There was a task - to save the output stream from AVAudioEngine to a file. There is little information on this subject on the Internet; the only solution found was taken from this topic:
https://stackoverflow.com/questions/3...-unit-and-writ
And everything would be fine, but on the iPad, as well as with the headphones connected in this method, AudioUnitRender writes zeros to the buffer of the list, respectively, a file of the desired length is created but with silence instead of music. Maybe someone found a solution to the problem?
Buffer initialization
AudioBufferList *AEAllocateAndInitAudioBufferList(AudioStreamBasicDescription audioFormat, int frameCount) { int numberOfBuffers = audioFormat.mFormatFlags & kAudioFormatFlagIsNonInterleaved ? audioFormat.mChannelsPerFrame : 1; int channelsPerBuffer = audioFormat.mFormatFlags & kAudioFormatFlagIsNonInterleaved ? 1 : audioFormat.mChannelsPerFrame; int bytesPerBuffer = audioFormat.mBytesPerFrame * frameCount; AudioBufferList *audio = malloc(sizeof(AudioBufferList) + (numberOfBuffers - 1) * sizeof(AudioBuffer)); if (!audio) { return NULL; } audio->mNumberBuffers = numberOfBuffers; for (int i = 0; i < numberOfBuffers; i++) { if (bytesPerBuffer > 0) { audio->mBuffers[i].mData = calloc(bytesPerBuffer, 1); if (!audio->mBuffers[i].mData) { for (int j = 0; j < i; j++) free(audio->mBuffers[j].mData); free(audio); return NULL; } } else { audio->mBuffers[i].mData = NULL; } audio->mBuffers[i].mDataByteSize = bytesPerBuffer; audio->mBuffers[i].mNumberChannels = channelsPerBuffer; } return audio;} Rendering method
- (OSStatus)renderToBufferList:(AudioBufferList *)bufferList writeToFile:(ExtAudioFileRef)audioFile bufferLength:(NSUInteger)bufferLength timeStamp:(AudioTimeStamp *)timeStamp { [self clearBufferList:bufferList]; AudioUnit outputUnit = self.engine.outputNode.audioUnit; OSStatus status =AudioUnitRender(outputUnit, 0, timeStamp, 0, (UInt32)bufferLength, bufferList); float *data1 = bufferList->mBuffers[0].mData; float *data2 = bufferList->mBuffers[1].mData;; for(int i=0; i<bufferLength/4; i++) { if(data1[i]!=0||data2[i]!=0) NSLog(@"%f - %f",data1[i],data2[i]); } if (status != noErr) { NSLog(@"Can not render audio unit"); return status; } timeStamp->mSampleTime += bufferLength; status = ExtAudioFileWrite(audioFile, (UInt32)bufferLength, bufferList); if (status != noErr) NSLog(@"Can not write audio to file"); The main method from which the above are called
- (NSString *)renderAudioAndWriteToFile { AVAudioOutputNode *outputNode = self.engine.outputNode; AudioStreamBasicDescription const *audioDescription = [outputNode outputFormatForBus:0].streamDescription; NSString *path = [self filePath]; ExtAudioFileRef audioFile = [self createAndSetupExtAudioFileWithASBD:audioDescription andFilePath:path]; if (!audioFile) return nil; AVURLAsset *asset = [AVURLAsset assetWithURL:self.file.url]; NSTimeInterval duration = CMTimeGetSeconds(asset.duration); NSUInteger lengthInFrames = (NSUInteger) (duration * audioDescription->mSampleRate); const NSUInteger kBufferLength = 1024; //3756; AudioBufferList *bufferList = AEAllocateAndInitAudioBufferList(*audioDescription, kBufferLength); AudioTimeStamp timeStamp; memset (&timeStamp, 0, sizeof(timeStamp)); timeStamp.mFlags = kAudioTimeStampSampleTimeValid; OSStatus status = noErr; for (NSUInteger i = kBufferLength; i < lengthInFrames; i += kBufferLength) { status = [self renderToBufferList:bufferList writeToFile:audioFile bufferLength:kBufferLength timeStamp:&timeStamp]; if (status != noErr) break; } if (status == noErr && timeStamp.mSampleTime < lengthInFrames) { NSUInteger restBufferLength = (NSUInteger) (lengthInFrames - timeStamp.mSampleTime); AudioBufferList *restBufferList = AEAllocateAndInitAudioBufferList(*audioDescription, (Float32)restBufferLength); status = [self renderToBufferList:restBufferList writeToFile:audioFile bufferLength:restBufferLength timeStamp:&timeStamp]; AEFreeAudioBufferList(restBufferList); } SInt64 fileLengthInFrames; UInt32 size = sizeof(SInt64); ExtAudioFileGetProperty(audioFile, kExtAudioFileProperty_FileLengthFrames, &size, &fileLengthInFrames); AEFreeAudioBufferList(bufferList); ExtAudioFileDispose(audioFile); if (status != noErr) [self showAlertWithTitle:@"Error" message:@"See logs for details"]; else { NSLog(@"Finished writing to file at path: %@ \n File size must be %f Mb", path,(tmpData.length/1024.0)/1024.0); [self showAlertWithTitle:@"Success!" message:@"Now you can play a result file"]; } return path; } 
