Difficulty Writing Pixel Buffer To Asset Writer on Certain Devices - ios

Question

I am working on a function in my app to write images from my sample buffer to an AVAssetWriter. Curiously, this works fine on a 10.5" iPad Pro, but causes a crash on a 7.9" iPad Mini 2. I can't fathom how the same code could be problematic on two different devices. But here's my code;
func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
// Setup the pixel buffer image
let pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)!
// Setup the format description
let formatDescription = CMSampleBufferGetFormatDescription(sampleBuffer)!
// Setup the current video dimensions
self.currentVideoDimensions = CMVideoFormatDescriptionGetDimensions(formatDescription)
// Setup the current sample time
self.currentSampleTime = CMSampleBufferGetOutputPresentationTimeStamp(sampleBuffer)
// Handle record
if self.isCapturing {
// Setup auto release pool
autoreleasepool {
// Setup the output image
let outputImage = CIImage(cvPixelBuffer: pixelBuffer)
// Ensure the video writer is ready for more data
if self.videoWriter?.assetWriterPixelBufferInput?.assetWriterInput.isReadyForMoreMediaData == true {
// Setup the new pixel buffer (THIS IS WHERE THE ERROR OCCURS)
var newPixelBuffer: CVPixelBuffer? = nil
// Setup the pixel buffer pool
CVPixelBufferPoolCreatePixelBuffer(nil, (self.videoWriter?.assetWriterPixelBufferInput!.pixelBufferPool!)!, &newPixelBuffer)
// Render the image to context
self.context.render(outputImage, to: newPixelBuffer!, bounds: outputImage.extent, colorSpace: nil)
// Setup a success case
let success = self.videoWriter?.assetWriterPixelBufferInput?.append(newPixelBuffer!, withPresentationTime: self.currentSampleTime!)
// Ensure the success case exists
guard let mySuccess = success else { return }
// If unsuccessful, log
if !mySuccess {
print("Error with the sample buffer. Check for dropped frames.")
}
}
}
}
}
I receive an error that newPixelBuffer is nil, but again, only on a 7.9" iPad. The iPad Pro functions without any errors. Any thoughts? Thanks!

Answer 1

I eventually resolved this issue by tracing the problem back to my chosen codec in my Asset Writer's video output settings. I had my codec set to:
let codec: AVVideoCodecType = AVVideoCodecType.hevc
In doing some research, I found this article, which indicates that only certain devices can capture media in HEVC. As my first device was a 10.5" iPad Pro, it captured media with no problem. My second device was an iPad Mini, which resulted in the original problem occurring each time I tried to capture.
I have since changed my codec choice to:
let codec: AVVideoCodecType = AVVideoCodecType.h264, and the issue has now disappeared.