AVAssetExportSession audio missing in iOS9 - audio

Question

I have a code to export a video file. The code works fine on iOS8, but on devices with iOS9 there is no sound on the video file.
I think the problem is on the AVAssetExportSession, but I'm unable to finde the issue and fix it.
What is also weird, is the asset works fine when I export it for playback.
(void)export {
self.videoComposition.renderScale = 1.0;
self.videoComposition.animationTool = [self coreAnimationTool];
FakeAsset * assetFaker = [FakeAsset new];
[assetFaker fakeAssetWithDuration:self.currentTime completitionBlock:^(AVAsset *asset) {
[self addEmptyBackgroundTrackFromAsset:asset];
AVAssetExportSession * exportSession =
[AVAssetExportSession exportSessionWithAsset:[self.composition copy]
presetName:AVAssetExportPresetHighestQuality];
[MovieExport setCurrentExporter:exportSession];
NSUInteger i = 0;
NSString * path;
do {
path =
[NSTemporaryDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:#"movieExport%i.mov",i]]; i++;
} while ([[NSFileManager defaultManager] fileExistsAtPath:path isDirectory:NULL]);
NSURL * url = [NSURL fileURLWithPath:path];
if ([[NSFileManager defaultManager] fileExistsAtPath:path]) {
[[NSFileManager defaultManager] removeItemAtURL:url error:nil];
}
exportSession.outputURL = url;
exportSession.outputFileType = AVFileTypeMPEG4;
exportSession.audioMix = self.audioMix;
exportSession.videoComposition = self.videoComposition;
exportSession.timeRange = CMTimeRangeMake(kCMTimeZero, self.currentTime);
[exportSession exportAsynchronouslyWithCompletionHandler:^{
switch (exportSession.status) {
case AVAssetExportSessionStatusCompleted:
self.callback(#{MovieCreatorVideoURL : exportSession.outputURL}, nil);
break;
case AVAssetExportSessionStatusFailed:
self.callback(nil,exportSession.error);
break;
case AVAssetExportSessionStatusCancelled:
self.callback(nil, exportSession.error);
break;
default:
break;
}
}];
}];
}
- (void)exportForPlayback {
self.videoComposition.renderScale = 2.0;
FakeAsset * assetFaker = [FakeAsset new];
[assetFaker fakeAssetWithDuration:self.currentTime completitionBlock:^(AVAsset *asset){
[self addEmptyBackgroundTrackFromAsset:asset];
AVPlayerItem * playerItem = [AVPlayerItem playerItemWithAsset:self.composition];
playerItem.videoComposition = self.videoComposition;
playerItem.audioMix = self.audioMix;
MovieMetadata * metaData = [MovieMetadata new];
metaData.orderedElements = self.orderedElements;
metaData.orderedMarkers = self.movieMarkers;
metaData.elementBeginTimes = self.elementBeginTimes;
metaData.filmSize = self.filmSize;
metaData.filmFormat = self.filmFormat;
metaData.filmQuality = self.filmQuality;
self.userInfos =
#{MovieCreatorAnimations : self.animationLayer,
MovieCreatorAVPlayerItem : playerItem,
MovieCreatorMetadata : metaData};
self.callback(self.userInfos, nil);
}];
}

Answer 1

I found the issue.
My AVMutableComposition have multiple AVMutableCompositionTrack. If one AVMutableCompositionTrack don't have a track, the video exported will be mute on iOS9 but will work correctly on iOS8
To fix this issue, when I initialize the AVMutableCompositionTrack, I add audio with no sound.
-(void)initEmptyAudio:(AVMutableCompositionTrack *) obj{
NSString* path = [[NSBundle mainBundle] pathForResource:#"emptyAudio" ofType:#"mp3"];
NSURL* audio_inputFileUrl = [NSURL fileURLWithPath:path];
AVURLAsset* audioAsset = [[AVURLAsset alloc]initWithURL:audio_inputFileUrl options:nil];
CMTimeRange audio_timeRange = CMTimeRangeMake(kCMTimeZero, audioAsset.duration);
[obj insertTimeRange:audio_timeRange ofTrack:[[audioAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:CMTimeMake(0,1) error:nil];
}