MP4GetTrackNumberOfSamples man page
MP4GetTrackNumberOfSamples — Get the number of samples in a track
Specifies the mp4 file to which the operation applies.
Specifies the track for which the number of samples is desired.
Upon success, the number of samples in the track. Upon an error, 0.
MP4GetTrackNumberOfSamples returns the number of samples in the specified track in the mp4 file. Sample id's are the consecutive sequence of numbers from 1 to the total number of samples, i.e. 1-based indexing, not 0-based indexing.