MP4GetSampleRenderingOffset - Get the rendering offset of a track
hFile Specifies the mp4 file to which the operation applies.
Specifies the track to which the operation applies.
Specifies the sample to which the operation applies. Caveat: the
first sample has id 1 not 0.
Upon success, the rendering offset in track time scale units. Upon an
MP4GetSampleRenderingOffset returns the rendering offset of the
specified sample from the specified track in the track time scale
units. See MP4ConvertFromTrackDuration() for how to map this value to
another time scale.
The sample rendering offset is typically zero for all media types other
than video. For video, encodings such as those defined by MPEG have
three types of frames: I, P, and B. To increase coding efficiency B
frames can depend on I or P frames that should be rendered after the B
frame. However to decode the B frame the I or P frame must already have
been decoded. This situation is addressed by placing the frames in
decoding order in the video track, and then setting the rendering
offset property to indicate when the video frame should actually be
rendered to the screen. Hence the start time of a sample indicates when
it should be decoded, the start time plus the rendering offset
indicates when it should be rendered.