What is wrong with my swift VideoWriter code? - ios

Question

I want to generate a mpeg video from a few images (as frames).
After I finish writing the video file, I tried saving it to Photos, but iOS consider it incompatible:
let compatible = AVAsset(url: video_url).isCompatibleWithSavedPhotosAlbum
print("COMPATIBILITY", compatible) // false
And then I tried creating an AVPlayer to play the video, and the video fails to play. So the video file must be corrupt somehow.
I reviewed my code closely, but couldn't spot the problem. Please help.
Here is my code:
class VideoWriter {
var url:URL?
var assetWriter:AVAssetWriter?
init(url:URL) {
self.url = url
do {
try self.assetWriter = AVAssetWriter(url: self.url!, fileType: AVFileTypeMPEG4)
} catch {
print("Fail to create assetWriter")
}
}
func writeFrames(frames:[UIImage], finishedHandler:#escaping ()->Void) {
let settings:[String:Any] = [
AVVideoCodecKey: AVVideoCodecH264,
AVVideoWidthKey: 480, //CANVAS_SIZE * 4 / 3,
AVVideoHeightKey: 360 //CANVAS_SIZE
]
let assetWriterInput = AVAssetWriterInput(mediaType: AVMediaTypeVideo, outputSettings: settings)
self.assetWriter?.add(assetWriterInput)
let bufferAttributes:[String: Any] = [kCVPixelBufferPixelFormatTypeKey as String: Int(kCVPixelFormatType_32ARGB)]
let bufferAdapter = AVAssetWriterInputPixelBufferAdaptor(assetWriterInput: assetWriterInput, sourcePixelBufferAttributes: bufferAttributes)
let frameTime = CMTimeMake(1, 30)
self.assetWriter?.startWriting()
self.assetWriter?.startSession(atSourceTime: kCMTimeZero)
// write the frames here
let mediaInputQueue = DispatchQueue(label: "mediaInputQueue")
var i = 0
let frameNumber = frames.count
assetWriterInput.requestMediaDataWhenReady(on: mediaInputQueue){
while(true){
if(i >= frameNumber){
break
}
if (assetWriterInput.isReadyForMoreMediaData){
let image = frames[i]
print("writing frame ", i)
let pixelBuffer = self.newPixelBufferFrom(cgImage: image.cgImage!)
var time:CMTime
if i == 0 {
time = kCMTimeZero
} else {
let value = i - 1
let lastTime = CMTimeMake(Int64(value), frameTime.timescale)
time = CMTimeAdd(lastTime, frameTime)
}
bufferAdapter.append(pixelBuffer!, withPresentationTime: time)
i += 1
}
}
assetWriterInput.markAsFinished()
self.assetWriter?.finishWriting(completionHandler: {
Thread.sleep(forTimeInterval: 0.5)
DispatchQueue.main.sync {
print("Completed?", self.assetWriter?.status == AVAssetWriterStatus.completed)
finishedHandler()
}
})
}
}
func newPixelBufferFrom(cgImage:CGImage) -> CVPixelBuffer?{
let options:[String: Any] = [kCVPixelBufferCGImageCompatibilityKey as String: true, kCVPixelBufferCGBitmapContextCompatibilityKey as String: true]
var pxbuffer:CVPixelBuffer?
let frameWidth = 480 //CANVAS_SIZE
let frameHeight = 360 //CANVAS_SIZE
let status = CVPixelBufferCreate(kCFAllocatorDefault, frameWidth, frameHeight, kCVPixelFormatType_32ARGB, options as CFDictionary?, &pxbuffer)
// TODO: throw exception in case of error, don't use assert
assert(status == kCVReturnSuccess && pxbuffer != nil, "newPixelBuffer failed")
CVPixelBufferLockBaseAddress(pxbuffer!, CVPixelBufferLockFlags(rawValue: 0))
let pxdata = CVPixelBufferGetBaseAddress(pxbuffer!)
let rgbColorSpace = CGColorSpaceCreateDeviceRGB()
let context = CGContext(data: pxdata, width: frameWidth, height: frameHeight, bitsPerComponent: 8, bytesPerRow: CVPixelBufferGetBytesPerRow(pxbuffer!), space: rgbColorSpace, bitmapInfo: CGImageAlphaInfo.noneSkipFirst.rawValue)
// TODO: throw exception in case of error, don't use assert
assert(context != nil, "context is nil")
context!.concatenate(CGAffineTransform.identity)
context!.draw(cgImage, in: CGRect(x: 0, y: 0, width: cgImage.width, height: cgImage.height))
CVPixelBufferUnlockBaseAddress(pxbuffer!, CVPixelBufferLockFlags(rawValue: 0))
return pxbuffer
}
}
btw. I didn't add audio input, is that necessary for a MPEG file?