Recording gapless audio with AVAssetWriter

Question

I\'m trying to record segments of audio and recombine them without producing a gap in audio.

The eventual goal is to also have video, but I\'ve found that audio itself c

Answer 1

Not sure if this helps you but if you have a bunch of MP4s you can use this code to combine them:

func mergeAudioFiles(audioFileUrls: NSArray, callback: (url: NSURL?, error: NSError?)->()) {

    // Create the audio composition
    let composition = AVMutableComposition()

    // Merge
    for (var i = 0; i < audioFileUrls.count; i++) {

        let compositionAudioTrack :AVMutableCompositionTrack = composition.addMutableTrackWithMediaType(AVMediaTypeAudio, preferredTrackID: CMPersistentTrackID())

        let asset = AVURLAsset(URL: audioFileUrls[i] as! NSURL)

        let track = asset.tracksWithMediaType(AVMediaTypeAudio)[0]

        let timeRange = CMTimeRange(start: CMTimeMake(0, 600), duration: track.timeRange.duration)

        try! compositionAudioTrack.insertTimeRange(timeRange, ofTrack: track, atTime: composition.duration)
    }

    // Create output url
    let format = NSDateFormatter()
    format.dateFormat="yyyy-MM-dd-HH-mm-ss"
    let currentFileName = "recording-\(format.stringFromDate(NSDate()))-merge.m4a"
    print(currentFileName)

    let documentsDirectory = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)[0]
    let outputUrl = documentsDirectory.URLByAppendingPathComponent(currentFileName)
    print(outputUrl.absoluteString)

    // Export it
    let assetExport = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetAppleM4A)
    assetExport?.outputFileType = AVFileTypeAppleM4A
    assetExport?.outputURL = outputUrl

    assetExport?.exportAsynchronouslyWithCompletionHandler({ () -> Void in
        switch assetExport!.status {
            case AVAssetExportSessionStatus.Failed:
                callback(url: nil, error: assetExport?.error)
            default:
                callback(url: assetExport?.outputURL, error: nil)
        }
    })

}