if (fabs(av_q2d(st->codec->time_base) - 1/25.0) < 0.0001) {
samples_per_frame = PAL_samples_per_frame;
mxf->time_base = (AVRational){ 1, 25 };
if (fabs(av_q2d(st->codec->time_base) - 1/25.0) < 0.0001) {
samples_per_frame = PAL_samples_per_frame;
mxf->time_base = (AVRational){ 1, 25 };