1 /*
2 * RTP packetization for H.261 video (RFC 4587)
3 * Copyright (c) 2014 Thomas Volkert <thomas@homer-conferencing.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 "avformat.h"
23 #include "rtpenc.h"
24
25 #define RTP_H261_HEADER_SIZE 4
26
find_resync_marker_reverse(const uint8_t * av_restrict start,const uint8_t * av_restrict end)27 static const uint8_t *find_resync_marker_reverse(const uint8_t *av_restrict start,
28 const uint8_t *av_restrict end)
29 {
30 const uint8_t *p = end - 1;
31 start += 1; /* Make sure we never return the original start. */
32 for (; p > start; p--) {
33 if (p[0] == 0 && p[1] == 1)
34 return p;
35 }
36 return end;
37 }
38
ff_rtp_send_h261(AVFormatContext * ctx,const uint8_t * frame_buf,int frame_size)39 void ff_rtp_send_h261(AVFormatContext *ctx, const uint8_t *frame_buf, int frame_size)
40 {
41 int cur_frame_size;
42 int last_packet_of_frame;
43 RTPMuxContext *rtp_ctx = ctx->priv_data;
44
45 /* use the default 90 KHz time stamp */
46 rtp_ctx->timestamp = rtp_ctx->cur_timestamp;
47
48 /* continue as long as not all frame data is processed */
49 while (frame_size > 0) {
50 /*
51 * encode the H.261 payload header according to section 4.1 of RFC 4587:
52 * (uses 4 bytes between RTP header and H.261 stream per packet)
53 *
54 * 0 1 2 3
55 * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
56 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
57 * |SBIT |EBIT |I|V| GOBN | MBAP | QUANT | HMVD | VMVD |
58 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
59 *
60 * Start bit position (SBIT): 3 bits
61 * End bit position (EBIT): 3 bits
62 * INTRA-frame encoded data (I): 1 bit
63 * Motion Vector flag (V): 1 bit
64 * GOB number (GOBN): 4 bits
65 * Macroblock address predictor (MBAP): 5 bits
66 * Quantizer (QUANT): 5 bits
67 * Horizontal motion vector data (HMVD): 5 bits
68 * Vertical motion vector data (VMVD): 5 bits
69 */
70 rtp_ctx->buf[0] = 1; /* sbit=0, ebit=0, i=0, v=1 */
71 rtp_ctx->buf[1] = 0; /* gobn=0, mbap=0 */
72 rtp_ctx->buf[2] = 0; /* quant=0, hmvd=5 */
73 rtp_ctx->buf[3] = 0; /* vmvd=0 */
74 if (frame_size < 2 || frame_buf[0] != 0 || frame_buf[1] != 1) {
75 /* A full, correct fix for this would be to make the H.261 encoder
76 * support inserting extra GOB headers (triggered by setting e.g.
77 * "-ps 1"), and including information about macroblock boundaries
78 * (such as for h263_rfc2190). */
79 av_log(ctx, AV_LOG_WARNING,
80 "RTP/H.261 packet not cut at a GOB boundary, not signaled correctly\n");
81 }
82
83 cur_frame_size = FFMIN(rtp_ctx->max_payload_size - RTP_H261_HEADER_SIZE, frame_size);
84
85 /* look for a better place to split the frame into packets */
86 if (cur_frame_size < frame_size) {
87 const uint8_t *packet_end = find_resync_marker_reverse(frame_buf,
88 frame_buf + cur_frame_size);
89 cur_frame_size = packet_end - frame_buf;
90 }
91
92 /* calculate the "marker" bit for the RTP header */
93 last_packet_of_frame = cur_frame_size == frame_size;
94
95 /* complete and send RTP packet */
96 memcpy(&rtp_ctx->buf[RTP_H261_HEADER_SIZE], frame_buf, cur_frame_size);
97 ff_rtp_send_data(ctx, rtp_ctx->buf, RTP_H261_HEADER_SIZE + cur_frame_size, last_packet_of_frame);
98
99 frame_buf += cur_frame_size;
100 frame_size -= cur_frame_size;
101 }
102 }
103