION_EVENT_SOURCE_OUTPUT | PA_SUBSCRIPTION_EVENT_CHANGE, o->index);
    pa_hook_fire(&o->core->hooks[PA_CORE_HOOK_SOURCE_OUTPUT_PREFERRED_SOURCE_CHANGED], o);
}

/* Called from main context */
int pa_source_output_finish_move(pa_source_output *o, pa_source *dest, bool save) {
    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();
    pa_assert(PA_SOURCE_OUTPUT_IS_LINKED(o->state));
    pa_assert(!o->source);
    pa_source_assert_ref(dest);

    if (!pa_source_output_may_move_to(o, dest))
        return -PA_ERR_NOTSUPPORTED;

    if (pa_source_output_is_passthrough(o) && !pa_source_check_format(dest, o->format)) {
        pa_proplist *p = pa_proplist_new();
        pa_log_debug("New source doesn't support stream format, sending format-changed and killing");
        /* Tell the client what device we want to be on if it is going to
         * reconnect */
        pa_proplist_sets(p, "device", dest->name);
        pa_source_output_send_event(o, PA_STREAM_EVENT_FORMAT_LOST, p);
        pa_proplist_free(p);
        return -PA_ERR_NOTSUPPORTED;
    }

    if (!(o->flags & PA_SOURCE_OUTPUT_VARIABLE_RATE) &&
        !pa_sample_spec_equal(&o->sample_spec, &dest->sample_spec)) {
        /* try to change dest source format and rate if possible without glitches.
           module-suspend-on-idle resumes destination source with
           SOURCE_OUTPUT_MOVE_FINISH hook */

        pa_log_info("Trying to change sample spec");
        pa_source_reconfigure(dest, &o->sample_spec, pa_source_output_is_passthrough(o));
    }

    if (o->moving)
        o->moving(o, dest);

    o->source = dest;
    if (dest) {
        AUDIO_INFO_LOG("[FinishMove]: SourceOutput[%{public}u] ----------> source[%{public}u, %{public}s]",
            o->index, dest->index, dest->name);
    }

    /* save == true, means user is calling the move_to() and want to
       save the preferred_source */
    if (save) {
        if (dest == dest->core->default_source)
            set_preferred_source(o, NULL);
        else
            set_preferred_source(o, dest->name);
    }

    pa_idxset_put(o->source->outputs, pa_source_output_ref(o), NULL);

    pa_cvolume_remap(&o->volume_factor_source, &o->channel_map, &o->source->channel_map);

    if (o->state == PA_SOURCE_OUTPUT_CORKED)
        o->source->n_corked++;

    pa_source_output_update_resampler(o);

    pa_source_update_status(dest);

    update_volume_due_to_moving(o, dest);

    if (pa_source_output_is_passthrough(o))
        pa_source_enter_passthrough(o->source);

    pa_assert_se(pa_asyncmsgq_send(o->source->asyncmsgq, PA_MSGOBJECT(o->source), PA_SOURCE_MESSAGE_ADD_OUTPUT, o, 0, NULL) == 0);

    pa_log_debug("Successfully moved source output %i to %s.", o->index, dest->name);

    /* Notify everyone */
    pa_hook_fire(&o->core->hooks[PA_CORE_HOOK_SOURCE_OUTPUT_MOVE_FINISH], o);
    pa_subscription_post(o->core, PA_SUBSCRIPTION_EVENT_SOURCE_OUTPUT|PA_SUBSCRIPTION_EVENT_CHANGE, o->index);

    return 0;
}

/* Called from main context */
void pa_source_output_fail_move(pa_source_output *o) {

    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();
    pa_assert(PA_SOURCE_OUTPUT_IS_LINKED(o->state));
    pa_assert(!o->source);

    /* Check if someone wants this source output? */
    if (pa_hook_fire(&o->core->hooks[PA_CORE_HOOK_SOURCE_OUTPUT_MOVE_FAIL], o) == PA_HOOK_STOP)
        return;

