static int avs_read_packet(AVFormatContext * s, AVPacket * pkt)
{
    AvsFormat *avs = s->priv_data;
    int sub_type = 0, size = 0;
    AvsBlockType type = AVS_NONE;
    int palette_size = 0;
    uint8_t palette[4 + 3 * 256];
    int ret;

    if (avs->remaining_audio_size > 0)
        if (avs_read_audio_packet(s, pkt) > 0)
            return 0;

    while (1) {
        if (avs->remaining_frame_size <= 0) {
            if (!avio_rl16(s->pb))    /* found EOF */
                return AVERROR(EIO);
            avs->remaining_frame_size = avio_rl16(s->pb) - 4;
        }

        while (avs->remaining_frame_size > 0) {
            sub_type = avio_r8(s->pb);
            type = avio_r8(s->pb);
            size = avio_rl16(s->pb);
            if (size < 4)
                return AVERROR_INVALIDDATA;
            avs->remaining_frame_size -= size;

            switch (type) {
            case AVS_PALETTE:
                if (size - 4 > sizeof(palette))
                    return AVERROR_INVALIDDATA;
                ret = avio_read(s->pb, palette, size - 4);
                if (ret < size - 4)
                    return AVERROR(EIO);
                palette_size = size;
                break;

            case AVS_VIDEO:
                if (!avs->st_video) {
                    avs->st_video = av_new_stream(s, AVS_VIDEO);
                    if (avs->st_video == NULL)
                        return AVERROR(ENOMEM);
                    avs->st_video->codec->codec_type = AVMEDIA_TYPE_VIDEO;
                    avs->st_video->codec->codec_id = CODEC_ID_AVS;
                    avs->st_video->codec->width = avs->width;
                    avs->st_video->codec->height = avs->height;
                    avs->st_video->codec->bits_per_coded_sample=avs->bits_per_sample;
                    avs->st_video->nb_frames = avs->nb_frames;
                    avs->st_video->codec->time_base = (AVRational) {
                    1, avs->fps};
                }
                return avs_read_video_packet(s, pkt, type, sub_type, size,
                                             palette, palette_size);

            case AVS_AUDIO:
                if (!avs->st_audio) {
                    avs->st_audio = av_new_stream(s, AVS_AUDIO);
                    if (avs->st_audio == NULL)
                        return AVERROR(ENOMEM);
                    avs->st_audio->codec->codec_type = AVMEDIA_TYPE_AUDIO;
                }
                avs->remaining_audio_size = size - 4;
                size = avs_read_audio_packet(s, pkt);
                if (size != 0)
                    return size;
                break;

            default:
                avio_skip(s->pb, size - 4);
            }
        }
    }
}