Function msmpeg4_decode_picture_header

libavcodec/msmpeg4dec.c:363–527

}

static int msmpeg4_decode_picture_header(H263DecContext *const h)
{
    MSMP4DecContext *const ms = mpv_to_msmpeg4(h);
    int code;

    // at minimum one bit per macroblock is required at least in a valid frame,
    // we discard frames much smaller than this. Frames smaller than 1/8 of the
    // smallest "black/skip" frame generally contain not much recoverable content
    // while at the same time they have the highest computational requirements
    // per byte
    if (get_bits_left(&h->gb) * 8LL < (h->c.width+15)/16 * ((h->c.height+15)/16))
        return AVERROR_INVALIDDATA;

    if (h->c.msmpeg4_version == MSMP4_V1) {
        int start_code = get_bits_long(&h->gb, 32);
        if(start_code!=0x00000100){
            av_log(h->c.avctx, AV_LOG_ERROR, "invalid startcode\n");
            return -1;
        }

        skip_bits(&h->gb, 5); // frame number */
    }

    h->c.pict_type = get_bits(&h->gb, 2) + 1;
    if (h->c.pict_type != AV_PICTURE_TYPE_I &&
        h->c.pict_type != AV_PICTURE_TYPE_P){
        av_log(h->c.avctx, AV_LOG_ERROR, "invalid picture type\n");
        return -1;
    }
    h->c.chroma_qscale = h->c.qscale = get_bits(&h->gb, 5);
    if (h->c.qscale == 0) {
        av_log(h->c.avctx, AV_LOG_ERROR, "invalid qscale\n");
        return -1;
    }

    if (h->c.pict_type == AV_PICTURE_TYPE_I) {
        code = get_bits(&h->gb, 5);
        if (h->c.msmpeg4_version == MSMP4_V1) {
            if(code==0 || code>h->c.mb_height) {
                av_log(h->c.avctx, AV_LOG_ERROR, "invalid slice height %d\n", code);
                return -1;
            }

            h->slice_height = code;
        }else{
            /* 0x17: one slice, 0x18: two slices, ... */
            if (code < 0x17){
                av_log(h->c.avctx, AV_LOG_ERROR, "error, slice code was %X\n", code);
                return -1;
            }

            h->slice_height = h->c.mb_height / (code - 0x16);
        }

        switch (h->c.msmpeg4_version) {
        case MSMP4_V1:
        case MSMP4_V2:
            ms->rl_chroma_table_index = 2;