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
26
30 {
33 int startcode, vrc, picture_header;
34
35 if (len < 2) {
38 }
39
40 /* Decode the 16 bit H.263+ payload header, as described in section
41 * 5.1 of RFC 4629. The fields of this header are:
42 * - 5 reserved bits, should be ignored.
43 * - One bit (P, startcode), indicating a picture start, picture segment
44 * start or video sequence end. If set, two zero bytes should be
45 * prepended to the payload.
46 * - One bit (V, vrc), indicating the presence of an 8 bit Video
47 * Redundancy Coding field after this 16 bit header.
48 * - 6 bits (PLEN, picture_header), the length (in bytes) of an extra
49 * picture header, following the VRC field.
50 * - 3 bits (PEBIT), the number of bits to ignore of the last byte
51 * of the extra picture header. (Not used at the moment.)
52 */
54 startcode = (header & 0x0400) >> 9;
55 vrc = header & 0x0200;
56 picture_header = (header & 0x01f8) >> 3;
57 buf += 2;
58 len -= 2;
59
60 if (vrc) {
61 /* Skip VRC header if present, not used at the moment. */
62 buf += 1;
63 len -= 1;
64 }
65 if (picture_header) {
66 /* Skip extra picture header if present, not used at the moment. */
67 buf += picture_header;
68 len -= picture_header;
69 }
70
71 if (len < 0) {
74 }
75
79 }
82
83 if (startcode) {
84 *ptr++ = 0;
85 *ptr++ = 0;
86 }
87 memcpy(ptr, buf, len);
88
89 return 0;
90 }
91
98 };
99
106 };