svq3.c

ffmpeg的完整源代码和作者自己写的文档。不但有在Linux的工程哦

      if ((cbp & 0x20)) {
        for (i=0; i < 8; i++) {
          h->non_zero_count_cache[ scan8[16+i] ] = 1;

          if (svq3_decode_block (&s->gb, &h->mb[16*(16 + i)], 1, 1)){
            av_log(h->s.avctx, AV_LOG_ERROR, "error while decoding chroma ac block\n");
            return -1;
          }
        }
      }
    }
  }

  s->current_picture.mb_type[mb_xy] = mb_type;

  if (IS_INTRA(mb_type)) {
    h->chroma_pred_mode = check_intra_pred_mode (h, DC_PRED8x8);
  }

  return 0;
}

static int svq3_decode_slice_header (H264Context *h) {
  MpegEncContext *const s = (MpegEncContext *) h;
  const int mb_xy = s->mb_x + s->mb_y*s->mb_stride;
  int i, header;

  header = get_bits (&s->gb, 8);

  if (((header & 0x9F) != 1 && (header & 0x9F) != 2) || (header & 0x60) == 0) {
    /* TODO: what? */
    av_log(h->s.avctx, AV_LOG_ERROR, "unsupported slice header (%02X)\n", header);
    return -1;
  } else {
    int length = (header >> 5) & 3;

    h->next_slice_index = get_bits_count(&s->gb) + 8*show_bits (&s->gb, 8*length) + 8*length;

    if (h->next_slice_index > s->gb.size_in_bits){
      av_log(h->s.avctx, AV_LOG_ERROR, "slice after bitstream end\n");
      return -1;
    }

    s->gb.size_in_bits = h->next_slice_index - 8*(length - 1);
    skip_bits(&s->gb, 8);

    if (length > 0) {
      memcpy ((uint8_t *) &s->gb.buffer[get_bits_count(&s->gb) >> 3],
             &s->gb.buffer[s->gb.size_in_bits >> 3], (length - 1));
    }
  }

  if ((i = svq3_get_ue_golomb (&s->gb)) == INVALID_VLC || i >= 3){
    av_log(h->s.avctx, AV_LOG_ERROR, "illegal slice type %d \n", i);
    return -1;
  }

  h->slice_type = golomb_to_pict_type[i];

  if ((header & 0x9F) == 2) {
    i = (s->mb_num < 64) ? 6 : (1 + av_log2 (s->mb_num - 1));
    s->mb_skip_run = get_bits (&s->gb, i) - (s->mb_x + (s->mb_y * s->mb_width));
  } else {
    skip_bits1 (&s->gb);
    s->mb_skip_run = 0;
  }

  h->slice_num = get_bits (&s->gb, 8);
  s->qscale = get_bits (&s->gb, 5);
  s->adaptive_quant = get_bits1 (&s->gb);

  /* unknown fields */
  skip_bits1 (&s->gb);

  if (h->unknown_svq3_flag) {
    skip_bits1 (&s->gb);
  }

  skip_bits1 (&s->gb);
  skip_bits (&s->gb, 2);

  while (get_bits1 (&s->gb)) {
    skip_bits (&s->gb, 8);
  }

  /* reset intra predictors and invalidate motion vector references */
  if (s->mb_x > 0) {
    memset (h->intra4x4_pred_mode[mb_xy - 1], -1, 4*sizeof(int8_t));
    memset (h->intra4x4_pred_mode[mb_xy - s->mb_x], -1, 8*sizeof(int8_t)*s->mb_x);
  }
  if (s->mb_y > 0) {
    memset (h->intra4x4_pred_mode[mb_xy - s->mb_stride], -1, 8*sizeof(int8_t)*(s->mb_width - s->mb_x));

    if (s->mb_x > 0) {
      h->intra4x4_pred_mode[mb_xy - s->mb_stride - 1][3] = -1;
    }
  }

