关于MP4 fileformat中 duration及timescale相关的几个地方

1 mvhd

Time scale

A time value that indicates the time scale for this movie—that is, the number of time units that

pass per second in its time coordinate system. A time coordinate system that measures time

in sixtieths of a second, for example, has a time scale of 60.

Duration

A time value that indicates the duration of the movie in time scale units. Note that this property

is derived from the movie’s tracks. The value of this field corresponds to the duration of the

longest track in the movie.

2 tkhd

Duration

A time value that indicates the duration of this track (in the movie’s time coordinate system).

Note that this property is derived from the track’s edits. The value of this field is equal to the

sum of the durations of all of the track’s edits. If there is no edit list, then the duration is the

sum of the sample durations, converted into the movie timescale.

3 mdhd

Time scale

A time value that indicates the time scale for this media—that is, the number of time units that

pass per second in its time coordinate system.

Duration

The duration of this media in units of its time scale.