1 /*
2 * Bitstream filter for unpacking DivX-style packed B-frames in MPEG-4 (divx_packed)
3 * Copyright (c) 2015 Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
4 *
5 * This file is part of FFmpeg.
6 *
7 * FFmpeg is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
11 *
12 * FFmpeg is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with FFmpeg; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20 */
21
22 #include "bsf.h"
23 #include "bsf_internal.h"
24 #include "internal.h"
25 #include "mpeg4video.h"
26
27 typedef struct UnpackBFramesBSFContext {
28 AVBufferRef *b_frame_ref;
29 } UnpackBFramesBSFContext;
30
31 /* determine the position of the packed marker in the userdata,
32 * the number of VOPs and the position of the second VOP */
scan_buffer(const uint8_t * buf,int buf_size,int * pos_p,int * nb_vop,int * pos_vop2)33 static void scan_buffer(const uint8_t *buf, int buf_size,
34 int *pos_p, int *nb_vop, int *pos_vop2) {
35 uint32_t startcode;
36 const uint8_t *end = buf + buf_size, *pos = buf;
37
38 while (pos < end) {
39 startcode = -1;
40 pos = avpriv_find_start_code(pos, end, &startcode);
41
42 if (startcode == USER_DATA_STARTCODE && pos_p) {
43 /* check if the (DivX) userdata string ends with 'p' (packed) */
44 for (int i = 0; i < 255 && pos + i + 1 < end; i++) {
45 if (pos[i] == 'p' && pos[i + 1] == '\0') {
46 *pos_p = pos + i - buf;
47 break;
48 }
49 }
50 } else if (startcode == VOP_STARTCODE && nb_vop) {
51 *nb_vop += 1;
52 if (*nb_vop == 2 && pos_vop2) {
53 *pos_vop2 = pos - buf - 4; /* subtract 4 bytes startcode */
54 }
55 }
56 }
57 }
58
mpeg4_unpack_bframes_filter(AVBSFContext * ctx,AVPacket * pkt)59 static int mpeg4_unpack_bframes_filter(AVBSFContext *ctx, AVPacket *pkt)
60 {
61 UnpackBFramesBSFContext *s = ctx->priv_data;
62 int pos_p = -1, nb_vop = 0, pos_vop2 = -1, ret = 0;
63
64 ret = ff_bsf_get_packet_ref(ctx, pkt);
65 if (ret < 0)
66 return ret;
67
68 scan_buffer(pkt->data, pkt->size, &pos_p, &nb_vop, &pos_vop2);
69 av_log(ctx, AV_LOG_DEBUG, "Found %d VOP startcode(s) in this packet.\n", nb_vop);
70
71 if (pos_vop2 >= 0) {
72 if (s->b_frame_ref) {
73 av_log(ctx, AV_LOG_WARNING,
74 "Missing one N-VOP packet, discarding one B-frame.\n");
75 av_buffer_unref(&s->b_frame_ref);
76 }
77 /* store a reference to the packed B-frame's data in the BSFContext */
78 s->b_frame_ref = av_buffer_ref(pkt->buf);
79 if (!s->b_frame_ref) {
80 ret = AVERROR(ENOMEM);
81 goto fail;
82 }
83 s->b_frame_ref->data = pkt->data + pos_vop2;
84 s->b_frame_ref->size = pkt->size - pos_vop2;
85 }
86
87 if (nb_vop > 2) {
88 av_log(ctx, AV_LOG_WARNING,
89 "Found %d VOP headers in one packet, only unpacking one.\n", nb_vop);
90 }
91
92 if (nb_vop == 1 && s->b_frame_ref) {
93 AVBufferRef *tmp = pkt->buf;
94
95 /* make tmp accurately reflect the packet's data */
96 tmp->data = pkt->data;
97 tmp->size = pkt->size;
98
99 /* replace data in packet with stored data */
100 pkt->buf = s->b_frame_ref;
101 pkt->data = s->b_frame_ref->data;
102 pkt->size = s->b_frame_ref->size;
103
104 /* store reference to data into BSFContext */
105 s->b_frame_ref = tmp;
106
107 if (s->b_frame_ref->size <= MAX_NVOP_SIZE) {
108 /* N-VOP - discard stored data */
109 av_log(ctx, AV_LOG_DEBUG, "Skipping N-VOP.\n");
110 av_buffer_unref(&s->b_frame_ref);
111 }
112 } else if (nb_vop >= 2) {
113 /* use first frame of the packet */
114 pkt->size = pos_vop2;
115 } else if (pos_p >= 0) {
116 ret = av_packet_make_writable(pkt);
117 if (ret < 0)
118 goto fail;
119 av_log(ctx, AV_LOG_DEBUG, "Updating DivX userdata (remove trailing 'p').\n");
120 /* remove 'p' (packed) from the end of the (DivX) userdata string */
121 pkt->data[pos_p] = '\0';
122 } else {
123 /* use packet as is */
124 }
125
126 fail:
127 if (ret < 0)
128 av_packet_unref(pkt);
129
130 return ret;
131 }
132
mpeg4_unpack_bframes_init(AVBSFContext * ctx)133 static int mpeg4_unpack_bframes_init(AVBSFContext *ctx)
134 {
135 if (ctx->par_in->extradata) {
136 int pos_p_ext = -1;
137 scan_buffer(ctx->par_in->extradata, ctx->par_in->extradata_size, &pos_p_ext, NULL, NULL);
138 if (pos_p_ext >= 0) {
139 av_log(ctx, AV_LOG_DEBUG,
140 "Updating DivX userdata (remove trailing 'p') in extradata.\n");
141 ctx->par_out->extradata[pos_p_ext] = '\0';
142 }
143 }
144
145 return 0;
146 }
147
mpeg4_unpack_bframes_close_flush(AVBSFContext * bsfc)148 static void mpeg4_unpack_bframes_close_flush(AVBSFContext *bsfc)
149 {
150 UnpackBFramesBSFContext *ctx = bsfc->priv_data;
151 av_buffer_unref(&ctx->b_frame_ref);
152 }
153
154 static const enum AVCodecID codec_ids[] = {
155 AV_CODEC_ID_MPEG4, AV_CODEC_ID_NONE,
156 };
157
158 const AVBitStreamFilter ff_mpeg4_unpack_bframes_bsf = {
159 .name = "mpeg4_unpack_bframes",
160 .priv_data_size = sizeof(UnpackBFramesBSFContext),
161 .init = mpeg4_unpack_bframes_init,
162 .filter = mpeg4_unpack_bframes_filter,
163 .flush = mpeg4_unpack_bframes_close_flush,
164 .close = mpeg4_unpack_bframes_close_flush,
165 .codec_ids = codec_ids,
166 };
167