/*
  * RTP H.263 Depacketizer, RFC 4629
  * Copyright (c) 2010 Martin Storsjo
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
 #include "avformat.h"

 #include "rtpdec_formats.h"

 #include "libavutil/attributes.h"

 #include "libavutil/intreadwrite.h"
 

 int ff_h263_handle_packet(AVFormatContext *ctx, PayloadContext *data,
                           AVStream *st, AVPacket *pkt, uint32_t *timestamp,

                           const uint8_t *buf, int len, uint16_t seq, int flags)

 {
     uint8_t *ptr;
     uint16_t header;
     int startcode, vrc, picture_header;
 
     if (len < 2) {
         av_log(ctx, AV_LOG_ERROR, "Too short H.263 RTP packet\n");
         return AVERROR_INVALIDDATA;
     }
 
     /* Decode the 16 bit H.263+ payload header, as described in section
      * 5.1 of RFC 4629. The fields of this header are:
      * - 5 reserved bits, should be ignored.
      * - One bit (P, startcode), indicating a picture start, picture segment
      *   start or video sequence end. If set, two zero bytes should be
      *   prepended to the payload.
      * - One bit (V, vrc), indicating the presence of an 8 bit Video
      *   Redundancy Coding field after this 16 bit header.
      * - 6 bits (PLEN, picture_header), the length (in bytes) of an extra
      *   picture header, following the VRC field.
      * - 3 bits (PEBIT), the number of bits to ignore of the last byte
      *   of the extra picture header. (Not used at the moment.)
      */
     header = AV_RB16(buf);
     startcode      = (header & 0x0400) >> 9;
     vrc            =  header & 0x0200;
     picture_header = (header & 0x01f8) >> 3;
     buf += 2;
     len -= 2;
 
     if (vrc) {
         /* Skip VRC header if present, not used at the moment. */
         buf += 1;
         len -= 1;
     }
     if (picture_header) {
         /* Skip extra picture header if present, not used at the moment. */
         buf += picture_header;
         len -= picture_header;
     }
 
     if (len < 0) {
         av_log(ctx, AV_LOG_ERROR, "Too short H.263 RTP packet\n");
         return AVERROR_INVALIDDATA;
     }
 
     if (av_new_packet(pkt, len + startcode)) {
         av_log(ctx, AV_LOG_ERROR, "Out of memory\n");

         return AVERROR(ENOMEM);

     }
     pkt->stream_index = st->index;
     ptr = pkt->data;
 
     if (startcode) {
         *ptr++ = 0;
         *ptr++ = 0;
     }
     memcpy(ptr, buf, len);
 
     return 0;
 }
 
 RTPDynamicProtocolHandler ff_h263_1998_dynamic_handler = {
     .enc_name         = "H263-1998",

     .codec_type       = AVMEDIA_TYPE_VIDEO,

     .codec_id         = AV_CODEC_ID_H263,

     .need_parsing     = AVSTREAM_PARSE_FULL,

     .parse_packet     = ff_h263_handle_packet,

 };
 
 RTPDynamicProtocolHandler ff_h263_2000_dynamic_handler = {
     .enc_name         = "H263-2000",

     .codec_type       = AVMEDIA_TYPE_VIDEO,

     .codec_id         = AV_CODEC_ID_H263,

     .need_parsing     = AVSTREAM_PARSE_FULL,

     .parse_packet     = ff_h263_handle_packet,

 };