Function mpeg_decode_slice

libavcodec/mpeg12.c:1665–1884

* decodes a slice. MpegEncContext.mb_y must be set to the MB row from the startcode * @return DECODE_SLICE_ERROR if the slice is damaged * DECODE_SLICE_OK if this slice is ok */

 *         DECODE_SLICE_OK if this slice is ok<br>
 */
static int mpeg_decode_slice(Mpeg1Context *s1, int mb_y,
                             const uint8_t **buf, int buf_size)
{
    MpegEncContext *s = &s1->mpeg_enc_ctx;
    AVCodecContext *avctx= s->avctx;
    const int field_pic= s->picture_structure != PICT_FRAME;
    const int lowres= s->avctx->lowres;

    s->resync_mb_x=
    s->resync_mb_y= -1;

    assert(mb_y < s->mb_height);

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

    ff_mpeg1_clean_buffers(s);
    s->interlaced_dct = 0;

    s->qscale = get_qscale(s);

    if(s->qscale == 0){
        av_log(s->avctx, AV_LOG_ERROR, "qscale == 0\n");
        return -1;
    }

    /* extra slice info */
    while (get_bits1(&s->gb) != 0) {
        skip_bits(&s->gb, 8);
    }

    s->mb_x=0;

    if(mb_y==0 && s->codec_tag == AV_RL32("SLIF")){
        skip_bits1(&s->gb);
    }else{
        for(;;) {
            int code = get_vlc2(&s->gb, mbincr_vlc.table, MBINCR_VLC_BITS, 2);
            if (code < 0){
                av_log(s->avctx, AV_LOG_ERROR, "first mb_incr damaged\n");
                return -1;
            }
            if (code >= 33) {
                if (code == 33) {
                    s->mb_x += 33;
                }
                /* otherwise, stuffing, nothing to do */
            } else {
                s->mb_x += code;
                break;
            }
        }
    }

    if(s->mb_x >= (unsigned)s->mb_width){
        av_log(s->avctx, AV_LOG_ERROR, "initial skip overflow\n");
        return -1;
    }