svq1dec.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 (result != 0)
    return result;

  /* predict and decode motion vector (1) */
  pmv[0] = &mv;
  if (y == 0) {
    pmv[1] =
    pmv[2] = pmv[0];
  }
  else {
    pmv[1] = &motion[(x / 8) + 3];
  }
  result = svq1_decode_motion_vector (bitbuf, &motion[0], pmv);

  if (result != 0)
    return result;

  /* predict and decode motion vector (2) */
  pmv[1] = &motion[0];
  pmv[2] = &motion[(x / 8) + 1];

  result = svq1_decode_motion_vector (bitbuf, &motion[(x / 8) + 2], pmv);

  if (result != 0)
    return result;

  /* predict and decode motion vector (3) */
  pmv[2] = &motion[(x / 8) + 2];
  pmv[3] = &motion[(x / 8) + 3];

  result = svq1_decode_motion_vector (bitbuf, pmv[3], pmv);

  if (result != 0)
    return result;

  /* form predictions */
  for (i=0; i < 4; i++) {
    int mvx= pmv[i]->x + (i&1)*16;
    int mvy= pmv[i]->y + (i>>1)*16;

    ///XXX /FIXME clipping or padding?
    if(y + (mvy >> 1)<0)
       mvy= 0;
    if(x + (mvx >> 1)<0)
       mvx= 0;

#if 0
  int w= (s->width+15)&~15;
  int h= (s->height+15)&~15;
  if(x + (mvx >> 1)<0 || y + (mvy >> 1)<0 || x + (mvx >> 1) + 8 > w || y + (mvy >> 1) + 8> h)
      av_log(s->avctx, AV_LOG_INFO, "%d %d %d %d\n", x, y, x + (mvx >> 1), y + (mvy >> 1));
#endif
    src = &previous[(x + (mvx >> 1)) + (y + (mvy >> 1))*pitch];
    dst = current;

    s->dsp.put_pixels_tab[1][((mvy & 1) << 1) | (mvx & 1)](dst,src,pitch,8);

    /* select next block */
    if (i & 1) {
      current  += 8*(pitch - 1);
    } else {
      current  += 8;
    }
  }

  return 0;
}

static int svq1_decode_delta_block (MpegEncContext *s, GetBitContext *bitbuf,
                        uint8_t *current, uint8_t *previous, int pitch,
                        svq1_pmv_t *motion, int x, int y) {
  uint32_t block_type;
  int      result = 0;

  /* get block type */
  block_type = get_vlc2(bitbuf, svq1_block_type.table, 2, 2);

  /* reset motion vectors */
  if (block_type == SVQ1_BLOCK_SKIP || block_type == SVQ1_BLOCK_INTRA) {
    motion[0].x                 =
    motion[0].y                 =
    motion[(x / 8) + 2].x =
    motion[(x / 8) + 2].y =
    motion[(x / 8) + 3].x =
    motion[(x / 8) + 3].y = 0;
  }

  switch (block_type) {
  case SVQ1_BLOCK_SKIP:
    svq1_skip_block (current, previous, pitch, x, y);
    break;

  case SVQ1_BLOCK_INTER:
    result = svq1_motion_inter_block (s, bitbuf, current, previous, pitch, motion, x, y);

    if (result != 0)
    {
#ifdef DEBUG_SVQ1
    av_log(s->avctx, AV_LOG_INFO, "Error in svq1_motion_inter_block %i\n",result);
#endif
      break;
    }
    result = svq1_decode_block_non_intra (bitbuf, current, pitch);
    break;

  case SVQ1_BLOCK_INTER_4V:
    result = svq1_motion_inter_4v_block (s, bitbuf, current, previous, pitch, motion, x, y);

    if (result != 0)
    {
#ifdef DEBUG_SVQ1
    av_log(s->avctx, AV_LOG_INFO, "Error in svq1_motion_inter_4v_block %i\n",result);
#endif
      break;
    }
    result = svq1_decode_block_non_intra (bitbuf, current, pitch);
    break;

  case SVQ1_BLOCK_INTRA:
    result = svq1_decode_block_intra (bitbuf, current, pitch);
    break;
  }

  return result;
}

static uint16_t svq1_packet_checksum (uint8_t *data, int length, int value) {
  int i;

  for (i=0; i < length; i++) {
    value = checksum_table[data[i] ^ (value >> 8)] ^ ((value & 0xFF) << 8);
  }

  return value;
}

static void svq1_parse_string (GetBitContext *bitbuf, uint8_t *out) {
  uint8_t seed;
  int     i;

  out[0] = get_bits (bitbuf, 8);

  seed = string_table[out[0]];

  for (i=1; i <= out[0]; i++) {
    out[i] = get_bits (bitbuf, 8) ^ seed;
    seed   = string_table[out[i] ^ seed];
  }
}

static int svq1_decode_frame_header (GetBitContext *bitbuf,MpegEncContext *s) {
  int frame_size_code;
  int temporal_reference;

  temporal_reference = get_bits (bitbuf, 8);

