matroska_parse_block(MatroskaDemuxContext *matroska, uint8_t *data, int size,
                     int64_t pos, uint64_t cluster_time, uint64_t duration,
                     int is_keyframe, int is_bframe)
{
    int res = 0;
    int track;
    AVStream *st;
    AVPacket *pkt;
    uint8_t *origdata = data;
    int16_t block_time;
    uint32_t *lace_size = NULL;
    int n, flags, laces = 0;
    uint64_t num;
    int stream_index;
    /* first byte(s): tracknum */
    if ((n = matroska_ebmlnum_uint(data, size, &num)) < 0) {
        av_log(matroska->ctx, AV_LOG_ERROR, "EBML block data error\n");
        av_free(origdata);
        return res;
    }
    data += n;
    size -= n;
    /* fetch track from num */
    track = matroska_find_track_by_num(matroska, num);
    if (size <= 3 || track < 0 || track >= matroska->num_tracks) {
        av_log(matroska->ctx, AV_LOG_INFO,
               "Invalid stream %d or size %u\n", track, size);
        av_free(origdata);
        return res;
    }
    stream_index = matroska->tracks[track]->stream_index;
    if (stream_index < 0 || stream_index >= matroska->ctx->nb_streams) {
        av_free(origdata);
        return res;
    }
    st = matroska->ctx->streams[stream_index];
    if (st->discard >= AVDISCARD_ALL) {
        av_free(origdata);
        return res;
    }
    if (duration == AV_NOPTS_VALUE)
        duration = matroska->tracks[track]->default_duration / matroska->time_scale;
    /* block_time (relative to cluster time) */
    block_time = AV_RB16(data);
    data += 2;
    flags = *data++;
    size -= 3;
    if (is_keyframe == -1)
        is_keyframe = flags & 0x80 ? PKT_FLAG_KEY : 0;
    if (matroska->skip_to_keyframe) {
        if (!is_keyframe || st != matroska->skip_to_stream) {
            av_free(origdata);
            return res;
        }
        matroska->skip_to_keyframe = 0;
    }
    switch ((flags & 0x06) >> 1) {
        case 0x0: /* no lacing */
            laces = 1;
            lace_size = av_mallocz(sizeof(int));
            lace_size[0] = size;
            break;
        case 0x1: /* xiph lacing */
        case 0x2: /* fixed-size lacing */
        case 0x3: /* EBML lacing */
            assert(size>0); // size <=3 is checked before size-=3 above
            laces = (*data) + 1;
            data += 1;
            size -= 1;
            lace_size = av_mallocz(laces * sizeof(int));
            switch ((flags & 0x06) >> 1) {
                case 0x1: /* xiph lacing */ {
                    uint8_t temp;
                    uint32_t total = 0;
                    for (n = 0; res == 0 && n < laces - 1; n++) {
                        while (1) {
                            if (size == 0) {
                                res = -1;
                                break;
                            }
                            temp = *data;
                            lace_size[n] += temp;
                            data += 1;
                            size -= 1;
                            if (temp != 0xff)
                                break;
                        }
                        total += lace_size[n];
                    }
                    lace_size[n] = size - total;
                    break;
                }
                case 0x2: /* fixed-size lacing */
                    for (n = 0; n < laces; n++)
                        lace_size[n] = size / laces;
                    break;
                case 0x3: /* EBML lacing */ {
                    uint32_t total;
                    n = matroska_ebmlnum_uint(data, size, &num);
                    if (n < 0) {
                        av_log(matroska->ctx, AV_LOG_INFO,
                               "EBML block data error\n");
                        break;
                    }
                    data += n;
                    size -= n;
                    total = lace_size[0] = num;
                    for (n = 1; res == 0 && n < laces - 1; n++) {
                        int64_t snum;
                        int r;
                        r = matroska_ebmlnum_sint (data, size, &snum);
                        if (r < 0) {
                            av_log(matroska->ctx, AV_LOG_INFO,
                                   "EBML block data error\n");
                            break;
                        }
                        data += r;
                        size -= r;
                        lace_size[n] = lace_size[n - 1] + snum;
                        total += lace_size[n];
                    }
                    lace_size[n] = size - total;
                    break;
                }
            }
            break;
    }
    if (res == 0) {
        uint64_t timecode = AV_NOPTS_VALUE;
        if (cluster_time != (uint64_t)-1
            && (block_time >= 0 || cluster_time >= -block_time))
            timecode = cluster_time + block_time;
        for (n = 0; n < laces; n++) {
            if (st->codec->codec_id == CODEC_ID_RA_288 ||
                st->codec->codec_id == CODEC_ID_COOK ||
                st->codec->codec_id == CODEC_ID_ATRAC3) {
                MatroskaAudioTrack *audiotrack = (MatroskaAudioTrack *)matroska->tracks[track];
                int a = st->codec->block_align;
                int sps = audiotrack->sub_packet_size;
                int cfs = audiotrack->coded_framesize;
                int h = audiotrack->sub_packet_h;
                int y = audiotrack->sub_packet_cnt;
                int w = audiotrack->frame_size;
                int x;
                if (!audiotrack->pkt_cnt) {
