static int avi_read_idx1(AVFormatContext *s, int size)
{
    AVIContext *avi = s->priv_data;
    AVIOContext *pb = s->pb;
    int nb_index_entries, i;
    AVStream *st;
    AVIStream *ast;
    unsigned int index, tag, flags, pos, len, first_packet = 1;
    unsigned last_pos= -1;
    int64_t idx1_pos, first_packet_pos = 0, data_offset = 0;

    nb_index_entries = size / 16;
    if (nb_index_entries <= 0)
        return -1;

    idx1_pos = avio_tell(pb);
    avio_seek(pb, avi->movi_list+4, SEEK_SET);
    if (avi_sync(s, 1) == 0) {
        first_packet_pos = avio_tell(pb) - 8;
    }
    avi->stream_index = -1;
    avio_seek(pb, idx1_pos, SEEK_SET);

    /* Read the entries and sort them in each stream component. */
    for(i = 0; i < nb_index_entries; i++) {
        tag = avio_rl32(pb);
        flags = avio_rl32(pb);
        pos = avio_rl32(pb);
        len = avio_rl32(pb);
        av_dlog(s, "%d: tag=0x%x flags=0x%x pos=0x%x len=%d/",
                i, tag, flags, pos, len);

        index = ((tag & 0xff) - '0') * 10;
        index += ((tag >> 8) & 0xff) - '0';
        if (index >= s->nb_streams)
            continue;
        st = s->streams[index];
        ast = st->priv_data;

        if(first_packet && first_packet_pos && len) {
            data_offset = first_packet_pos - pos;
            first_packet = 0;
        }
        pos += data_offset;

        av_dlog(s, "%d cum_len=%"PRId64"\n", len, ast->cum_len);

        if(url_feof(pb))
            return -1;

        if(last_pos == pos)
            avi->non_interleaved= 1;
        else if(len || !ast->sample_size)
            av_add_index_entry(st, pos, ast->cum_len, len, 0, (flags&AVIIF_INDEX) ? AVINDEX_KEYFRAME : 0);
        ast->cum_len += get_duration(ast, len);
        last_pos= pos;
    }
    return 0;
}