  /* frame type */
  s->pict_type= get_bits (bitbuf, 2)+1;
  if(s->pict_type==4)
      return -1;

  if (s->pict_type == I_TYPE) {

    /* unknown fields */
    if (s->f_code == 0x50 || s->f_code == 0x60) {
      int csum = get_bits (bitbuf, 16);

      csum = svq1_packet_checksum ((uint8_t *)bitbuf->buffer, bitbuf->size_in_bits>>3, csum);

//      av_log(s->avctx, AV_LOG_INFO, "%s checksum (%02x) for packet data\n",
//              (csum == 0) ? "correct" : "incorrect", csum);
    }

    if ((s->f_code ^ 0x10) >= 0x50) {
      uint8_t msg[256];

      svq1_parse_string (bitbuf, msg);

      av_log(s->avctx, AV_LOG_INFO, "embedded message: \"%s\"\n", (char *) msg);
    }

    skip_bits (bitbuf, 2);
    skip_bits (bitbuf, 2);
    skip_bits1 (bitbuf);

    /* load frame size */
    frame_size_code = get_bits (bitbuf, 3);

    if (frame_size_code == 7) {
      /* load width, height (12 bits each) */
      s->width = get_bits (bitbuf, 12);
      s->height = get_bits (bitbuf, 12);

      if (!s->width || !s->height)
        return -1;
    } else {
      /* get width, height from table */
      s->width = ff_svq1_frame_size_table[frame_size_code].width;
      s->height = ff_svq1_frame_size_table[frame_size_code].height;
    }
  }

  /* unknown fields */
  if (get_bits1 (bitbuf) == 1) {
    skip_bits1 (bitbuf);       /* use packet checksum if (1) */
    skip_bits1 (bitbuf);       /* component checksums after image data if (1) */

    if (get_bits (bitbuf, 2) != 0)
      return -1;
  }

  if (get_bits1 (bitbuf) == 1) {
    skip_bits1 (bitbuf);
    skip_bits (bitbuf, 4);
    skip_bits1 (bitbuf);
    skip_bits (bitbuf, 2);

    while (get_bits1 (bitbuf) == 1) {
      skip_bits (bitbuf, 8);
    }
  }

  return 0;
}

static int svq1_decode_frame(AVCodecContext *avctx,
                             void *data, int *data_size,
                             uint8_t *buf, int buf_size)
{
  MpegEncContext *s=avctx->priv_data;
  uint8_t        *current, *previous;
  int             result, i, x, y, width, height;
  AVFrame *pict = data;

  /* initialize bit buffer */
  init_get_bits(&s->gb,buf,buf_size*8);

  /* decode frame header */
  s->f_code = get_bits (&s->gb, 22);

  if ((s->f_code & ~0x70) || !(s->f_code & 0x60))
    return -1;

  /* swap some header bytes (why?) */
  if (s->f_code != 0x20) {
    uint32_t *src = (uint32_t *) (buf + 4);

    for (i=0; i < 4; i++) {
      src[i] = ((src[i] << 16) | (src[i] >> 16)) ^ src[7 - i];
    }
  }

  result = svq1_decode_frame_header (&s->gb, s);

  if (result != 0)
  {
#ifdef DEBUG_SVQ1
    av_log(s->avctx, AV_LOG_INFO, "Error in svq1_decode_frame_header %i\n",result);
#endif
    return result;
  }

  //FIXME this avoids some confusion for "B frames" without 2 references
  //this should be removed after libavcodec can handle more flexible picture types & ordering
  if(s->pict_type==B_TYPE && s->last_picture_ptr==NULL) return buf_size;

  if(avctx->hurry_up && s->pict_type==B_TYPE) return buf_size;
  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 buf_size;

  if(MPV_frame_start(s, avctx) < 0)
      return -1;

