avcodec_flush_buffers(st->codec);
double secs = (double)pos / sample_rate;
int64_t tstmp = secs * st->time_base.den / st->time_base.num;
avcodec_flush_buffers(st->codec);
double secs = (double)pos / sample_rate;
int64_t tstmp = secs * st->time_base.den / st->time_base.num;