*data_size=0;  if(buf==NULL && buf_size==0){ 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(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;}