AVAssetExportSession export takes a lot of time - ios

Question

My goal is to let user select video from photos and then let him to add labels over it.
Here is what I've got:
let audioAsset = AVURLAsset(url: selectedVideoURL)
let videoAsset = AVURLAsset(url: selectedVideoURL)
let mixComposition = AVMutableComposition()
let compositionVideoTrack = mixComposition.addMutableTrack(withMediaType: AVMediaTypeVideo, preferredTrackID: Int32(kCMPersistentTrackID_Invalid))
let compositionAudioTrack = mixComposition.addMutableTrack(withMediaType: AVMediaTypeAudio, preferredTrackID: Int32(kCMPersistentTrackID_Invalid))
let clipVideoTrack = videoAsset.tracks(withMediaType: AVMediaTypeVideo)[0]
let clipAudioTrack = audioAsset.tracks(withMediaType: AVMediaTypeAudio)[0]
do {
try compositionVideoTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero, videoAsset.duration), of: clipVideoTrack, at: kCMTimeZero)
try compositionAudioTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero, audioAsset.duration), of: clipAudioTrack, at: kCMTimeZero)
compositionVideoTrack.preferredTransform = clipVideoTrack.preferredTransform
} catch {
print(error)
}
var videoSize = clipVideoTrack.naturalSize
if isVideoPortrait(asset: videoAsset) {
videoSize = CGSize(width: videoSize.height, height: videoSize.width)
}
let parentLayer = CALayer()
let videoLayer = CALayer()
parentLayer.frame = CGRect(x: 0, y: 0, width: videoSize.width, height: videoSize.height)
videoLayer.frame = CGRect(x: 0, y: 0, width: videoSize.width, height: videoSize.height)
parentLayer.addSublayer(videoLayer)
// adding label
let helloLabelLayer = CATextLayer()
helloLabelLayer.string = "Hello"
helloLabelLayer.font = "Signika-Semibold" as CFTypeRef?
helloLabelLayer.fontSize = 30.0
helloLabelLayer.contentsScale = mainScreen.scale
helloLabelLayer.alignmentMode = kCAAlignmentNatural
helloLabelLayer.frame = CGRect(x: 0.0, y: 0.0, width: 100.0, height: 50.0)
parentLayer.addSublayer(helloLabelLayer)
// creating composition
let videoComp = AVMutableVideoComposition()
videoComp.renderSize = videoSize
videoComp.frameDuration = CMTimeMake(1, 30)
videoComp.animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayer: videoLayer, in: parentLayer)
let instruction = AVMutableVideoCompositionInstruction()
instruction.timeRange = CMTimeRangeMake(kCMTimeZero, mixComposition.duration)
let layerInstruction = videoCompositionInstructionForTrack(track: compositionVideoTrack, asset: videoAsset)
instruction.layerInstructions = [layerInstruction]
videoComp.instructions = [instruction]
if let assetExport = AVAssetExportSession(asset: mixComposition, presetName: AVAssetExportPreset640x480) {
let filename = NSTemporaryDirectory().appending("video.mov")
if FileManager.default.fileExists(atPath: filename) {
do {
try FileManager.default.removeItem(atPath: filename)
} catch {
print(error)
}
}
let url = URL(fileURLWithPath: filename)
assetExport.outputURL = url
assetExport.outputFileType = AVFileTypeMPEG4
assetExport.videoComposition = videoComp
print(NSDate().timeIntervalSince1970)
assetExport.exportAsynchronously {
print(NSDate().timeIntervalSince1970)
let library = ALAssetsLibrary()
library.writeVideoAtPath(toSavedPhotosAlbum: url, completionBlock: {
(url, error) in
switch assetExport.status {
case AVAssetExportSessionStatus.failed:
p("failed \(assetExport.error)")
case AVAssetExportSessionStatus.cancelled:
p("cancelled \(assetExport.error)")
default:
p("complete")
p(NSDate().timeIntervalSince1970)
if FileManager.default.fileExists(atPath: filename) {
do {
try FileManager.default.removeItem(atPath: filename)
} catch {
p(error)
}
}
print("Exported")
}
})
}
Implementation of isVideoPortrait function:
func isVideoPortrait(asset: AVAsset) -> Bool {
var isPortrait = false
let tracks = asset.tracks(withMediaType: AVMediaTypeVideo)
if tracks.count > 0 {
let videoTrack = tracks[0]
let t = videoTrack.preferredTransform
if t.a == 0 && t.b == 1.0 && t.c == -1.0 && t.d == 0 {
isPortrait = true
}
if t.a == 0 && t.b == -1.0 && t.c == 1.0 && t.d == 0 {
isPortrait = true
}
if t.a == 1.0 && t.b == 0 && t.c == 0 && t.d == 1.0 {
isPortrait = false
}
if t.a == -1.0 && t.b == 0 && t.c == 0 && t.d == -1.0 {
isPortrait = false
}
}
return isPortrait
}
And the last function for video composition layer instruction:
func videoCompositionInstructionForTrack(track: AVCompositionTrack, asset: AVAsset) -> AVMutableVideoCompositionLayerInstruction {
let instruction = AVMutableVideoCompositionLayerInstruction(assetTrack: track)
let assetTrack = asset.tracks(withMediaType: AVMediaTypeVideo)[0]
let transform = assetTrack.preferredTransform
instruction.setTransform(transform, at: kCMTimeZero)
return instruction
}
The code works well, output video has label, but if I select 1 minute video, export takes 28 seconds.
I've search for it and tried to remove layerInsctuction transform, but no effect.
Tried to add:
assetExport.shouldOptimizeForNetworkUse = false
no effect either.
Also, tried to set AVAssetExportPresetPassthrough for AVAssetExportSession, in this case video exports with 1 second but labels have gone.
Any help would be appreciated, because I'm in stuck. Thanks for your time.

Answer 1

The only way I can think of is to reduce the quality via the bit rate and resolution.
This is done through a dictionary applied to the videoSettings of the AssetExporter, for this to work I had to use a Framework called SDAVAssetExportSession
Then by changing the videoSettings I could play with the quality to get an optimal quality / speed.
let compression = [AVVideoAverageBitRateKey : 2097152(DESIRED_BITRATE),AVVideoProfileLevelKey : AVVideoProfileLevelH264BaselineAutoLevel]
let videoSettings = [AVVideoCodecKey : AVVideoCodecH264, AVVideoWidthKey : maxWidth, AVVideoHeightKey : maxHeight, AVVideoCompressionPropertiesKey:compression]
This was the only way I could speed things up.

Answer 2

This is not directly relevant to your question, but your code here is backwards:
assetExport.exportAsynchronously {
let library = ALAssetsLibrary()
library.writeVideoAtPath(toSavedPhotosAlbum: url, completionBlock: {
switch assetExport.status {
No no no. First you complete the asset export. Then you can copy again to somewhere else if that's what you want to do. So this needs to go like this:
assetExport.exportAsynchronously {
switch assetExport.status {
case .completed:
let library = ALAssetsLibrary()
library.writeVideoAtPath...
Other comments:
ALAssetsLibrary is dead. This is not the way to copy into the user's photo library. Use Photo framework.
Your original code is very odd, because there are a lot of other cases you are not testing for. You are just assuming that default means .completed. That's dangerous.