Why is the only available AVAssetExportSession.outputFileType = AVFileTypeQuickTimeMovie

Question

I've set up an AVAssetExportSession with just 2 tracks of audio and no video, which plays just like I want it to in the AVPlayer - but as I go to export it, the only available outputFileType is AVFileTypeQuickTimeMovie - Why can't I choose an audio format?

When I NSLog(@"%@", [session supportedFileTypes]); i get;

[51330:c07] (
    "com.apple.quicktime-movie"
)

Here is my code;

- (AVMutableComposition *)getComposition {
    AVAsset *backingAsset = [AVAsset assetWithURL:self.urlForEightBarAudioFile];
    AVAsset *vocalsAsset = [AVAsset assetWithURL:self.recorder.url];
    AVMutableComposition *composition = [AVMutableComposition composition];
    AVMutableCompositionTrack *compositionBackingTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
    AVMutableCompositionTrack *compositionVocalTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

    AVAssetTrack *backingAssetTrack = [backingAsset.tracks objectAtIndex:0];
    AVAssetTrack *vocalsAssetTrack = [vocalsAsset.tracks objectAtIndex:0];

    CMTimeRange timeRange = CMTimeRangeFromTimeToTime(kCMTimeZero, backingAsset.duration);

    [compositionBackingTrack insertTimeRange:timeRange ofTrack:backingAssetTrack atTime:kCMTimeZero error:nil];
    [compositionVocalTrack insertTimeRange:timeRange ofTrack:vocalsAssetTrack atTime:kCMTimeZero error:nil];

    return composition;
}


- (IBAction)acceptRecording:(id)sender {
    AVAssetExportSession * session = [[AVAssetExportSession alloc] initWithAsset:[self getComposition] presetName:AVAssetExportPresetMediumQuality];
    NSURL *output = [self.urlForPathToEightBarRecordings URLByAppendingPathComponent:@"mix.mov"];
    session.outputURL = output;
    session.outputFileType = AVFileTypeQuickTimeMovie;

    NSLog(@"%@", [session supportedFileTypes]);
    [session exportAsynchronouslyWithCompletionHandler:^() {
        switch (session.status) {
            case AVAssetExportSessionStatusCompleted:
                NSLog(@"It's done...hallelujah");
                break;

            default:
                break;
        }
    }];
}

Answer 1

Ah right so the reason why it was only giving me the option of quicktime movie was because my preset was set to AVAssetExportPresetMediumQuality which is a video only preset I guess. I set my preset to AVAssetExportPresetAppleM4A and the output file type to AVFileTypeAppleM4A and export was a success!

Answer 2

You can use these settings for 128kbps

Preset time: AVAssetExportPresetMediumQuality

OutputfileType AVFileTypeMPEG

format: mp4