    /* Can we move the source output to the default source? */
    if (o->core->rescue_streams && pa_source_output_may_move_to(o, o->core->default_source)) {
        if (pa_source_output_finish_move(o, o->core->default_source, false) >= 0)
            return;
    }

    AUDIO_WARNING_LOG("[FailMove]: SourceOutput[%{public}u] moving FAILED.", o->index);
    if (o->moving)
        o->moving(o, NULL);

    pa_source_output_kill(o);
}

/* Called from main context */
int pa_source_output_move_to(pa_source_output *o, pa_source *dest, bool save) {
    int r;

    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();
    pa_assert(PA_SOURCE_OUTPUT_IS_LINKED(o->state));
    pa_assert(o->source);
    pa_source_assert_ref(dest);

    if (dest == o->source)
        return 0;

    if (!pa_source_output_may_move_to(o, dest))
        return -PA_ERR_NOTSUPPORTED;

    pa_source_output_ref(o);

    if ((r = pa_source_output_start_move(o)) < 0) {
        pa_source_output_unref(o);
        return r;
    }

    if ((r = pa_source_output_finish_move(o, dest, save)) < 0) {
        pa_source_output_fail_move(o);
        pa_source_output_unref(o);
        return r;
    }

    pa_source_output_unref(o);

    return 0;
}

/* Called from IO thread context except when cork() is called without a valid source. */
void pa_source_output_set_state_within_thread(pa_source_output *o, pa_source_output_state_t state) {
    pa_source_output_assert_ref(o);

    if (state == o->thread_info.state)
        return;

    if (o->state_change)
        o->state_change(o, state);

    o->thread_info.state = state;
}

/* Called from IO thread context, except when it is not */
int pa_source_output_process_msg(pa_msgobject *mo, int code, void *userdata, int64_t offset, pa_memchunk* chunk) {
    pa_source_output *o = PA_SOURCE_OUTPUT(mo);
    pa_source_output_assert_ref(o);

    switch (code) {

        case PA_SOURCE_OUTPUT_MESSAGE_GET_LATENCY: {
            pa_usec_t *r = userdata;

            r[0] += pa_bytes_to_usec(pa_memblockq_get_length(o->thread_info.delay_memblockq), &o->source->sample_spec);
            r[0] += pa_resampler_get_delay_usec(o->thread_info.resampler);
            r[1] += pa_source_get_latency_within_thread(o->source, false);

            return 0;
        }

        case PA_SOURCE_OUTPUT_MESSAGE_SET_RATE:

            o->thread_info.sample_spec.rate = PA_PTR_TO_UINT(userdata);
            pa_resampler_set_output_rate(o->thread_info.resampler, PA_PTR_TO_UINT(userdata));
            return 0;

        case PA_SOURCE_OUTPUT_MESSAGE_SET_STATE:

            pa_source_output_set_state_within_thread(o, PA_PTR_TO_UINT(userdata));

            return 0;

        case PA_SOURCE_OUTPUT_MESSAGE_SET_REQUESTED_LATENCY: {
            pa_usec_t *usec = userdata;

            *usec = pa_source_output_set_requested_latency_within_thread(o, *usec);

            return 0;
        }

        case PA_SOURCE_OUTPUT_MESSAGE_GET_REQUESTED_LATENCY: {
            pa_usec_t *r = userdata;

            *r = o->thread_info.requested_source_latency;
            return 0;
        }

        case PA_SOURCE_OUTPUT_MESSAGE_SET_SOFT_VOLUME:
            if (!pa_cvolume_equal(&o->thread_info.soft_volume, &o->soft_volume)) {
                o->thread_info.soft_volume = o->soft_volume;
            }
            return 0;

        case PA_SOURCE_OUTPUT_MESSAGE_SET_SOFT_MUTE:
            if (o->thread_info.muted != o->muted) {
                o->thread_info.muted = o->muted;
            }
            return 0;
    }

    return -PA_ERR_NOTIMPLEMENTED;
}

/* Called from main context */
void pa_source_output_send_event(pa_source_output *o, const char *event, pa_proplist *data) {
    pa_proplist *pl = NULL;
    pa_source_output_send_event_hook_data hook_data;