  return 0;
}

static int svq3_decode_frame (AVCodecContext *avctx,
                              void *data, int *data_size,
                              uint8_t *buf, int buf_size) {
  MpegEncContext *const s = avctx->priv_data;
  H264Context *const h = avctx->priv_data;
  int m, mb_type;
  unsigned char *extradata;
  unsigned int size;

  s->flags = avctx->flags;
  s->flags2 = avctx->flags2;
  s->unrestricted_mv = 1;

  if (!s->context_initialized) {
    s->width = avctx->width;
    s->height = avctx->height;
    h->halfpel_flag = 1;
    h->thirdpel_flag = 1;
    h->unknown_svq3_flag = 0;
    h->chroma_qp[0] = h->chroma_qp[1] = 4;

    if (MPV_common_init (s) < 0)
      return -1;

    h->b_stride = 4*s->mb_width;

    alloc_tables (h);

    /* prowl for the "SEQH" marker in the extradata */
    extradata = (unsigned char *)avctx->extradata;
    for (m = 0; m < avctx->extradata_size; m++) {
      if (!memcmp (extradata, "SEQH", 4))
        break;
      extradata++;
    }

    /* if a match was found, parse the extra data */
    if (extradata && !memcmp (extradata, "SEQH", 4)) {

      GetBitContext gb;

      size = AV_RB32(&extradata[4]);
      init_get_bits (&gb, extradata + 8, size*8);

      /* 'frame size code' and optional 'width, height' */
      if (get_bits (&gb, 3) == 7) {
        skip_bits (&gb, 12);
        skip_bits (&gb, 12);
      }

      h->halfpel_flag = get_bits1 (&gb);
      h->thirdpel_flag = get_bits1 (&gb);

      /* unknown fields */
      skip_bits1 (&gb);
      skip_bits1 (&gb);
      skip_bits1 (&gb);
      skip_bits1 (&gb);

      s->low_delay = get_bits1 (&gb);

      /* unknown field */
      skip_bits1 (&gb);

      while (get_bits1 (&gb)) {
        skip_bits (&gb, 8);
      }

      h->unknown_svq3_flag = get_bits1 (&gb);
      avctx->has_b_frames = !s->low_delay;
    }
  }

  /* special case for last picture */
  if (buf_size == 0) {
    if (s->next_picture_ptr && !s->low_delay) {
      *(AVFrame *) data = *(AVFrame *) &s->next_picture;
      *data_size = sizeof(AVFrame);
    }
    return 0;
  }

  init_get_bits (&s->gb, buf, 8*buf_size);

  s->mb_x = s->mb_y = 0;

  if (svq3_decode_slice_header (h))
    return -1;

  s->pict_type = h->slice_type;
  s->picture_number = h->slice_num;

  if(avctx->debug&FF_DEBUG_PICT_INFO){
      av_log(h->s.avctx, AV_LOG_DEBUG, "%c hpel:%d, tpel:%d aqp:%d qp:%d\n",
      av_get_pict_type_char(s->pict_type), h->halfpel_flag, h->thirdpel_flag,
      s->adaptive_quant, s->qscale
      );
  }

  /* for hurry_up==5 */
  s->current_picture.pict_type = s->pict_type;
  s->current_picture.key_frame = (s->pict_type == I_TYPE);

  /* Skip B-frames if we do not have reference frames. */
  if (s->last_picture_ptr == NULL && s->pict_type == B_TYPE) return 0;
  /* Skip B-frames if we are in a hurry. */
  if (avctx->hurry_up && s->pict_type == B_TYPE) return 0;
  /* Skip everything if we are in a hurry >= 5. */
  if (avctx->hurry_up >= 5) return 0;
  if(  (avctx->skip_frame >= AVDISCARD_NONREF && s->pict_type==B_TYPE)
     ||(avctx->skip_frame >= AVDISCARD_NONKEY && s->pict_type!=I_TYPE)
     || avctx->skip_frame >= AVDISCARD_ALL)
      return 0;

