问题
When I overlay an image on my video, the video quality is greatly reduced. If I don't set the video composition of the export session or set the export quality to passthrough, the video quality is great (but I get no overlays obviously).
I'm passing in a local .mov video url to add the overlays too. I'm using PHPhotoLibrary to save the video to the camera roll. Using some other functions to transform the video and set its instructions.
It all seems pretty straightforward, but something is killing the video quality
func merge3(url: URL) {
let firstAsset = AVAsset(url: url)
// 1 - Create AVMutableComposition object. This object will hold your AVMutableCompositionTrack instances.
let mixComposition = AVMutableComposition()
// 2 - Create two video tracks
guard
let firstTrack = mixComposition.addMutableTrack(withMediaType: AVMediaType.video,
preferredTrackID: Int32(kCMPersistentTrackID_Invalid))
else {
return
}
do {
try firstTrack.insertTimeRange(CMTimeRangeMake(start: CMTime.zero, duration: firstAsset.duration),
of: firstAsset.tracks(withMediaType: AVMediaType.video)[0],
at: CMTime.zero)
} catch {
print("Failed to load first track")
return
}
let s = UIScreen.main.bounds
let imglogo = UIImage(named: "django")?.scaleImageToSize(newSize: CGSize(width: 250, height: 125))
let imglayer = CALayer()
imglayer.contents = imglogo?.cgImage
imglayer.frame = CGRect(x: s.width / 2 - 125, y: s.height / 2 - 67.5
, width: 250, height: 125)
imglayer.opacity = 1.0
let videolayer = CALayer()
videolayer.frame = CGRect(x: 0, y: 0, width: s.width, height: s.height)
let parentlayer = CALayer()
parentlayer.frame = CGRect(x: 0, y: 0, width: s.width, height: s.height)
parentlayer.addSublayer(videolayer)
parentlayer.addSublayer(imglayer)
// 2.1
let mainInstruction = AVMutableVideoCompositionInstruction()
mainInstruction.timeRange = CMTimeRangeMake(start: CMTime.zero,
duration: firstAsset.duration)
let layercomposition = AVMutableVideoComposition()
layercomposition.frameDuration = CMTimeMake(value: 1, timescale: 30)
layercomposition.animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayer: videolayer, in: parentlayer)
layercomposition.renderSize = CGSize(width: UIScreen.main.bounds.width, height: UIScreen.main.bounds.height)
// instruction for watermark
let instruction = AVMutableVideoCompositionInstruction()
instruction.timeRange = CMTimeRangeMake(start: CMTime.zero, duration: firstAsset.duration)
_ = mixComposition.tracks(withMediaType: AVMediaType.video)[0] as AVAssetTrack
let layerinstruction = VideoHelper.videoCompositionInstruction1(firstTrack, asset: firstAsset)
instruction.layerInstructions = [layerinstruction]
layercomposition.instructions = [instruction]
// 4 - Get path
guard let documentDirectory = FileManager.default.urls(for: .documentDirectory,
in: .userDomainMask).first else {
return
}
let dateFormatter = DateFormatter()
dateFormatter.dateStyle = .long
dateFormatter.timeStyle = .short
let date = dateFormatter.string(from: Date())
let url = documentDirectory.appendingPathComponent("mergeVideo-\(date).mov")
// 5 - Create Exporter
guard let exporter = AVAssetExportSession(asset: mixComposition,
presetName: AVAssetExportPresetHighestQuality) else {
return
}
exporter.outputURL = url
exporter.outputFileType = AVFileType.mov
exporter.shouldOptimizeForNetworkUse = true
exporter.videoComposition = layercomposition
// 6 - Perform the Export
exporter.exportAsynchronously() {
DispatchQueue.main.async {
self.exportDidFinish(exporter)
}
}
}
func exportDidFinish(_ session: AVAssetExportSession) {
guard
session.status == AVAssetExportSession.Status.completed,
let outputURL = session.outputURL
else {
return
}
let saveVideoToPhotos = {
