Exporting Multiple Tracks: AVMutableComposition and AVAssetExportSession - ios

Question

I have 4 videos files which I have edited and added to a mutable composition. I am trying to use the export session to export the files, however, when I am exporting, only the first track in the list of tracks below gets exported
<AVAssetExportSession: 0x60800001da50, asset = <AVMutableComposition: 0x6080002240a0 tracks = (
"<AVMutableCompositionTrack: 0x600000224ca0 trackID = 1, mediaType = vide, editCount = 8>",
"<AVMutableCompositionTrack: 0x600000226da0 trackID = 2, mediaType = vide, editCount = 10>",
"<AVMutableCompositionTrack: 0x60000023e180 trackID = 3, mediaType = vide, editCount = 3>",
"<AVMutableCompositionTrack: 0x60000023e500 trackID = 4, mediaType = vide, editCount = 7>"
)>, presetName = AVAssetExportPreset1280x720, outputFileType = (null)
Only the first track with trackID = 1 gets exported. Here is the export session source:
// Create path to output file
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *myPathDocs = [documentsDirectory stringByAppendingPathComponent:
[NSString stringWithFormat:#"ProcessedVideo-%d.mov", arc4random() % 1000]];
NSURL *url = [NSURL fileURLWithPath:myPathDocs];
AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:batchComposition presetName:AVAssetExportPreset1280x720];
NSLog(#"%#", exporter);
exporter.outputURL = url;
exporter.outputFileType = AVFileTypeQuickTimeMovie;
[exporter exportAsynchronouslyWithCompletionHandler:^(void) {
switch (exporter.status) {
case AVAssetExportSessionStatusCompleted:
NSLog(#"Completed");
break;
case AVAssetExportSessionStatusFailed:
NSLog(#"Failed:%#",exporter.error);
break;
case AVAssetExportSessionStatusCancelled:
NSLog(#"Canceled:%#",exporter.error);
break;
default:
break;
}
}];
Does anyone have any ideas how I can get all 4 tracks to export to a single .mov file using export session?

Answer 1

You can only export to one NSURL with AVAssetExportSession. If you want to export 4 separate files, you will have to export 4 times.

Answer 2

Thanks to jlw for his help. What I found the problem was that I was adding multiple video tracks to mutable composition. What instead I should have done is made a single video track and applied all edits from the other asset tracks onto the single video tracks. Seems AVAssetExportSession will only export a single track as noted by jlw.
Summary:
Create mutable composition
Create mutable composition track
Apply asset tracks to the composition (insertTimeRange)
Export the mutable composition

Answer 3

I think there is no need to create new AVMutableComposition. Instead just assign your AVVideoComposition? to the videoComposition property of your exporter.
guard let playerItem = getPlayerItem() as? AVPlayerItem else {
return
}
let asset = playerItem.asset
let videoComposition: AVVideoComposition? = playerItem.videoComposition
let path = NSTemporaryDirectory().stringByAppendingFormat("/video.mov")
if NSFileManager.defaultManager().fileExistsAtPath(path) {
do {
try NSFileManager.defaultManager().removeItemAtPath(path)
} catch {
print("Temporary file removing error.")
}
}
let outputURL = NSURL.fileURLWithPath(path)
guard let exporter = AVAssetExportSession(asset: asset,
presetName: AVAssetExportPresetHighestQuality) else {
return
}
exporter.outputURL = outputURL
exporter.outputFileType = AVFileTypeQuickTimeMovie
exporter.shouldOptimizeForNetworkUse = true
exporter.videoComposition = videoComposition // 👈
exporter.exportAsynchronouslyWithCompletionHandler {
PHPhotoLibrary.sharedPhotoLibrary().performChanges({
PHAssetChangeRequest.creationRequestForAssetFromVideoAtFileURL(outputURL)
}) { (success: Bool, error: NSError?) -> Void in
if success {
} else {
}
}
}