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 Libav.
6  *
7  * Libav 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  * Libav 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 Libav; 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/intreadwrite.h"
25 
28  AVStream *st,
29  AVPacket * pkt,
30  uint32_t * timestamp,
31  const uint8_t * buf,
32  int len, int flags)
33 {
34  uint8_t *ptr;
35  uint16_t header;
36  int startcode, vrc, picture_header;
37 
38  if (len < 2) {
39  av_log(ctx, AV_LOG_ERROR, "Too short H.263 RTP packet\n");
40  return AVERROR_INVALIDDATA;
41  }
42 
43  /* Decode the 16 bit H.263+ payload header, as described in section
44  * 5.1 of RFC 4629. The fields of this header are:
45  * - 5 reserved bits, should be ignored.
46  * - One bit (P, startcode), indicating a picture start, picture segment
47  * start or video sequence end. If set, two zero bytes should be
48  * prepended to the payload.
49  * - One bit (V, vrc), indicating the presence of an 8 bit Video
50  * Redundancy Coding field after this 16 bit header.
51  * - 6 bits (PLEN, picture_header), the length (in bytes) of an extra
52  * picture header, following the VRC field.
53  * - 3 bits (PEBIT), the number of bits to ignore of the last byte
54  * of the extra picture header. (Not used at the moment.)
55  */
56  header = AV_RB16(buf);
57  startcode = (header & 0x0400) >> 9;
58  vrc = header & 0x0200;
59  picture_header = (header & 0x01f8) >> 3;
60  buf += 2;
61  len -= 2;
62 
63  if (vrc) {
64  /* Skip VRC header if present, not used at the moment. */
65  buf += 1;
66  len -= 1;
67  }
68  if (picture_header) {
69  /* Skip extra picture header if present, not used at the moment. */
70  buf += picture_header;
71  len -= picture_header;
72  }
73 
74  if (len < 0) {
75  av_log(ctx, AV_LOG_ERROR, "Too short H.263 RTP packet\n");
76  return AVERROR_INVALIDDATA;
77  }
78 
79  if (av_new_packet(pkt, len + startcode)) {
80  av_log(ctx, AV_LOG_ERROR, "Out of memory\n");
81  return AVERROR(ENOMEM);
82  }
83  pkt->stream_index = st->index;
84  ptr = pkt->data;
85 
86  if (startcode) {
87  *ptr++ = 0;
88  *ptr++ = 0;
89  }
90  memcpy(ptr, buf, len);
91 
92  return 0;
93 }
94 
96  .enc_name = "H263-1998",
97  .codec_type = AVMEDIA_TYPE_VIDEO,
98  .codec_id = CODEC_ID_H263,
99  .parse_packet = h263_handle_packet,
100 };
101 
103  .enc_name = "H263-2000",
104  .codec_type = AVMEDIA_TYPE_VIDEO,
105  .codec_id = CODEC_ID_H263,
106  .parse_packet = h263_handle_packet,
107 };
108