static int mov_read_extradata(MOVContext *c, AVIOContext *pb, MOVAtom atom)
{
    AVStream *st;
    uint64_t size;
    uint8_t *buf;
    int err;

    if (c->fc->nb_streams < 1) // will happen with jp2 files
        return 0;
    st= c->fc->streams[c->fc->nb_streams-1];
    size= (uint64_t)st->codec->extradata_size + atom.size + 8 + FF_INPUT_BUFFER_PADDING_SIZE;
    if (size > INT_MAX || (uint64_t)atom.size > INT_MAX)
        return AVERROR_INVALIDDATA;
    if ((err = av_reallocp(&st->codec->extradata, size)) < 0) {
        st->codec->extradata_size = 0;
        return err;
    }
    buf = st->codec->extradata + st->codec->extradata_size;
    st->codec->extradata_size= size - FF_INPUT_BUFFER_PADDING_SIZE;
    AV_WB32(       buf    , atom.size + 8);
    AV_WL32(       buf + 4, atom.type);

    err = ffio_read_size(pb, buf + 8, atom.size);
    if (err < 0)
        return err;

    return 0;
}