if let Some(ref mut stream) = track.stream {
let tb_den = stream.tb_den;
let (tb_num, tb_den) = reduce_timebase(tb_num * stream.tb_num, tb_den);
if let Some(ref mut stream) = track.stream {
let tb_den = stream.tb_den;
let (tb_num, tb_den) = reduce_timebase(tb_num * stream.tb_num, tb_den);