Function ff_mpeg4_decode_studio_slice_header

libavcodec/mpeg4videodec.c:808–843

* Decode the next video packet. * @return <0 if something went wrong */

 * @return <0 if something went wrong
 */
int ff_mpeg4_decode_studio_slice_header(H263DecContext *const h)
{
    Mpeg4DecContext *const ctx = h263_to_mpeg4(h);
    GetBitContext *gb = &h->gb;
    unsigned vlc_len;
    uint16_t mb_num;

    if (get_bits_left(gb) >= 32 && get_bits_long(gb, 32) == SLICE_STARTCODE) {
        vlc_len = av_log2(h->c.mb_width * h->c.mb_height) + 1;
        mb_num = get_bits(gb, vlc_len);

        if (mb_num >= h->c.mb_num)
            return AVERROR_INVALIDDATA;

        h->c.mb_x = mb_num % h->c.mb_width;
        h->c.mb_y = mb_num / h->c.mb_width;

        if (ctx->shape != BIN_ONLY_SHAPE)
            h->c.qscale = mpeg_get_qscale(&h->gb, h->c.q_scale_type);

        if (get_bits1(gb)) {  /* slice_extension_flag */
            skip_bits1(gb);   /* intra_slice */
            skip_bits1(gb);   /* slice_VOP_id_enable */
            skip_bits(gb, 6); /* slice_VOP_id */
            while (get_bits1(gb)) /* extra_bit_slice */
                skip_bits(gb, 8); /* extra_information_slice */
        }

        reset_studio_dc_predictors(ctx);
    }
    else {
        return AVERROR_INVALIDDATA;
    }

    return 0;
}

/**
 * Get the average motion vector for a GMC MB.