I have created an avmutablecomposition and tried to use insertEmptyTimeRange to generate 1 minute of silence. This doesn't appear to be working. I have also tried creating an avmutablecompositiontrack using addMutableTrackWithMediaType:preferredTrackID: and then insertEmptyTimeRange on the track and still no success. To give some background on my app, I allow users to add audio samples a timeline and then playback or export and this is working really well using the av classes. The problem is that I need to make sure that the audio is exactly 1 min (for example). Regardless of the info about my specific app above, is it possible to insert an empty time range into a comp or comptrack?