Looping an iOS/OSX AudioToolbox MusicTrack in Swift

Loop.swift

    func loopTrack(musicTrack:MusicTrack)   {

        var trackLength = getTrackLength(musicTrack)
        println("track length is \(trackLength)")
        setTrackLoopDuration(musicTrack, duration: trackLength)
    }
    
    func getTrackLength(musicTrack:MusicTrack) -> MusicTimeStamp {
        
        //The time of the last music event in a music track, plus time required for note fade-outs and so on.
        var trackLength:MusicTimeStamp = 0
        var tracklengthSize:UInt32 = 0
        var status = MusicTrackGetProperty(musicTrack,
            UInt32(kSequenceTrackProperty_TrackLength),
            &trackLength,
            &tracklengthSize)
        if status != OSStatus(noErr) {
            println("Error getting track length \(status)")
            CheckError(status)
            return 0
        }
        println("track length is \(trackLength)")
        return trackLength
    }
    
    
    /*
The default looping behaviour is off (track plays once)
Looping is set by specifying the length of the loop. It loops from
(TrackLength - loop length) to Track Length
If numLoops is set to zero, it will loop forever.
To turn looping off, you set this with loop length equal to zero.
*/

    func setTrackLoopDuration(musicTrack:MusicTrack, duration:MusicTimeStamp)   {
        println("loop duration to \(duration)")
        
        //To loop forever, set numberOfLoops to 0. To explicitly turn off looping, specify a loopDuration of 0.
        var loopInfo = MusicTrackLoopInfo(loopDuration: duration, numberOfLoops: 0)
        var lisize:UInt32 = 0
        var status = MusicTrackSetProperty(musicTrack, UInt32(kSequenceTrackProperty_LoopInfo), &loopInfo, lisize )
        if status != OSStatus(noErr) {
            println("Error setting loopinfo on track \(status)")
            CheckError(status)
            return
        }
    }
    
    // or if you have a sequence as an ivar, you can do something like this
     func setTrackLoopDuration(duration:Float)   {
        var track:MusicTrack = nil
        var status = MusicSequenceGetIndTrack(self.musicSequence, 0, &track)
        CheckError(status)
        setTrackLoopDuration(track, duration: MusicTimeStamp(duration))
    }