text: /*
   * VC-1 and WMV3 parser
   * Copyright (c) 2006-2007 Konstantin Shishkov
   * Partly based on vc9.c (c) 2005 Anonymous, Alex Beregszaszi, 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
   */
  
  /**
   * @file
   * VC-1 and WMV3 parser
   */
  
  #include "libavutil/attributes.h"
  #include "parser.h"
  #include "vc1.h"
  #include "get_bits.h"
  
  /** The maximum number of bytes of a sequence, entry point or
   *  frame header whose values we pay any attention to */
  #define UNESCAPED_THRESHOLD 37
  
  /** The maximum number of bytes of a sequence, entry point or
   *  frame header which must be valid memory (because they are
   *  used to update the bitstream cache in skip_bits() calls)
   */
  #define UNESCAPED_LIMIT 144
  
  typedef enum {
      NO_MATCH,
      ONE_ZERO,
      TWO_ZEROS,
      ONE
  } VC1ParseSearchState;
  
  typedef struct {
      ParseContext pc;
      VC1Context v;
      uint8_t prev_start_code;
      size_t bytes_to_skip;
      uint8_t unesc_buffer[UNESCAPED_LIMIT];
      size_t unesc_index;
      VC1ParseSearchState search_state;
  } VC1ParseContext;
  
  static void vc1_extract_header(AVCodecParserContext *s, AVCodecContext *avctx,
                                 const uint8_t *buf, int buf_size)
  {
      /* Parse the header we just finished unescaping */
      VC1ParseContext *vpc = s->priv_data;
      GetBitContext gb;
      int ret;
      vpc->v.s.avctx = avctx;
      vpc->v.parse_only = 1;
      init_get_bits(&gb, buf, buf_size * 8);
      switch (vpc->prev_start_code) {
      case VC1_CODE_SEQHDR & 0xFF:
          ff_vc1_decode_sequence_header(avctx, &vpc->v, &gb);
          break;
      case VC1_CODE_ENTRYPOINT & 0xFF:
          ff_vc1_decode_entry_point(avctx, &vpc->v, &gb);
          break;
      case VC1_CODE_FRAME & 0xFF:
          if(vpc->v.profile < PROFILE_ADVANCED)
              ret = ff_vc1_parse_frame_header    (&vpc->v, &gb);
          else
              ret = ff_vc1_parse_frame_header_adv(&vpc->v, &gb);
  
          if (ret < 0)
              break;
  
          /* keep AV_PICTURE_TYPE_BI internal to VC1 */
          if (vpc->v.s.pict_type == AV_PICTURE_TYPE_BI)
              s->pict_type = AV_PICTURE_TYPE_B;
          else
              s->pict_type = vpc->v.s.pict_type;
  
          if (avctx->ticks_per_frame > 1){
              // process pulldown flags
              s->repeat_pict = 1;
              // Pulldown flags are only valid when 'broadcast' has been set.
              // So ticks_per_frame will be 2
              if (vpc->v.rff){
                  // repeat field
                  s->repeat_pict = 2;
              }else if (vpc->v.rptfrm){
                  // repeat frames
                  s->repeat_pict = vpc->v.rptfrm * 2 + 1;
              }
          }else{
              s->repeat_pict = 0;
          }
  
          if (vpc->v.broadcast && vpc->v.interlace && !vpc->v.psf)
              s->field_order = vpc->v.tff ? AV_FIELD_TT : AV_FIELD_BB;
          else
              s->field_order = AV_FIELD_PROGRESSIVE;
  
          break;
      }
  }
  
  static int vc1_parse(AVCodecParserContext *s,
                             AVCodecContext *avctx,
                             const uint8_t **poutbuf, int *poutbuf_size,
                             const uint8_t *buf, int buf_size)
  {
      /* Here we do the searching for frame boundaries and headers at
       * the same time. Only a minimal amount at the start of each
       * header is unescaped. */
      VC1ParseContext *vpc = s->priv_data;
      int pic_found = vpc->pc.frame_start_found;
      uint8_t *unesc_buffer = vpc->unesc_buffer;
      size_t unesc_index = vpc->unesc_index;
      VC1ParseSearchState search_state = vpc->search_state;
      int start_code_found = 0;
      int next = END_NOT_FOUND;
      int i = vpc->bytes_to_skip;
  