PHPhotoLibrary.shared().performChanges({
PHAssetChangeRequest.creationRequestForAssetFromVideo(atFileURL: outputURL)
}) { saved, error in
let success = saved && (error == nil)
let title = success ? "Success" : "Error"
let message = success ? "Video saved" : "Failed to save video"
let alert = UIAlertController(title: title, message: message, preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "OK", style: UIAlertAction.Style.cancel, handler: nil))
self.present(alert, animated: true, completion: nil)
}
}
// Ensure permission to access Photo Library
if PHPhotoLibrary.authorizationStatus() != .authorized {
PHPhotoLibrary.requestAuthorization { status in
if status == .authorized {
saveVideoToPhotos()
}
}
} else {
saveVideoToPhotos()
}
}
static func videoCompositionInstruction1(_ track: AVCompositionTrack, asset: AVAsset)
-> AVMutableVideoCompositionLayerInstruction {
let instruction = AVMutableVideoCompositionLayerInstruction(assetTrack: track)
let assetTrack = asset.tracks(withMediaType: .video)[0]
let transform = assetTrack.preferredTransform
let assetInfo = orientationFromTransform(transform)
var scaleToFitRatio = UIScreen.main.bounds.width / assetTrack.naturalSize.width
if assetInfo.isPortrait { // not hit
scaleToFitRatio = UIScreen.main.bounds.width / assetTrack.naturalSize.height
let scaleFactor = CGAffineTransform(scaleX: scaleToFitRatio, y: scaleToFitRatio)
instruction.setTransform(assetTrack.preferredTransform.concatenating(scaleFactor), at: CMTime.zero)
} else { // hit
let scaleFactor = CGAffineTransform(scaleX: scaleToFitRatio, y: scaleToFitRatio)
var concat = assetTrack.preferredTransform.concatenating(scaleFactor)
.concatenating(CGAffineTransform(translationX: 0, y: UIScreen.main.bounds.width / 4))
if assetInfo.orientation == .down { // not hit
let fixUpsideDown = CGAffineTransform(rotationAngle: CGFloat(Double.pi))
let windowBounds = UIScreen.main.bounds
let yFix = assetTrack.naturalSize.height + windowBounds.height
let centerFix = CGAffineTransform(translationX: assetTrack.naturalSize.width, y: yFix)
concat = fixUpsideDown.concatenating(centerFix).concatenating(scaleFactor)
}
instruction.setTransform(concat, at: CMTime.zero)
}
return instruction
}
static func orientationFromTransform(_ transform: CGAffineTransform)
-> (orientation: UIImage.Orientation, isPortrait: Bool) {
var assetOrientation = UIImage.Orientation.up
var isPortrait = false
if transform.a == 0 && transform.b == 1.0 && transform.c == -1.0 && transform.d == 0 {
assetOrientation = .right
isPortrait = true
} else if transform.a == 0 && transform.b == -1.0 && transform.c == 1.0 && transform.d == 0 {
assetOrientation = .left
isPortrait = true
} else if transform.a == 1.0 && transform.b == 0 && transform.c == 0 && transform.d == 1.0 {
assetOrientation = .up
} else if transform.a == -1.0 && transform.b == 0 && transform.c == 0 && transform.d == -1.0 {
assetOrientation = .down
}
return (assetOrientation, isPortrait)
}
回答1:
You are setting your
layercomposition.renderSize = CGSize(width: UIScreen.main.bounds.width, height: UIScreen.main.bounds.height)
when it should be
layercomposition.renderSize = yourAsset.tracks(withMediaType: AVMediaTypeVideo)[0].naturalSize
What the first one does is set your resolution to your screen size and not the actual size of the original video. The 2nd one corrects it to setting the resolution of the original video.
Think of it this way - you don't want your resolution to be the size of your screen - that would be really small. You want it the size of some original video or the size of some commonly used video setting.
来源：https://stackoverflow.com/questions/57225191/overlaying-image-on-video-reduces-video-resolution