static int mxf_read_cryptographic_context(void *arg, AVIOContext *pb, int tag, int size, UID uid, int64_t klv_offset)
{
    MXFCryptoContext *cryptocontext = arg;
    if (size != 16)
        return AVERROR_INVALIDDATA;
    if (IS_KLV_KEY(uid, mxf_crypto_source_container_ul))
        avio_read(pb, cryptocontext->source_container_ul, 16);
    return 0;
}
static int mxf_read_cryptographic_context(void *arg, AVIOContext *pb, int tag, int size, UID uid, int64_t klv_offset)
{
    MXFCryptoContext *cryptocontext = arg;
    if (size != 16)
        return AVERROR_INVALIDDATA;
    if (IS_KLV_KEY(uid, mxf_crypto_source_container_ul))
        avio_read(pb, cryptocontext->source_container_ul, 16);
    return 0;
}