  /* decode y, u and v components */
  for (i=0; i < 3; i++) {
    int linesize;
    if (i == 0) {
      width  = (s->width+15)&~15;
      height = (s->height+15)&~15;
      linesize= s->linesize;
    } else {
      if(s->flags&CODEC_FLAG_GRAY) break;
      width  = (s->width/4+15)&~15;
      height = (s->height/4+15)&~15;
      linesize= s->uvlinesize;
    }

    current  = s->current_picture.data[i];

    if(s->pict_type==B_TYPE){
        previous = s->next_picture.data[i];
    }else{
        previous = s->last_picture.data[i];
    }

    if (s->pict_type == I_TYPE) {
      /* keyframe */
      for (y=0; y < height; y+=16) {
        for (x=0; x < width; x+=16) {
          result = svq1_decode_block_intra (&s->gb, &current[x], linesize);
          if (result != 0)
          {
//#ifdef DEBUG_SVQ1
            av_log(s->avctx, AV_LOG_INFO, "Error in svq1_decode_block %i (keyframe)\n",result);
//#endif
            return result;
          }
        }
        current += 16*linesize;
      }
    } else {
      svq1_pmv_t pmv[width/8+3];
      /* delta frame */
      memset (pmv, 0, ((width / 8) + 3) * sizeof(svq1_pmv_t));

      for (y=0; y < height; y+=16) {
        for (x=0; x < width; x+=16) {
          result = svq1_decode_delta_block (s, &s->gb, &current[x], previous,
                                            linesize, pmv, x, y);
          if (result != 0)
          {
#ifdef DEBUG_SVQ1
    av_log(s->avctx, AV_LOG_INFO, "Error in svq1_decode_delta_block %i\n",result);
#endif
            return result;
          }
        }

        pmv[0].x =
        pmv[0].y = 0;

        current += 16*linesize;
      }
    }
  }

  *pict = *(AVFrame*)&s->current_picture;


  MPV_frame_end(s);

  *data_size=sizeof(AVFrame);
  return buf_size;
}

static int svq1_decode_init(AVCodecContext *avctx)
{
    MpegEncContext *s = avctx->priv_data;
    int i;

    MPV_decode_defaults(s);

    s->avctx = avctx;
    s->width = (avctx->width+3)&~3;
    s->height = (avctx->height+3)&~3;
    s->codec_id= avctx->codec->id;
    avctx->pix_fmt = PIX_FMT_YUV410P;
    avctx->has_b_frames= 1; // not true, but DP frames and these behave like unidirectional b frames
    s->flags= avctx->flags;
    if (MPV_common_init(s) < 0) return -1;

    init_vlc(&svq1_block_type, 2, 4,
        &ff_svq1_block_type_vlc[0][1], 2, 1,
        &ff_svq1_block_type_vlc[0][0], 2, 1, 1);

    init_vlc(&svq1_motion_component, 7, 33,
        &mvtab[0][1], 2, 1,
        &mvtab[0][0], 2, 1, 1);

    for (i = 0; i < 6; i++) {
        init_vlc(&svq1_intra_multistage[i], 3, 8,
            &ff_svq1_intra_multistage_vlc[i][0][1], 2, 1,
            &ff_svq1_intra_multistage_vlc[i][0][0], 2, 1, 1);
        init_vlc(&svq1_inter_multistage[i], 3, 8,
            &ff_svq1_inter_multistage_vlc[i][0][1], 2, 1,
            &ff_svq1_inter_multistage_vlc[i][0][0], 2, 1, 1);
    }

    init_vlc(&svq1_intra_mean, 8, 256,
        &ff_svq1_intra_mean_vlc[0][1], 4, 2,
        &ff_svq1_intra_mean_vlc[0][0], 4, 2, 1);

    init_vlc(&svq1_inter_mean, 9, 512,
        &ff_svq1_inter_mean_vlc[0][1], 4, 2,
        &ff_svq1_inter_mean_vlc[0][0], 4, 2, 1);

    return 0;
}

static int svq1_decode_end(AVCodecContext *avctx)
{
    MpegEncContext *s = avctx->priv_data;

    MPV_common_end(s);
    return 0;
}


AVCodec svq1_decoder = {
    "svq1",
    CODEC_TYPE_VIDEO,
    CODEC_ID_SVQ1,
    sizeof(MpegEncContext),
    svq1_decode_init,
    NULL,
    svq1_decode_end,
    svq1_decode_frame,
    CODEC_CAP_DR1,
    .flush= ff_mpeg_flush,
    .pix_fmts= (enum PixelFormat[]){PIX_FMT_YUV410P, -1},
};