Adding Audio to AVAsset - ios

Question

I've been attempting to use AVAssetWriter to crop and export a video in an iOS app. Everything has been going swimmingly up until I attempted to add audio to the output. The current code (see below) returns the following error
NSInvalidArgumentException', reason: '* -[AVAssetReader startReading] cannot be called again after reading has already started'
From what I've written below, this should be using a different reader than the one that was initialized, and so I don't understand the issue. This may be a simple issue of needing another pair of eyes on it, so here's the code.
-(void)cropVideoAsset:(NSURL *)fileURL
{
NSString *outputPath = [NSString stringWithFormat:#"%#%#", NSTemporaryDirectory(), #"croppedVideo.mov"];
toUrl = [NSURL fileURLWithPath:outputPath];
if([[NSFileManager defaultManager] fileExistsAtPath:outputPath])
{[[NSFileManager defaultManager] removeItemAtPath:outputPath error:nil];}
AVAsset *asset = [AVAsset assetWithURL:fileURL];
NSLog(#"asset: %f", CMTimeGetSeconds(asset.duration));
NSDictionary* compressionSettings = [NSDictionary dictionaryWithObjectsAndKeys:
AVVideoProfileLevelH264Main31, AVVideoProfileLevelKey,
[NSNumber numberWithInt:2500000], AVVideoAverageBitRateKey,
[NSNumber numberWithInt: 5], AVVideoMaxKeyFrameIntervalKey,
nil];
NSDictionary* videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
AVVideoCodecH264, AVVideoCodecKey,
[NSNumber numberWithInt:500], AVVideoWidthKey,
[NSNumber numberWithInt:500], AVVideoHeightKey,
AVVideoScalingModeResizeAspectFill, AVVideoScalingModeKey,
compressionSettings, AVVideoCompressionPropertiesKey,
nil];
AVAssetWriterInput *writerInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:videoSettings];
writerInput.expectsMediaDataInRealTime = true;
NSError *error;
AVAssetWriter *assetWriter = [AVAssetWriter assetWriterWithURL:toUrl fileType:AVFileTypeMPEG4 error:&error];
[assetWriter addInput:writerInput];
AVAssetReader *assetReader = [AVAssetReader assetReaderWithAsset:asset error:&error];
AVAssetTrack *videoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
writerInput.transform = videoTrack.preferredTransform;
NSDictionary *videoOptions = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange] forKey:(id)kCVPixelBufferPixelFormatTypeKey];
AVAssetReaderTrackOutput *asset_reader_output = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:videoTrack outputSettings:videoOptions];
[assetReader addOutput:asset_reader_output];
//audio setup
NSDictionary *audioSettings = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInt:kAudioFormatMPEG4AAC], AVFormatIDKey,
[NSNumber numberWithInt:1], AVNumberOfChannelsKey,
[NSNumber numberWithFloat:44100.0], AVSampleRateKey,
[NSNumber numberWithInt:64000], AVEncoderBitRateKey,
nil];
AVAssetWriterInput *audioWriterInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeAudio outputSettings:audioSettings];
AVAssetReader *audioReader = [AVAssetReader assetReaderWithAsset:asset error:&error];
AVAssetTrack *audioTrack = [[asset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
AVAssetReaderOutput *readerOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:audioTrack outputSettings:nil];
[audioReader addOutput:readerOutput];
audioWriterInput.expectsMediaDataInRealTime = true;
[assetWriter addInput:audioWriterInput];
[assetWriter startWriting];
[assetWriter startSessionAtSourceTime:kCMTimeZero];
[assetReader startReading];
dispatch_queue_t _processingQueue = dispatch_queue_create("assetAudioWriterQueue", NULL);
[writerInput requestMediaDataWhenReadyOnQueue:_processingQueue usingBlock:
^{
while(writerInput.readyForMoreMediaData)
{
switch(assetReader.status)
{
case AVAssetReaderStatusReading:
{
CMSampleBufferRef sampleBuffer = [asset_reader_output copyNextSampleBuffer];
if (sampleBuffer)
{
BOOL result = [writerInput appendSampleBuffer:sampleBuffer];
CFRelease(sampleBuffer);
if (!result)
{
[SVProgressHUD dismiss];
[self enableView];
NSString *errorMessage = [NSString stringWithFormat:#"We're sorry, an error occurred during the video capture.\n\n%#\n\nPlease try again.", assetWriter.error.localizedDescription];
[UIAlertView simpleAlertWithTitle:#"Video Error" andMessage:errorMessage];
[assetReader cancelReading];
break;
}
}
}
break;
case AVAssetReaderStatusCompleted:
{
[self handleAudioWithReader:audioReader writer:assetWriter input:audioWriterInput andOutput:readerOutput];
}
break;
case AVAssetReaderStatusFailed:
[SVProgressHUD dismiss];
[self enableView];
[UIAlertView simpleAlertWithTitle:#"Video Error" andMessage:#"We're sorry, an error occurred during the video capture. Please try again."];
[assetWriter cancelWriting];
break;
}
}
}];
}
and the requisite call
-(void)handleAudioWithReader:(AVAssetReader *)audioReader writer:(AVAssetWriter *)videoWriter input:(AVAssetWriterInput *)audioWriterInput andOutput:(AVAssetReaderOutput *)readerOutput
{
[audioReader startReading];
[videoWriter startSessionAtSourceTime:kCMTimeZero];
dispatch_queue_t mediaInputQueue = dispatch_queue_create("mediaInputQueue", NULL);
[audioWriterInput requestMediaDataWhenReadyOnQueue:mediaInputQueue usingBlock:^
{
NSLog(#"Asset Writer ready :%d", audioWriterInput.readyForMoreMediaData);
while (audioWriterInput.readyForMoreMediaData)
{
CMSampleBufferRef nextBuffer;
if([audioReader status] == AVAssetReaderStatusReading && (nextBuffer = [readerOutput copyNextSampleBuffer]))
{
if (nextBuffer)
{
NSLog(#"NextBuffer");
[audioWriterInput appendSampleBuffer:nextBuffer];
}
}
else
{
[audioWriterInput markAsFinished];
switch ([audioReader status])
{
case AVAssetReaderStatusCompleted:
[videoWriter finishWriting];
[audioWriterInput markAsFinished];
dispatch_async(dispatch_get_main_queue(),^{[self saveAssetToLibraryAtURL:toUrl];});
break;
}
}
}
}];
}