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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. int ff_h263_handle_packet(AVFormatContext *ctx, PayloadContext *data,
  28.                           AVStream *st, AVPacket *pkt, uint32_t *timestamp,
  29.                           const uint8_t *buf, int len, uint16_t seq, int flags)
  30. {
  31.     uint8_t *ptr;
  32.     uint16_t header;
  33.     int startcode, vrc, picture_header;
  34.  
  35.     if (len < 2) {
  36.         av_log(ctx, AV_LOG_ERROR, "Too short H.263 RTP packet\n");
  37.         return AVERROR_INVALIDDATA;
  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.      */
  53.     header = AV_RB16(buf);
  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) {
  72.         av_log(ctx, AV_LOG_ERROR, "Too short H.263 RTP packet\n");
  73.         return AVERROR_INVALIDDATA;
  74.     }
  75.  
  76.     if (av_new_packet(pkt, len + startcode)) {
  77.         av_log(ctx, AV_LOG_ERROR, "Out of memory\n");
  78.         return AVERROR(ENOMEM);
  79.     }
  80.     pkt->stream_index = st->index;
  81.     ptr = pkt->data;
  82.  
  83.     if (startcode) {
  84.         *ptr++ = 0;
  85.         *ptr++ = 0;
  86.     }
  87.     memcpy(ptr, buf, len);
  88.  
  89.     return 0;
  90. }
  91.  
  92. RTPDynamicProtocolHandler ff_h263_1998_dynamic_handler = {
  93.     .enc_name         = "H263-1998",
  94.     .codec_type       = AVMEDIA_TYPE_VIDEO,
  95.     .codec_id         = AV_CODEC_ID_H263,
  96.     .need_parsing     = AVSTREAM_PARSE_FULL,
  97.     .parse_packet     = ff_h263_handle_packet,
  98. };
  99.  
  100. RTPDynamicProtocolHandler ff_h263_2000_dynamic_handler = {
  101.     .enc_name         = "H263-2000",
  102.     .codec_type       = AVMEDIA_TYPE_VIDEO,
  103.     .codec_id         = AV_CODEC_ID_H263,
  104.     .need_parsing     = AVSTREAM_PARSE_FULL,
  105.     .parse_packet     = ff_h263_handle_packet,
  106. };
  107.