text: /*
   * MPEG4 Video frame extraction
   * Copyright (c) 2003 Fabrice Bellard
   * Copyright (c) 2003 Michael Niedermayer
   *
   * 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
   */
  
  #define UNCHECKED_BITSTREAM_READER 1
  
  #include "internal.h"
  #include "parser.h"
  #include "mpegvideo.h"
  #include "mpeg4video.h"
  #include "mpeg4video_parser.h"
  
  struct Mp4vParseContext {
      ParseContext pc;
      Mpeg4DecContext dec_ctx;
      int first_picture;
  };
  
  int ff_mpeg4_find_frame_end(ParseContext *pc, const uint8_t *buf, int buf_size)
  {
      int vop_found, i;
      uint32_t state;
  
      vop_found = pc->frame_start_found;
      state     = pc->state;
  
      i = 0;
      if (!vop_found) {
          for (i = 0; i < buf_size; i++) {
              state = (state << 8) | buf[i];
              if (state == 0x1B6) {
                  i++;
                  vop_found = 1;
                  break;
              }
          }
      }
  
      if (vop_found) {
          /* EOF considered as end of frame */
          if (buf_size == 0)
              return 0;
          for (; i < buf_size; i++) {
              state = (state << 8) | buf[i];
              if ((state & 0xFFFFFF00) == 0x100) {
                  pc->frame_start_found = 0;
                  pc->state             = -1;
                  return i - 3;
              }
          }
      }
      pc->frame_start_found = vop_found;
      pc->state             = state;
      return END_NOT_FOUND;
  }
  
  /* XXX: make it use less memory */
  static int mpeg4_decode_header(AVCodecParserContext *s1, AVCodecContext *avctx,
                                 const uint8_t *buf, int buf_size)
  {
      struct Mp4vParseContext *pc = s1->priv_data;
      Mpeg4DecContext *dec_ctx = &pc->dec_ctx;
      MpegEncContext *s = &dec_ctx->m;
      GetBitContext gb1, *gb = &gb1;
      int ret;
  
      s->avctx               = avctx;
      s->current_picture_ptr = &s->current_picture;
  
      if (avctx->extradata_size && pc->first_picture) {
          init_get_bits(gb, avctx->extradata, avctx->extradata_size * 8);
          ret = ff_mpeg4_decode_picture_header(dec_ctx, gb);
          if (ret < 0)
              av_log(avctx, AV_LOG_WARNING, "Failed to parse extradata\n");
      }
  
      init_get_bits(gb, buf, 8 * buf_size);
      ret = ff_mpeg4_decode_picture_header(dec_ctx, gb);
      if (s->width && (!avctx->width || !avctx->height ||
                       !avctx->coded_width || !avctx->coded_height)) {
          ret = ff_set_dimensions(avctx, s->width, s->height);
          if (ret < 0)
              return ret;
      }
      if((s1->flags & PARSER_FLAG_USE_CODEC_TS) && s->avctx->time_base.den>0 && ret>=0){
          av_assert1(s1->pts == AV_NOPTS_VALUE);
          av_assert1(s1->dts == AV_NOPTS_VALUE);
  
          s1->pts = av_rescale_q(s->time, (AVRational){1, s->avctx->time_base.den}, (AVRational){1, 1200000});
      }
  
      s1->pict_type     = s->pict_type;
      pc->first_picture = 0;
      return ret;
  }
  
  static av_cold int mpeg4video_parse_init(AVCodecParserContext *s)
  {
      struct Mp4vParseContext *pc = s->priv_data;
  
      ff_mpeg4videodec_static_init();
  
      pc->first_picture           = 1;
      pc->dec_ctx.m.quant_precision     = 5;
      pc->dec_ctx.m.slice_context_count = 1;
      pc->dec_ctx.showed_packed_warning = 1;
      return 0;
  }
  
  static int mpeg4video_parse(AVCodecParserContext *s,
                              AVCodecContext *avctx,
                              const uint8_t **poutbuf, int *poutbuf_size,
                              const uint8_t *buf, int buf_size)
  {
      ParseContext *pc = s->priv_data;
      int next;
  
      if (s->flags & PARSER_FLAG_COMPLETE_FRAMES) {
          next = buf_size;
      } else {
          next = ff_mpeg4_find_frame_end(pc, buf, buf_size);
  
          if (ff_combine_frame(pc, next, &buf, &buf_size) < 0) {
              *poutbuf      = NULL;
              *poutbuf_size = 0;
              return buf_size;
          }
      }
      mpeg4_decode_header(s, avctx, buf, buf_size);
  
      *poutbuf      = buf;
      *poutbuf_size = buf_size;
      return next;
  }
  
  AVCodecParser ff_mpeg4video_parser = {
      .codec_ids      = { AV_CODEC_ID_MPEG4 },
      .priv_data_size = sizeof(struct Mp4vParseContext),
      .parser_init    = mpeg4video_parse_init,
      .parser_parse   = mpeg4video_parse,
      .parser_close   = ff_parse_close,
      .split          = ff_mpeg4video_split,
  };
  