AVPlayerItemVideoOutput file cannot be used in AVComposition IOS7 - objective-c

Question

I have a fully working app in IOS6 that breaks in IOS7 when using AVComposition.
Here is the problem:
In a previous view controller, I capture the users screen using AVPlayerItemVideoOutput & AVAssetWriterInputPixelBufferAdaptor to generate a video output file. In my current view controller, I take that generated video file and add it to an AVComposition to generate a video composition between this file and some audio. In IOS6, this process works perfectly, and the AVExportSession completes. In IOS7, the export process does not complete (the finish handler is never called and status is always AVAssetExportSessionStatusExporting).
Here is my pseudocode:
AVURLAsset *asset = [AVURLAsset URLAssetWithURL:self.metaInfo.videoCaptureFile options:nil];
AVMutableComposition* mixComposition = [[AVMutableComposition alloc] init];
AVMutableCompositionTrack *track = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
[track insertTimeRange:CMTimeRangeMake(kCMTimeZero, firstAsset.duration) ofTrack:[[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:kCMTimeZero error:&error];
AVMutableCompositionTrack *audioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
[audioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, secondAsset.duration) ofTrack:[[audioAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:kCMTimeZero error:&error];
AVMutableVideoCompositionInstruction * MainInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
/// Code for processing the composition
AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPreset640x480];
// Code for setting up exporter
[exporter exportAsynchronouslyWithCompletionHandler:^
{
dispatch_async(dispatch_get_main_queue(), ^{
[self exportDidFinished:exporter];
});
}];
After debugging my code, the problem came down to the generated video file that was being used. If I change asset to a hardcoded file, the exporter completes. What's interesting is that the video file that is generated from AVPlayerItemVideoOutput plays fine in a MPMoviePlayerViewController. Did something change with AVPlayerItemVideoOutput or AVAssetWriterInputPixelBufferAdaptor in IOS7 that would prevent the output file from being used in a composition? Do I need to add additional specifications in the composition? Does it have to deal with different frame rates?
Thanks for the help!

Answer 1

This is likely a low storage space issue specific to your test device where the AVAssetExportSession cannot write the final movie asset (or some intermediate data) to disk. I would check that the problem exists on other devices. I had the same problem on an iPhone 4 (iOS 7) but not on an iPad 2 (iOS 7) when working with a common build.