An audio file can only play sound between two PCM samples (the 'start'
and 'end' of section of a wave form). Therefore when calculating
duration from a count of PCM samples we need to subtract one first (the
'end' sample which has no duration of its own).
This only changes durations by one PCM sample (21us - 22us for 44.1kHz sample
rate).
PiperOrigin-RevId: 596990306