      if (pic_found && buf_size == 0) {
          /* EOF considered as end of frame */
          memset(unesc_buffer + unesc_index, 0, UNESCAPED_THRESHOLD - unesc_index);
          vc1_extract_header(s, avctx, unesc_buffer, unesc_index);
          next = 0;
      }
      while (i < buf_size) {
          uint8_t b = 0;
          start_code_found = 0;
          while (i < buf_size && unesc_index < UNESCAPED_THRESHOLD) {
              b = buf[i++];
              unesc_buffer[unesc_index++] = b;
              if (search_state <= ONE_ZERO)
                  search_state = b ? NO_MATCH : search_state + 1;
              else if (search_state == TWO_ZEROS) {
                  if (b == 1)
                      search_state = ONE;
                  else if (b > 1) {
                      if (b == 3)
                          unesc_index--; // swallow emulation prevention byte
                      search_state = NO_MATCH;
                  }
              }
              else { // search_state == ONE
                  // Header unescaping terminates early due to detection of next start code
                  search_state = NO_MATCH;
                  start_code_found = 1;
                  break;
              }
          }
          if ((s->flags & PARSER_FLAG_COMPLETE_FRAMES) &&
                  unesc_index >= UNESCAPED_THRESHOLD &&
                  vpc->prev_start_code == (VC1_CODE_FRAME & 0xFF))
          {
              // No need to keep scanning the rest of the buffer for
              // start codes if we know it contains a complete frame and
              // we've already unescaped all we need of the frame header
              vc1_extract_header(s, avctx, unesc_buffer, unesc_index);
              break;
          }
          if (unesc_index >= UNESCAPED_THRESHOLD && !start_code_found) {
              while (i < buf_size) {
                  if (search_state == NO_MATCH) {
                      i += vpc->v.vc1dsp.startcode_find_candidate(buf + i, buf_size - i);
                      if (i < buf_size) {
                          search_state = ONE_ZERO;
                      }
                      i++;
                  } else {
                      b = buf[i++];
                      if (search_state == ONE_ZERO)
                          search_state = b ? NO_MATCH : TWO_ZEROS;
                      else if (search_state == TWO_ZEROS) {
                          if (b >= 1)
                              search_state = b == 1 ? ONE : NO_MATCH;
                      }
                      else { // search_state == ONE
                          search_state = NO_MATCH;
                          start_code_found = 1;
                          break;
                      }
                  }
              }
          }
          if (start_code_found) {
              vc1_extract_header(s, avctx, unesc_buffer, unesc_index);
  
              vpc->prev_start_code = b;
              unesc_index = 0;
  
              if (!(s->flags & PARSER_FLAG_COMPLETE_FRAMES)) {
                  if (!pic_found && (b == (VC1_CODE_FRAME & 0xFF) || b == (VC1_CODE_FIELD & 0xFF))) {
                      pic_found = 1;
                  }
                  else if (pic_found && b != (VC1_CODE_FIELD & 0xFF) && b != (VC1_CODE_SLICE & 0xFF)) {
                      next = i - 4;
                      pic_found = b == (VC1_CODE_FRAME & 0xFF);
                      break;
                  }
              }
          }
      }
  
      vpc->pc.frame_start_found = pic_found;
      vpc->unesc_index = unesc_index;
      vpc->search_state = search_state;
  
      if (s->flags & PARSER_FLAG_COMPLETE_FRAMES) {
          next = buf_size;
      } else {
          if (ff_combine_frame(&vpc->pc, next, &buf, &buf_size) < 0) {
              vpc->bytes_to_skip = 0;
              *poutbuf = NULL;
              *poutbuf_size = 0;
              return buf_size;
          }
      }
  
      /* If we return with a valid pointer to a combined frame buffer
       * then on the next call then we'll have been unhelpfully rewound
       * by up to 4 bytes (depending upon whether the start code
       * overlapped the input buffer, and if so by how much). We don't
       * want this: it will either cause spurious second detections of
       * the start code we've already seen, or cause extra bytes to be
       * inserted at the start of the unescaped buffer. */
      vpc->bytes_to_skip = 4;
      if (next < 0 && next != END_NOT_FOUND)
          vpc->bytes_to_skip += next;
  
      *poutbuf = buf;
      *poutbuf_size = buf_size;
      return next;
  }
  
  static int vc1_split(AVCodecContext *avctx,
                             const uint8_t *buf, int buf_size)
  {
      int i;
      uint32_t state= -1;
      int charged=0;
  
      for(i=0; i<buf_size; i++){
          state= (state<<8) | buf[i];
          if(IS_MARKER(state)){
              if(state == VC1_CODE_SEQHDR || state == VC1_CODE_ENTRYPOINT){
                  charged=1;
              }else if(charged){
                  return i-3;
              }
          }
      }
      return 0;
  }
  
  static av_cold int vc1_parse_init(AVCodecParserContext *s)
  {
      VC1ParseContext *vpc = s->priv_data;
      vpc->v.s.slice_context_count = 1;
      vpc->v.first_pic_header_flag = 1;
      vpc->prev_start_code = 0;
      vpc->bytes_to_skip = 0;
      vpc->unesc_index = 0;
      vpc->search_state = NO_MATCH;
      return ff_vc1_init_common(&vpc->v);
  }
  
  AVCodecParser ff_vc1_parser = {
  	.codec_ids      = { AV_CODEC_ID_VC1 },
      .priv_data_size = sizeof(VC1ParseContext),
      .parser_init    = vc1_parse_init,
      .parser_parse   = vc1_parse,
      .parser_close   = ff_parse_close,
      .split          = vc1_split,
  };
  