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POWriting and encoding remote I/0 output to file - Core Audio
 

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  1. POWriting and encoding remote I/0 output to file - Core Audio
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    <p>I'm coding a music recording app using Audio Units and I'm having some issues getting my resulting M4A file to play anything other than a not so awesome buzzing noise. I've used these SO <a href="https://stackoverflow.com/questions/10113977/recording-to-aac-from-remoteio-data-is-getting-written-but-file-unplayable">sources</a> <a href="https://stackoverflow.com/questions/8615358/can-anybody-help-me-in-recording-iphone-output-sound-through-audio-unit">as</a> <a href="https://stackoverflow.com/questions/7118429/how-to-record-sound-produced-by-mixer-unit-output-ios-core-audio-audio-graph">references</a>, and I've tried everything to troubleshoot.</p> <p>I've got an <code>AUGraph</code> with 2 nodes: a multi channel mixer and a remote I/O. I've got two input callbacks on my mixer: one that pulls input from the mic, and one that pulls from an audio file. The mixer output is connected to the input element of the output scope on the I/O unit. This enables simultaneous I/O.</p> <p>To capture the output I've added a callback and two methods:</p> <p><strong>The callback</strong></p> <pre><code>static OSStatus recordAndSaveCallback (void * inRefCon, AudioUnitRenderActionFlags * ioActionFlags, const AudioTimeStamp * inTimeStamp, UInt32 inBusNumber, UInt32 inNumberFrames, AudioBufferList * ioData) { Mixer* THIS = (__bridge Mixer*)inRefCon; AudioBufferList bufferList; OSStatus status; status = AudioUnitRender(THIS.ioUnit, ioActionFlags, inTimeStamp, 0, inNumberFrames, &amp;bufferList); SInt16 samples[inNumberFrames]; // A large enough size to not have to worry about buffer overrun memset (&amp;samples, 0, sizeof (samples)); bufferList.mNumberBuffers = 1; bufferList.mBuffers[0].mData = samples; bufferList.mBuffers[0].mNumberChannels = 1; bufferList.mBuffers[0].mDataByteSize = inNumberFrames*sizeof(SInt16); OSStatus result; if (*ioActionFlags == kAudioUnitRenderAction_PostRender) { result = ExtAudioFileWriteAsync(THIS.extAudioFileRef, inNumberFrames, &amp;bufferList); if(result) printf("ExtAudioFileWriteAsync %ld \n", result);} return noErr; } </code></pre> <p><strong>Recording Method:</strong></p> <pre><code>- (void)recordFile { OSStatus result; NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [paths objectAtIndex:0]; NSString *recordFile = [documentsDirectory stringByAppendingPathComponent: @"audio.m4a"]; CFURLRef destinationURL = CFURLCreateWithFileSystemPath(kCFAllocatorDefault, (__bridge CFStringRef)recordFile, kCFURLPOSIXPathStyle, false); AudioStreamBasicDescription destinationFormat; memset(&amp;destinationFormat, 0, sizeof(destinationFormat)); destinationFormat.mChannelsPerFrame = 1; destinationFormat.mFormatID = kAudioFormatMPEG4AAC; UInt32 size = sizeof(destinationFormat); result = AudioFormatGetProperty(kAudioFormatProperty_FormatInfo, 0, NULL, &amp;size, &amp;destinationFormat); if(result) printf("AudioFormatGetProperty %ld \n", result); result = ExtAudioFileCreateWithURL(destinationURL, kAudioFileM4AType, &amp;destinationFormat, NULL, kAudioFileFlags_EraseFile, &amp;extAudioFileRef); if(result) printf("ExtAudioFileCreateWithURL %ld \n", result); AudioStreamBasicDescription clientFormat; memset(&amp;clientFormat, 0, sizeof(clientFormat)); UInt32 clientsize = sizeof(clientFormat); result = AudioUnitGetProperty(ioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, 0, &amp;clientFormat, &amp;clientsize); if(result) printf("AudioUnitGetProperty %ld \n", result); UInt32 codec = kAppleHardwareAudioCodecManufacturer; result = ExtAudioFileSetProperty(extAudioFileRef, kExtAudioFileProperty_CodecManufacturer, sizeof(codec), &amp;codec); if(result) printf("ExtAudioFileSetProperty %ld \n", result); result = ExtAudioFileSetProperty(extAudioFileRef,kExtAudioFileProperty_ClientDataFormat,sizeof(clientFormat), &amp;clientFormat); if(result) printf("ExtAudioFileSetProperty %ld \n", result); result = ExtAudioFileWriteAsync(extAudioFileRef, 0, NULL); if (result) {[self printErrorMessage: @"ExtAudioFileWriteAsync error" withStatus: result];} result = AudioUnitAddRenderNotify(ioUnit, recordAndSaveCallback, (__bridge void*)self); if (result) {[self printErrorMessage: @"AudioUnitAddRenderNotify" withStatus: result];} } </code></pre> <p><strong>Saving Method:</strong></p> <pre><code>- (void) saveFile { OSStatus status = ExtAudioFileDispose(extAudioFileRef); NSLog(@"OSStatus(ExtAudioFileDispose): %ld\n", status); } </code></pre> <p><strong>This is what I see in my console:</strong> </p> <pre><code>Stopping audio processing graph OSStatus(ExtAudioFileDispose): 0 ExtAudioFileWriteAsync -50 ExtAudioFileWriteAsync -50 ExtAudioFileWriteAsync -50 </code></pre> <p>It seems to me that my code is very similar to that of people who have gotten this to work, but clearly I've made a crucial error. I'm sure there must be others struggling with this.</p> <p>Does anyone have any insight?</p> <p>Thanks.</p>
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    1. COIt looks like your `-saveFile` method is being called before `recordAndSaveCallback` is finished. Are you stopping the AUGraph before calling saveFile?
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    2. COas an experiment to rule out any issues with your graph it might be a good idea to try and record using a simpler format such as wav. ASBD can be hard to get right, but if you can determine that the ASBD is the problem(my opinion) then at least you can just focus on experimenting with the file format.
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    3. COrunning macerror -50 from the command line gives this: Mac OS error -50 (paramErr): error in user parameter list
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