Video compression using AVAssetWriter - ios

Question

I've created a function to compress a video file. It uses AVAssetWriter and adds inputs and outputs for video and audio tracks. When it starts writing I'm getting an error when the AVAssetReader for the audio track starts reading, audioReader.startReading(). Here the error, *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[AVAssetReader startReading] cannot be called again after reading has already started'.
The code: https://gist.github.com/jaumevn/9ba329aaf49c81c57a276fd135f53f20
Can anyone see what's the problem here? Thanks!

Answer 1

Line 77 of your code, you're starting a second AVAssetReader on the same file.
You don't need to hook up two readers, instead, you should hook up your AVAudioAssetReader as an Output for the existing AVAssetReader.
Something like this:
let videoReaderSettings : [String : Int] = [kCVPixelBufferPixelFormatTypeKey as String : Int(kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange)]
let videoReaderOutput = AVAssetReaderTrackOutput(track: videoAssetTrack, outputSettings: videoReaderSettings)
let videoReader = try! AVAssetReader(asset: videoAssetUrl)
var settings = [String : AnyObject]()
settings[AVFormatIDKey] = Int(kAudioFormatLinearPCM)
let audioReaderOutput = AVAssetReaderTrackOutput(track: audioAssetTrack, outputSettings: settings)
videoReader.addOutput(videoReaderOutput)
videoReader.addOutput(audioReaderOutput)
videoWriter.startWriting()
videoReader.startReading()
Look into using AVCaptureVideoDataOutputSampleBufferDelegate and AVCaptureAudioDataOutputSampleBufferDelegate to capture and process the buffers from the reader.