    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();
    pa_assert(event);

    if (!o->send_event)
        return;

    if (!data)
        data = pl = pa_proplist_new();

    hook_data.source_output = o;
    hook_data.data = data;
    hook_data.event = event;

    if (pa_hook_fire(&o->core->hooks[PA_CORE_HOOK_SOURCE_OUTPUT_SEND_EVENT], &hook_data) < 0)
        goto finish;

    o->send_event(o, event, data);

finish:
    if (pl)
        pa_proplist_free(pl);
}

/* Called from main context */
/* Updates the source output's resampler with whatever the current source
 * requires -- useful when the underlying source's sample spec might have changed */
int pa_source_output_update_resampler(pa_source_output *o) {
    pa_resampler *new_resampler;
    char *memblockq_name;
    size_t resampler_history;

    pa_source_output_assert_ref(o);
    pa_assert_ctl_context();

    if (o->thread_info.resampler &&
        pa_sample_spec_equal(pa_resampler_input_sample_spec(o->thread_info.resampler), &o->source->sample_spec) &&
        pa_channel_map_equal(pa_resampler_input_channel_map(o->thread_info.resampler), &o->source->channel_map))

        new_resampler = o->thread_info.resampler;

    else if (!pa_source_output_is_passthrough(o) &&
        ((o->flags & PA_SOURCE_OUTPUT_VARIABLE_RATE) ||
         !pa_sample_spec_equal(&o->sample_spec, &o->source->sample_spec) ||
         !pa_channel_map_equal(&o->channel_map, &o->source->channel_map))) {

        new_resampler = pa_resampler_new(o->core->mempool,
                                     &o->source->sample_spec, &o->source->channel_map,
                                     &o->sample_spec, &o->channel_map,
                                     o->core->lfe_crossover_freq,
                                     o->requested_resample_method,
                                     ((o->flags & PA_SOURCE_OUTPUT_VARIABLE_RATE) ? PA_RESAMPLER_VARIABLE_RATE : 0) |
                                     ((o->flags & PA_SOURCE_OUTPUT_NO_REMAP) ? PA_RESAMPLER_NO_REMAP : 0) |
                                     (o->core->disable_remixing || (o->flags & PA_SOURCE_OUTPUT_NO_REMIX) ? PA_RESAMPLER_NO_REMIX : 0) |
                                     (o->core->remixing_use_all_sink_channels ? 0 : PA_RESAMPLER_NO_FILL_SINK) |
                                     (o->core->remixing_produce_lfe ? PA_RESAMPLER_PRODUCE_LFE : 0) |
                                     (o->core->remixing_consume_lfe ? PA_RESAMPLER_CONSUME_LFE : 0));

        if (!new_resampler) {
            pa_log_warn("Unsupported resampling operation.");
            return -PA_ERR_NOTSUPPORTED;
        }
    } else
        new_resampler = NULL;

    if (new_resampler == o->thread_info.resampler)
        return 0;

    if (o->thread_info.resampler)
        pa_resampler_free(o->thread_info.resampler);

    o->thread_info.resampler = new_resampler;

    pa_memblockq_free(o->thread_info.delay_memblockq);

    memblockq_name = pa_sprintf_malloc("source output delay_memblockq [%u]", o->index);
    o->thread_info.delay_memblockq = pa_memblockq_new(
            memblockq_name,
            0,
            MEMBLOCKQ_MAXLENGTH,
            0,
            &o->source->sample_spec,
            0,
            1,
            0,
            &o->source->silence);
    pa_xfree(memblockq_name);

    resampler_history = (uint64_t) PA_RESAMPLER_MAX_DELAY_USEC * o->source->sample_spec.rate / PA_USEC_PER_SEC;
    resampler_history *= pa_frame_size(&o->source->sample_spec);

    pa_memblockq_set_maxrewind(o->thread_info.delay_memblockq, resampler_history + pa_source_get_max_rewind(o->source));

    o->actual_resample_method = new_resampler ? pa_resampler_get_method(new_resampler) : PA_RESAMPLER_INVALID;

