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rtpdec_h263.c
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1 /*
2  * RTP H.263 Depacketizer, RFC 4629
3  * Copyright (c) 2010 Martin Storsjo
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 "rtpdec_formats.h"
24 #include "libavutil/attributes.h"
25 #include "libavutil/intreadwrite.h"
26 
27 static av_cold int h263_init(AVFormatContext *ctx, int st_index,
29 {
30  if (st_index < 0)
31  return 0;
32  ctx->streams[st_index]->need_parsing = AVSTREAM_PARSE_FULL;
33  return 0;
34 }
35 
37  AVStream *st, AVPacket *pkt, uint32_t *timestamp,
38  const uint8_t *buf, int len, uint16_t seq, int flags)
39 {
40  uint8_t *ptr;
41  uint16_t header;
42  int startcode, vrc, picture_header;
43 
44  if (len < 2) {
45  av_log(ctx, AV_LOG_ERROR, "Too short H.263 RTP packet\n");
46  return AVERROR_INVALIDDATA;
47  }
48 
49  /* Decode the 16 bit H.263+ payload header, as described in section
50  * 5.1 of RFC 4629. The fields of this header are:
51  * - 5 reserved bits, should be ignored.
52  * - One bit (P, startcode), indicating a picture start, picture segment
53  * start or video sequence end. If set, two zero bytes should be
54  * prepended to the payload.
55  * - One bit (V, vrc), indicating the presence of an 8 bit Video
56  * Redundancy Coding field after this 16 bit header.
57  * - 6 bits (PLEN, picture_header), the length (in bytes) of an extra
58  * picture header, following the VRC field.
59  * - 3 bits (PEBIT), the number of bits to ignore of the last byte
60  * of the extra picture header. (Not used at the moment.)
61  */
62  header = AV_RB16(buf);
63  startcode = (header & 0x0400) >> 9;
64  vrc = header & 0x0200;
65  picture_header = (header & 0x01f8) >> 3;
66  buf += 2;
67  len -= 2;
68 
69  if (vrc) {
70  /* Skip VRC header if present, not used at the moment. */
71  buf += 1;
72  len -= 1;
73  }
74  if (picture_header) {
75  /* Skip extra picture header if present, not used at the moment. */
76  buf += picture_header;
77  len -= picture_header;
78  }
79 
80  if (len < 0) {
81  av_log(ctx, AV_LOG_ERROR, "Too short H.263 RTP packet\n");
82  return AVERROR_INVALIDDATA;
83  }
84 
85  if (av_new_packet(pkt, len + startcode)) {
86  av_log(ctx, AV_LOG_ERROR, "Out of memory\n");
87  return AVERROR(ENOMEM);
88  }
89  pkt->stream_index = st->index;
90  ptr = pkt->data;
91 
92  if (startcode) {
93  *ptr++ = 0;
94  *ptr++ = 0;
95  }
96  memcpy(ptr, buf, len);
97 
98  return 0;
99 }
100 
102  .enc_name = "H263-1998",
103  .codec_type = AVMEDIA_TYPE_VIDEO,
104  .codec_id = AV_CODEC_ID_H263,
105  .init = h263_init,
106  .parse_packet = ff_h263_handle_packet,
107 };
108 
110  .enc_name = "H263-2000",
111  .codec_type = AVMEDIA_TYPE_VIDEO,
112  .codec_id = AV_CODEC_ID_H263,
113  .init = h263_init,
114  .parse_packet = ff_h263_handle_packet,
115 };