我正在使用一个iOS应用程序,它使用AVAudioEngine进行各种操作,包括将音频录制到文件,使用音频单元对该音频应用效果,并使用应用的效果播放音频.我用一个tap也可以将输出写入一个文件.当这样做完成时,它会在音频播放时实时写入文件.
可以设置从文件读取的AVAudioEngine图形,使用音频单元处理声音,并将其输出到文件,但是比实时更快(即,与硬件一样快)？这样做的用例是输出几分钟的音频并应用效果,我当然不想等待几分钟才能被处理.
编辑：这里是我用来设置AVAudioEngine的图形的代码,并播放一个声音文件：
AVAudioEngine* engine = [[AVAudioEngine alloc] init]; AVAudioPlayerNode* player = [[AVAudioPlayerNode alloc] init]; [engine attachNode:player]; self.player = player; self.engine = engine; if (!self.distortionEffect) { self.distortionEffect = [[AVAudioUnitDistortion alloc] init]; [self.engine attachNode:self.distortionEffect]; [self.engine connect:self.player to:self.distortionEffect format:[self.distortionEffect outputFormatForBus:0]]; AVAudioMixerNode* mixer = [self.engine mainMixerNode]; [self.engine connect:self.distortionEffect to:mixer format:[mixer outputFormatForBus:0]]; } [self.distortionEffect loadFactoryPreset:AVAudioUnitDistortionPresetDrumsBitBrush]; NSError* error; if (![self.engine startAndReturnError:&error]) { NSLog(@"error: %@",error); } else { NSURL* fileURL = [[NSBundle mainBundle] URLForResource:@"test2" withExtension:@"mp3"]; AVAudioFile* file = [[AVAudioFile alloc] initForReading:fileURL error:&error]; if (error) { NSLog(@"error: %@",error); } else { [self.player scheduleFile:file atTime:nil completionHandler:nil]; [self.player play]; } }
上述代码播放test2.mp3文件中的声音,并实时应用AVAudioUnitDistortionPresetDrumsBitBrush失真预设.
然后我通过在[self.player play]之后添加这些行来修改上面的代码：
[self.engine stop];
[self renderAudioAndWriteToFile];
我修改了Vladimir提供的renderAudioAndWriteToFile方法,而不是在第一行分配一个新的AVAudioEngine,它只是使用已经设置的self.engine.
但是,在renderAudioAndWriteToFile中,由于AudioUnitRender返回kAudioUnitErr_Uninitialized的状态,因此它记录“无法渲染音频单元”.
编辑2：我应该提到,我非常高兴转换我发布的AVAudioEngine代码使用C apis,如果这将使事情变得更容易.但是,我希望代码产生与AVAudioEngine代码相同的输出(包括使用上面显示的出厂预设).
解决方法
>配置您的引擎和播放器节点.
>您的播放器节点的通话播放方式.
>暂停引擎.
>从AVAudioOutputNode(audioEngine.outputNode)获取音频单元
用这个 method.
>从 AudioUnitRender的音频单元渲染循环,并将音频缓冲区列表写入 Extended Audio File Services文件.
>您的播放器节点的通话播放方式.
>暂停引擎.
>从AVAudioOutputNode(audioEngine.outputNode)获取音频单元
用这个 method.
>从 AudioUnitRender的音频单元渲染循环,并将音频缓冲区列表写入 Extended Audio File Services文件.
