AVAssetReader/Writer only working on certain devices? - objective-c

Question

I was using this tutorial to get a song from the music library to my specified directory. It works fine for me, but other people are reporting that the song never gets there. At first I thought there were device limitations, but it seems like people with the same device as me are having the problem. It is sort of annoying because I can't recreate their problem.
Here is my code:
{
NSURL *assetURL = [song valueForProperty:MPMediaItemPropertyAssetURL];
AVURLAsset *songAsset = [AVURLAsset URLAssetWithURL:assetURL options:nil];
NSError *assetError = nil;
AVAssetReader *assetReader = [[AVAssetReader assetReaderWithAsset:songAsset
error:&assetError]
retain];
if (assetError) {
NSLog (#"error: %#", assetError);
return;
}
AVAssetReaderOutput *assetReaderOutput = [[AVAssetReaderAudioMixOutput
assetReaderAudioMixOutputWithAudioTracks:songAsset.tracks
audioSettings: nil]
retain];
if (! [assetReader canAddOutput: assetReaderOutput]) {
NSLog (#"can't add reader output... die!");
return;
}
[assetReader addOutput: assetReaderOutput];
NSString *exportPath = #"Library/PreferenceBundles/MyAlarmSettings.bundle/export.m4a";
if ([[NSFileManager defaultManager] fileExistsAtPath:exportPath]) {
[[NSFileManager defaultManager] removeItemAtPath:exportPath error:nil];
}
NSURL *exportURL = [NSURL fileURLWithPath:exportPath];
AVAssetWriter *assetWriter = [[AVAssetWriter assetWriterWithURL:exportURL
fileType:AVFileTypeAppleM4A
error:&assetError]
retain];
if (assetError) {
NSLog (#"error: %#", assetError);
return;
}
AudioChannelLayout channelLayout;
memset(&channelLayout, 0, sizeof(AudioChannelLayout));
channelLayout.mChannelLayoutTag = kAudioChannelLayoutTag_Stereo;
NSDictionary *outputSettings = [NSDictionary dictionaryWithObjectsAndKeys:
[ NSNumber numberWithInt: kAudioFormatMPEG4AAC], AVFormatIDKey,
[ NSNumber numberWithInt: 2 ], AVNumberOfChannelsKey,
[ NSNumber numberWithFloat: 44100.0 ], AVSampleRateKey,
[ NSData dataWithBytes:&channelLayout length: sizeof( AudioChannelLayout ) ], AVChannelLayoutKey,
[ NSNumber numberWithInt: 320000 ], AVEncoderBitRateKey,
nil];
AVAssetWriterInput *assetWriterInput = [[AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeAudio
outputSettings:outputSettings]
retain];
if ([assetWriter canAddInput:assetWriterInput]) {
[assetWriter addInput:assetWriterInput];
} else {
NSLog (#"can't add asset writer input... die!");
return;
}
assetWriterInput.expectsMediaDataInRealTime = NO;
[assetWriter startWriting];
[assetReader startReading];
AVAssetTrack *soundTrack = [songAsset.tracks objectAtIndex:0];
CMTime startTime = CMTimeMake (0, soundTrack.naturalTimeScale);
[assetWriter startSessionAtSourceTime: startTime];
__block UInt64 convertedByteCount = 0;
dispatch_queue_t mediaInputQueue = dispatch_queue_create("mediaInputQueue", NULL);
[assetWriterInput requestMediaDataWhenReadyOnQueue:mediaInputQueue
usingBlock: ^
{
// NSLog (#"top of block");
while (assetWriterInput.readyForMoreMediaData) {
CMSampleBufferRef nextBuffer = [assetReaderOutput copyNextSampleBuffer];
if (nextBuffer) {
// append buffer
[assetWriterInput appendSampleBuffer: nextBuffer];
// NSLog (#"appended a buffer (%d bytes)",
// CMSampleBufferGetTotalSampleSize (nextBuffer));
convertedByteCount += CMSampleBufferGetTotalSampleSize (nextBuffer);
// oops, no
// sizeLabel.text = [NSString stringWithFormat: #"%ld bytes converted", convertedByteCount];
NSNumber *convertedByteCountNumber = [NSNumber numberWithLong:convertedByteCount];
[self performSelectorOnMainThread:#selector(updateSizeLabel:)
withObject:convertedByteCountNumber
waitUntilDone:NO];
} else {
// done!
NSString *songtitle = [[NSString alloc]initWithFormat:#"Alarm sound set to '%#' \n \n Press OK to respring. ",[song valueForProperty:MPMediaItemPropertyTitle]];
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"Done!" message:songtitle delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil];
[alert show];
[alert release];
[assetWriterInput markAsFinished];
[assetWriter finishWriting];
[assetReader cancelReading];
NSDictionary *outputFileAttributes = [[NSFileManager defaultManager]
attributesOfItemAtPath:exportPath
error:nil];
NSLog (#"done. file size is %llu",
[outputFileAttributes fileSize]);
NSNumber *doneFileSize = [NSNumber numberWithLong:[outputFileAttributes fileSize]];
[self performSelectorOnMainThread:#selector(updateCompletedSizeLabel:)
withObject:doneFileSize
waitUntilDone:NO];
// release a lot of stuff
[assetReader release];
[assetReaderOutput release];
[assetWriter release];
[assetWriterInput release];
[exportPath release];
break;
}
}
}];
NSLog (#"bottom of convertTapped:");
}

Answer 1

If you are accessing mediaItems from the users iPod library they maybe in the cloud. Use
[self.mediaItem valueForProperty:MPMediaItemPropertyIsCloudItem]
as far as I know you can not access these assets or force them to stream