libavformat/rtpdec_h263.c

   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
  26 static int h263_init(AVFormatContext *ctx, int st_index, PayloadContext *data)
  27 {
  28     if (st_index < 0)
  29         return 0;
  30     ctx->streams[st_index]->need_parsing = AVSTREAM_PARSE_FULL;
  31     return 0;
  32 }
  33
  34 int ff_h263_handle_packet(AVFormatContext *ctx, PayloadContext *data,
  35                           AVStream *st, AVPacket *pkt, uint32_t *timestamp,
  36                           const uint8_t *buf, int len, uint16_t seq, int flags)
  37 {
  38     uint8_t *ptr;
  39     uint16_t header;
  40     int startcode, vrc, picture_header;
  41
  42     if (len < 2) {
  43         av_log(ctx, AV_LOG_ERROR, "Too short H.263 RTP packet\n");
  44         return AVERROR_INVALIDDATA;
  45     }
  46
  47     /* Decode the 16 bit H.263+ payload header, as described in section
  48      * 5.1 of RFC 4629. The fields of this header are:
  49      * - 5 reserved bits, should be ignored.
  50      * - One bit (P, startcode), indicating a picture start, picture segment
  51      *   start or video sequence end. If set, two zero bytes should be
  52      *   prepended to the payload.
  53      * - One bit (V, vrc), indicating the presence of an 8 bit Video
  54      *   Redundancy Coding field after this 16 bit header.
  55      * - 6 bits (PLEN, picture_header), the length (in bytes) of an extra
  56      *   picture header, following the VRC field.
  57      * - 3 bits (PEBIT), the number of bits to ignore of the last byte
  58      *   of the extra picture header. (Not used at the moment.)
  59      */
  60     header = AV_RB16(buf);
  61     startcode      = (header & 0x0400) >> 9;
  62     vrc            =  header & 0x0200;
  63     picture_header = (header & 0x01f8) >> 3;
  64     buf += 2;
  65     len -= 2;
  66
  67     if (vrc) {
  68         /* Skip VRC header if present, not used at the moment. */
  69         buf += 1;
  70         len -= 1;
  71     }
  72     if (picture_header) {
  73         /* Skip extra picture header if present, not used at the moment. */
  74         buf += picture_header;
  75         len -= picture_header;
  76     }
  77
  78     if (len < 0) {
  79         av_log(ctx, AV_LOG_ERROR, "Too short H.263 RTP packet\n");
  80         return AVERROR_INVALIDDATA;
  81     }
  82
  83     if (av_new_packet(pkt, len + startcode)) {
  84         av_log(ctx, AV_LOG_ERROR, "Out of memory\n");
  85         return AVERROR(ENOMEM);
  86     }
  87     pkt->stream_index = st->index;
  88     ptr = pkt->data;
  89
  90     if (startcode) {
  91         *ptr++ = 0;
  92         *ptr++ = 0;
  93     }
  94     memcpy(ptr, buf, len);
  95
  96     return 0;
  97 }
  98
  99 RTPDynamicProtocolHandler ff_h263_1998_dynamic_handler = {
 100     .enc_name         = "H263-1998",
 101     .codec_type       = AVMEDIA_TYPE_VIDEO,
 102     .codec_id         = AV_CODEC_ID_H263,
 103     .init             = h263_init,
 104     .parse_packet     = ff_h263_handle_packet,
 105 };
 106
 107 RTPDynamicProtocolHandler ff_h263_2000_dynamic_handler = {
 108     .enc_name         = "H263-2000",
 109     .codec_type       = AVMEDIA_TYPE_VIDEO,
 110     .codec_id         = AV_CODEC_ID_H263,
 111     .init             = h263_init,
 112     .parse_packet     = ff_h263_handle_packet,
 113 };