例：
音频引擎配置
- (void)configureAudioEngine { self.engine = [[AVAudioEngine alloc] init]; self.playerNode = [[AVAudioPlayerNode alloc] init]; [self.engine attachNode:self.playerNode]; AVAudioUnitDistortion *distortionEffect = [[AVAudioUnitDistortion alloc] init]; [self.engine attachNode:distortionEffect]; [self.engine connect:self.playerNode to:distortionEffect format:[distortionEffect outputFormatForBus:0]]; self.mixer = [self.engine mainMixerNode]; [self.engine connect:distortionEffect to:self.mixer format:[self.mixer outputFormatForBus:0]]; [distortionEffect loadFactoryPreset:AVAudioUnitDistortionPresetDrumsBitBrush]; NSError* error; if (![self.engine startAndReturnError:&error]) NSLog(@"Can't start engine: %@",error); else [self scheduleFileToPlay]; } - (void)scheduleFileToPlay { NSError* error; NSURL *fileURL = [[NSBundle mainBundle] URLForResource:@"filename" withExtension:@"m4a"]; self.file = [[AVAudioFile alloc] initForReading:fileURL error:&error]; if (self.file) [self.playerNode scheduleFile:self.file atTime:nil completionHandler:nil]; else NSLog(@"Can't read file: %@",error); }
呈现方式
- (void)renderAudioAndWriteToFile { [self.playerNode play]; [self.engine pause]; 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; AVURLAsset *asset = [AVURLAsset assetWithURL:self.file.url]; NSTimeInterval duration = CMTimeGetSeconds(asset.duration); NSUInteger lengthInFrames = duration * audioDescription->mSampleRate; const NSUInteger kBufferLength = 4096; AudioBufferList *bufferList = AEAllocateAndInitAudioBufferList(*audioDescription,kBufferLength); AudioTimeStamp timeStamp; memset (&timeStamp,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,restBufferLength); status = [self renderToBufferList:restBufferList writeToFile:audioFile bufferLength:restBufferLength timeStamp:&timeStamp]; AEFreeAudioBufferList(restBufferList); } AEFreeAudioBufferList(bufferList); ExtAudioFileDispose(audioFile); if (status != noErr) NSLog(@"An error has occurred"); else NSLog(@"Finished writing to file at path: %@",path); } - (NSString *)filePath { NSArray *documentsFolders = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask,YES); NSString *fileName = [NSString stringWithFormat:@"%@.m4a",[[NSUUID UUID] UUIDString]]; NSString *path = [documentsFolders[0] stringByAppendingPathComponent:fileName]; return path; } - (ExtAudioFileRef)createAndSetupExtAudioFileWithASBD:(AudioStreamBasicDescription const *)audioDescription andFilePath:(NSString *)path { AudioStreamBasicDescription destinationFormat; memset(&destinationFormat,sizeof(destinationFormat)); destinationFormat.mChannelsPerFrame = audioDescription->mChannelsPerFrame; destinationFormat.mSampleRate = audioDescription->mSampleRate; destinationFormat.mFormatID = kAudioFormatMPEG4AAC; ExtAudioFileRef audioFile; OSStatus status = ExtAudioFileCreateWithURL( (__bridge CFURLRef) [NSURL fileURLWithPath:path],kAudioFileM4AType,&destinationFormat,NULL,kAudioFileFlags_EraseFile,&audioFile ); if (status != noErr) { NSLog(@"Can not create ext audio file"); return nil; } UInt32 codecManufacturer = kAppleSoftwareAudioCodecManufacturer; status = ExtAudioFileSetProperty( audioFile,kExtAudioFileProperty_CodecManufacturer,sizeof(UInt32),&codecManufacturer ); status = ExtAudioFileSetProperty( audioFile,kExtAudioFileProperty_ClientDataFormat,sizeof(AudioStreamBasicDescription),audioDescription ); status = ExtAudioFileWriteAsync(audioFile,NULL); if (status != noErr) { NSLog(@"Can not setup ext audio file"); return nil; } return audioFile; } - (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,timeStamp,bufferLength,bufferList); if (status != noErr) { NSLog(@"Can not render audio unit"); return status; } timeStamp->mSampleTime += bufferLength; status = ExtAudioFileWrite(audioFile,bufferList); if (status != noErr) NSLog(@"Can not write audio to file"); return status; } - (void)clearBufferList:(AudioBufferList *)bufferList { for (int bufferIndex = 0; bufferIndex < bufferList->mNumberBuffers; bufferIndex++) { memset(bufferList->mBuffers[bufferIndex].mData,bufferList->mBuffers[bufferIndex].mDataByteSize); } }
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; } void AEFreeAudioBufferList(AudioBufferList *bufferList ) { for ( int i=0; i<bufferList->mNumberBuffers; i++ ) { if ( bufferList->mBuffers[i].mData ) free(bufferList->mBuffers[i].mData); } free(bufferList); }
