`AVMutableCompositionTrack.insertTimeRange` fails with error -11800

Question

I'm creating AVMutableComposition from video and audio tracks:

func makeComposition(videoTrack: AVAssetTrack, audioTrack: AVAssetTrack) -> AVComposition {
    let composition = AVMutableComposition()
    /* ... */
    let compositionAudioTrack = composition.addMutableTrack(withMediaType: .audio)!
    try compositionAudioTrack.insertTimeRange(someRange, of: audioTrack, at: .zero) // Error!
    /* ... */
    return composition
}

and insertTimeRange(_:of:at:) fails with AVFoundationError -11800 AVError.code.unknown and undocumented underlying NSOSStatusError -12780. What might be the case?

Answer 1

Turns out, by the time I call insertTimeRange the source AVAsset of audioTrack got released. AVAssetTrack keeps weak reference to source AVAsset, so you must retain AVAsset in order to use AVAssetTrack.