                    if (st->codec->codec_id == CODEC_ID_RA_288)
                        for (x=0; x<h/2; x++)
                            memcpy(audiotrack->buf+x*2*w+y*cfs,
                                   data+x*cfs, cfs);
                    else
                        for (x=0; x<w/sps; x++)
                            memcpy(audiotrack->buf+sps*(h*x+((h+1)/2)*(y&1)+(y>>1)), data+x*sps, sps);
                    if (++audiotrack->sub_packet_cnt >= h) {
                        audiotrack->sub_packet_cnt = 0;
                        audiotrack->pkt_cnt = h*w / a;
                    }
                }
                while (audiotrack->pkt_cnt) {
                    pkt = av_mallocz(sizeof(AVPacket));
                    av_new_packet(pkt, a);
                    memcpy(pkt->data, audiotrack->buf
                           + a * (h*w / a - audiotrack->pkt_cnt--), a);
                    pkt->pos = pos;
                    pkt->stream_index = stream_index;
                    matroska_queue_packet(matroska, pkt);
                }
            } else {
                int result, offset = 0, ilen, olen, pkt_size = lace_size[n];
                uint8_t *pkt_data = data;
                if (matroska->tracks[track]->encoding_scope & 1) {
                    switch (matroska->tracks[track]->encoding_algo) {
                    case MATROSKA_TRACK_ENCODING_COMP_HEADERSTRIP:
                        offset = matroska->tracks[track]->encoding_settings_len;
                        break;
                    case MATROSKA_TRACK_ENCODING_COMP_LZO:
                        pkt_data = NULL;
                        do {
                            ilen = lace_size[n];
                            olen = pkt_size *= 3;
                            pkt_data = av_realloc(pkt_data,
                                                  pkt_size+LZO_OUTPUT_PADDING);
                            result = lzo1x_decode(pkt_data, &olen, data, &ilen);
                        } while (result==LZO_OUTPUT_FULL && pkt_size<10000000);
                        if (result) {
                            continue;
                        }
                        pkt_size -= olen;
                        break;
#ifdef CONFIG_ZLIB
                    case MATROSKA_TRACK_ENCODING_COMP_ZLIB: {
                        z_stream zstream = {0};
                        pkt_data = NULL;
                        if (inflateInit(&zstream) != Z_OK)
                            continue;
                        zstream.next_in = data;
                        zstream.avail_in = lace_size[n];
                        do {
                            pkt_size *= 3;
                            pkt_data = av_realloc(pkt_data, pkt_size);
                            zstream.avail_out = pkt_size - zstream.total_out;
                            zstream.next_out = pkt_data + zstream.total_out;
                            result = inflate(&zstream, Z_NO_FLUSH);
                        } while (result==Z_OK && pkt_size<10000000);
                        pkt_size = zstream.total_out;
                        inflateEnd(&zstream);
                        if (result != Z_STREAM_END) {
                            continue;
                        }
                        break;
                    }
#endif
#ifdef CONFIG_BZLIB
                    case MATROSKA_TRACK_ENCODING_COMP_BZLIB: {
                        bz_stream bzstream = {0};
                        pkt_data = NULL;
                        if (BZ2_bzDecompressInit(&bzstream, 0, 0) != BZ_OK)
                            continue;
                        bzstream.next_in = data;
                        bzstream.avail_in = lace_size[n];
                        do {
                            pkt_size *= 3;
                            pkt_data = av_realloc(pkt_data, pkt_size);
                            bzstream.avail_out = pkt_size - bzstream.total_out_lo32;
                            bzstream.next_out = pkt_data + bzstream.total_out_lo32;
                            result = BZ2_bzDecompress(&bzstream);
                        } while (result==BZ_OK && pkt_size<10000000);
                        pkt_size = bzstream.total_out_lo32;
                        BZ2_bzDecompressEnd(&bzstream);
                        if (result != BZ_STREAM_END) {
                            continue;
                        }
                        break;
                    }
#endif
                    }
                }
                pkt = av_mallocz(sizeof(AVPacket));
                /* XXX: prevent data copy... */
                if (av_new_packet(pkt, pkt_size+offset) < 0) {
                    av_free(pkt);
                    res = AVERROR(ENOMEM);
                    n = laces-1;
                    break;
                }
                if (offset)
                    memcpy (pkt->data, matroska->tracks[track]->encoding_settings, offset);
                memcpy (pkt->data+offset, pkt_data, pkt_size);
                if (n == 0)
                    pkt->flags = is_keyframe;
                pkt->stream_index = stream_index;
                pkt->pts = timecode;
                pkt->pos = pos;
                pkt->duration = duration;
                matroska_queue_packet(matroska, pkt);
            }
            if (timecode != AV_NOPTS_VALUE)
                timecode = duration ? timecode + duration : AV_NOPTS_VALUE;
            data += lace_size[n];
        }
    }
    av_free(lace_size);
    av_free(origdata);
    return res;
}