    pa_log_debug("Updated resampler for source output %d", o->index);

    return 0;
}

/* Called from the IO thread. */
void pa_source_output_attach(pa_source_output *o) {
    pa_assert(o);
    pa_assert(!o->thread_info.attached);

    o->thread_info.attached = true;

    if (o->attach)
        o->attach(o);
}

/* Called from the IO thread. */
void pa_source_output_detach(pa_source_output *o) {
    pa_assert(o);

    if (!o->thread_info.attached)
        return;

    o->thread_info.attached = false;

    if (o->detach)
        o->detach(o);
}

/* Called from the main thread. */
void pa_source_output_set_volume_direct(pa_source_output *o, const pa_cvolume *volume) {
    pa_cvolume old_volume;
    char old_volume_str[PA_CVOLUME_SNPRINT_VERBOSE_MAX];
    char new_volume_str[PA_CVOLUME_SNPRINT_VERBOSE_MAX];

    pa_assert(o);
    pa_assert(volume);

    old_volume = o->volume;

    if (pa_cvolume_equal(volume, &old_volume))
        return;

    o->volume = *volume;
    pa_log_debug("The volume of source output %u changed from %s to %s.", o->index,
                 pa_cvolume_snprint_verbose(old_volume_str, sizeof(old_volume_str), &old_volume, &o->channel_map, true),
                 pa_cvolume_snprint_verbose(new_volume_str, sizeof(new_volume_str), volume, &o->channel_map, true));

    if (o->volume_changed)
        o->volume_changed(o);

    pa_subscription_post(o->core, PA_SUBSCRIPTION_EVENT_SOURCE_OUTPUT|PA_SUBSCRIPTION_EVENT_CHANGE, o->index);
    pa_hook_fire(&o->core->hooks[PA_CORE_HOOK_SOURCE_OUTPUT_VOLUME_CHANGED], o);
}

/* Called from the main thread. */
void pa_source_output_set_reference_ratio(pa_source_output *o, const pa_cvolume *ratio) {
    pa_cvolume old_ratio;
    char old_ratio_str[PA_CVOLUME_SNPRINT_VERBOSE_MAX];
    char new_ratio_str[PA_CVOLUME_SNPRINT_VERBOSE_MAX];

    pa_assert(o);
    pa_assert(ratio);

    old_ratio = o->reference_ratio;

    if (pa_cvolume_equal(ratio, &old_ratio))
        return;

    o->reference_ratio = *ratio;

    if (!PA_SOURCE_OUTPUT_IS_LINKED(o->state))
        return;

    pa_log_debug("Source output %u reference ratio changed from %s to %s.", o->index,
                 pa_cvolume_snprint_verbose(old_ratio_str, sizeof(old_ratio_str), &old_ratio, &o->channel_map, true),
                 pa_cvolume_snprint_verbose(new_ratio_str, sizeof(new_ratio_str), ratio, &o->channel_map, true));
}

/* Called from the main thread.
 *
 * This is called when e.g. module-stream-restore wants to change the preferred
 * source. As a side effect the stream is moved to the new preferred source.
 * Note that things can work also in the other direction: if the user moves
 * a stream, as a side effect the preferred source is changed. This could cause
 * an infinite loop, but it's avoided by these two measures:
 *   - When pa_source_output_set_preferred_source() is called, it calls
 *     pa_source_output_move_to() with save=false, which avoids the recursive
 *     pa_source_output_set_preferred_source() call.
 *   - When the primary operation is to move a stream,
 *     pa_source_output_finish_move() calls set_preferred_source() instead of
 *     pa_source_output_set_preferred_source(). set_preferred_source() doesn't
 *     move the stream as a side effect.
 */
void pa_source_output_set_preferred_source(pa_source_output *o, pa_source *s) {
    pa_assert(o);

    if (s) {
        set_preferred_source(o, s->name);
        pa_source_output_move_to(o, s, false);
    } else {
        set_preferred_source(o, NULL);
        pa_source_output_move_to(o, o->core->default_source, false);
    }
}