  if (s->next_p_frame_damaged) {
    if (s->pict_type == B_TYPE)
      return 0;
    else
      s->next_p_frame_damaged = 0;
  }

  if (frame_start (h) < 0)
    return -1;

  if (s->pict_type == B_TYPE) {
    h->frame_num_offset = (h->slice_num - h->prev_frame_num);

    if (h->frame_num_offset < 0) {
      h->frame_num_offset += 256;
    }
    if (h->frame_num_offset == 0 || h->frame_num_offset >= h->prev_frame_num_offset) {
      av_log(h->s.avctx, AV_LOG_ERROR, "error in B-frame picture id\n");
      return -1;
    }
  } else {
    h->prev_frame_num = h->frame_num;
    h->frame_num = h->slice_num;
    h->prev_frame_num_offset = (h->frame_num - h->prev_frame_num);

    if (h->prev_frame_num_offset < 0) {
      h->prev_frame_num_offset += 256;
    }
  }

  for(m=0; m<2; m++){
    int i;
    for(i=0; i<4; i++){
      int j;
      for(j=-1; j<4; j++)
        h->ref_cache[m][scan8[0] + 8*i + j]= 1;
      if(i<3)
        h->ref_cache[m][scan8[0] + 8*i + j]= PART_NOT_AVAILABLE;
    }
  }

  for (s->mb_y=0; s->mb_y < s->mb_height; s->mb_y++) {
    for (s->mb_x=0; s->mb_x < s->mb_width; s->mb_x++) {

      if ( (get_bits_count(&s->gb) + 7) >= s->gb.size_in_bits &&
          ((get_bits_count(&s->gb) & 7) == 0 || show_bits (&s->gb, (-get_bits_count(&s->gb) & 7)) == 0)) {

        skip_bits(&s->gb, h->next_slice_index - get_bits_count(&s->gb));
        s->gb.size_in_bits = 8*buf_size;

        if (svq3_decode_slice_header (h))
          return -1;

        /* TODO: support s->mb_skip_run */
      }

      mb_type = svq3_get_ue_golomb (&s->gb);

      if (s->pict_type == I_TYPE) {
        mb_type += 8;
      } else if (s->pict_type == B_TYPE && mb_type >= 4) {
        mb_type += 4;
      }
      if (mb_type > 33 || svq3_decode_mb (h, mb_type)) {
        av_log(h->s.avctx, AV_LOG_ERROR, "error while decoding MB %d %d\n", s->mb_x, s->mb_y);
        return -1;
      }

      if (mb_type != 0) {
        hl_decode_mb (h);
      }

      if (s->pict_type != B_TYPE && !s->low_delay) {
        s->current_picture.mb_type[s->mb_x + s->mb_y*s->mb_stride] =
                        (s->pict_type == P_TYPE && mb_type < 8) ? (mb_type - 1) : -1;
      }
    }

    ff_draw_horiz_band(s, 16*s->mb_y, 16);
  }

  MPV_frame_end(s);

  if (s->pict_type == B_TYPE || s->low_delay) {
    *(AVFrame *) data = *(AVFrame *) &s->current_picture;
  } else {
    *(AVFrame *) data = *(AVFrame *) &s->last_picture;
  }

  avctx->frame_number = s->picture_number - 1;

  /* Do not output the last pic after seeking. */
  if (s->last_picture_ptr || s->low_delay) {
    *data_size = sizeof(AVFrame);
  }

  return buf_size;
}


AVCodec svq3_decoder = {
    "svq3",
    CODEC_TYPE_VIDEO,
    CODEC_ID_SVQ3,
    sizeof(H264Context),
    decode_init,
    NULL,
    decode_end,
    svq3_decode_frame,
    CODEC_CAP_DRAW_HORIZ_BAND | CODEC_CAP_DR1 | CODEC_CAP_DELAY,
};