Swift AVFoundation stitching multiple videos together and keep preferred transform - ios

Question

I'm trying to stitch multiple video clips together. If I stitch each AVAsset in one AVMutableCompositionTrack it works but loses the transformation on the first asset by appending another one with enabled mirroring mode for front facing camera. Can I somehow use multiple AVMutableCompositionTrack of type video in one AVMutableComposition?
// create mix composition
let mixComposition = AVMutableComposition()
// insert video track
let videoCompositionTrack = mixComposition.addMutableTrack(withMediaType: AVMediaType.video, preferredTrackID: kCMPersistentTrackID_Invalid)
// keep track of total duration
var totalDuration = kCMTimeZero
// for each video clip add to mutable composition and transform each video layer
for (index, videoClip) in videoClips.enumerated() {
if let videoAsset = videoClip.asset, let videoAssetTrack = videoAsset.tracks(withMediaType: AVMediaType.video).first {
// insert current video track to composition
try videoCompositionTrack!.insertTimeRange(CMTimeRangeMake(kCMTimeZero, videoAsset.duration), of: videoAssetTrack, at: totalDuration)
videoCompositionTrack?.preferredTransform = videoAssetTrack.preferredTransform
// shift duration to next
totalDuration = CMTimeAdd(totalDuration, videoAsset.duration)
}
}
// Use AVAssetExportSession to export video
let assetExport = AVAssetExportSession(asset: mixComposition, presetName: AVAssetExportPreset1920x1080)
assetExport?.outputFileType = AVFileType.mp4
// get needed save url to save the video to recommended url
let movieDestinationUrl = self.getRecommendedSaveUrl()
// seting up asset export session
assetExport?.outputURL = movieDestinationUrl
assetExport?.shouldOptimizeForNetworkUse = true
// export video to file system asyc
assetExport?.exportAsynchronously(completionHandler: {
assetExport?.cancelExport()
switch assetExport!.status {
case AVAssetExportSessionStatus.failed:
break
case AVAssetExportSessionStatus.cancelled:
break
default:
DispatchQueue.main.async {
completion?(movieDestinationUrl, nil)
}
}
if ((assetExport?.error) != nil) {
AppDelegate.logger.error("Could not create user video: \((assetExport?.error)!)")
DispatchQueue.main.async {
completion?(nil, assetExport?.error)
}
}
})
I'm trying to use something like this and multiple AVMutableCompositionTrack's with different CGAffineTransform objects.
// create mix composition
let mixComposition = AVMutableComposition()
// keep track of total duration
var totalDuration = kCMTimeZero
// for each video clip add to mutable composition and transform each video layer
for (index, videoClip) in videoClips.enumerated() {
if let videoAsset = videoClip.asset, let videoAssetTrack = videoAsset.tracks(withMediaType: AVMediaType.video).first {
// insert video track
let videoCompositionTrack = mixComposition.addMutableTrack(withMediaType: AVMediaType.video, preferredTrackID: CMPersistentTrackID(index))
// insert current video track to composition
try videoCompositionTrack!.insertTimeRange(CMTimeRangeMake(kCMTimeZero, videoAsset.duration), of: videoAssetTrack, at: totalDuration)
videoCompositionTrack?.preferredTransform = videoAssetTrack.preferredTransform
// shift duration to next
totalDuration = CMTimeAdd(totalDuration, videoAsset.duration)
}
}
// Use AVAssetExportSession to export video
let assetExport = AVAssetExportSession(asset: mixComposition, presetName: AVAssetExportPreset1920x1080)
assetExport?.outputFileType = AVFileType.mp4
// get needed save url to save the video to recommended url
let movieDestinationUrl = self.getRecommendedSaveUrl()
// seting up asset export session
assetExport?.outputURL = movieDestinationUrl
assetExport?.shouldOptimizeForNetworkUse = true
// export video to file system asyc
assetExport?.exportAsynchronously(completionHandler: {
assetExport?.cancelExport()
switch assetExport!.status {
case AVAssetExportSessionStatus.failed:
break
case AVAssetExportSessionStatus.cancelled:
break
default:
DispatchQueue.main.async {
completion?(movieDestinationUrl, nil)
}
}
if ((assetExport?.error) != nil) {
AppDelegate.logger.error("Could not create user video: \((assetExport?.error)!)")
DispatchQueue.main.async {
completion?(nil, assetExport?.error)
}
}
})
In the case above I'm not able to get any useable video: it is much shorter than it should be. I'm trying to avoid using any AVMutableVideoCompositionInstruction because it takes too long to process but it would still be an option if it worked for any resolution and especially with mirroring support.
// create mix composition
let mixComposition = AVMutableComposition()
// keep track of total duration
var totalDuration = kCMTimeZero
// keeps all layer transformations for each video asset
var videoCompositionLayerInstructions = [AVMutableVideoCompositionLayerInstruction]()
// for each video clip add to mutable composition and transform each video layer
for (index, videoClip) in videoClips.enumerated() {
if let videoAsset = videoClip.asset {
// use first video asset track for setting like height and width
let videoAssetTrack = videoAsset.tracks(withMediaType: AVMediaType.video).first!
// insert video trakc
let videoCompositionTrack = mixComposition.addMutableTrack(withMediaType: AVMediaType.video, preferredTrackID: CMPersistentTrackID(index))
// insert current video track to composition
try videoCompositionTrack!.insertTimeRange(CMTimeRangeMake(totalDuration, videoAssetTrack.timeRange.duration), of: videoAssetTrack, at: totalDuration)
videoCompositionTrack?.preferredTransform = videoAssetTrack.preferredTransform
let videoCompositionLayerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: videoAssetTrack)
videoCompositionLayerInstruction.setTransform((videoCompositionTrack?.preferredTransform)!, at: totalDuration)
videoCompositionLayerInstruction.setOpacity(0.0, at: videoAsset.duration)
// apply instruction
videoCompositionLayerInstructions.append(videoCompositionLayerInstruction)
// shift duration to next
totalDuration = CMTimeAdd(totalDuration, videoAsset.duration)
}
}
let videoCompositionInstruction = AVMutableVideoCompositionInstruction()
videoCompositionInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, totalDuration)
videoCompositionInstruction.layerInstructions = videoCompositionLayerInstructions
let mainComposition = AVMutableVideoComposition()
mainComposition.renderSize = CGSize(width: 1080, height: 1920)
mainComposition.frameDuration = CMTimeMake(1, 30)
mainComposition.instructions = [videoCompositionInstruction]
// Use AVAssetExportSession to export video
let assetExport = AVAssetExportSession(asset: mixComposition, presetName: AVAssetExportPreset1920x1080)
assetExport?.outputFileType = AVFileType.mp4
// get needed save url to save the video to recommended url
let movieDestinationUrl = self.getRecommendedSaveUrl()
// seting up asset export session
assetExport?.outputURL = movieDestinationUrl
assetExport?.shouldOptimizeForNetworkUse = true
assetExport?.videoComposition = mainComposition
Anybody an idea how to implement this functionality?
Note: I don't need to care about audio at all.