static int aax_filter(uint8_t *input, int size, MOVContext *c)
{
    int blocks = 0;
    unsigned char iv[16];

    memcpy(iv, c->file_iv, 16); // iv is overwritten
    blocks = size >> 4; // trailing bytes are not encrypted!
    av_aes_init(c->aes_decrypt, c->file_key, 128, 1);
    av_aes_crypt(c->aes_decrypt, input, input, blocks, iv, 1);

    return 0;
}