Question

我想使用它来编码AUGraph的输出作为AAC（在iOS 5.1上）。图的基本拓扑如下所示：

inputs --> MixerUnit --> pcm2aac --> aac2pcm --> RemoteIO

我希望在pcm2aac上通过PostRenderCallback播放AAC编码的数据，然后通过UDP将其发送到我们的服务器应用程序。

据我所知，这个用例的首选AudioUnit是kAudioUnitType_FormatConverter，但是当我想为aac2pcm设置ASBD输入属性时，AudioUnitSetProperty会失败并显示-10868（当我设置它时它也会失败pcm2acc的输出，具有相同的错误。）

AudioComponentDescription converterUnitDescription;
converterUnitDescription.componentType          = kAudioUnitType_FormatConverter;
converterUnitDescription.componentSubType       = kAudioUnitSubType_AUConverter;
converterUnitDescription.componentManufacturer  = kAudioUnitManufacturer_Apple;
converterUnitDescription.componentFlags         = 0;
converterUnitDescription.componentFlagsMask     = 0;
//...
AUNode   pcm2aacNode;
AUNode   aac2pcmNode;
//...
result =    AUGraphAddNode (
                            processingGraph,
                            &converterUnitDescription,
                            &aac2pcmNode
                            );

if (noErr != result) {[self printErrorMessage: @"AUGraphNewNode failed for Converter unit" withStatus: result]; return;}
//...
result = AUGraphOpen (processingGraph);

if (noErr != result) {[self printErrorMessage: @"AUGraphOpen" withStatus: result]; return;}

//...
AudioUnit aac2pcmUnit;
AudioUnit pcm2aacUnit;
//...
result =    AUGraphNodeInfo (
                             processingGraph,
                             aac2pcmNode,
                             NULL,
                             &aac2pcmUnit
                             );

if (noErr != result) {[self printErrorMessage: @"AUGraphNodeInfo (aac2pcm)" withStatus: result]; return;}

//...
NSLog (@"Setting stream format for input aac2pcm  bus");
result = AudioUnitSetProperty (aac2pcmUnit,
                               kAudioUnitProperty_StreamFormat,
                               kAudioUnitScope_Input,
                               0,
                               &aacStreamFormat,
                               sizeof (aacStreamFormat)
                               );

if (noErr != result) {[self printErrorMessage: @"AudioUnitSetProperty (input aac2pcm stream format)" withStatus: result];return;}
// returns -10868

其中aacStreamFormat是

memset(&aacStreamFormat, 0, sizeof(aacStreamFormat));/
UInt32 size = sizeof(aacStreamFormat);
aacStreamFormat.mFormatID          = kAudioFormatMPEG4AAC;
aacStreamFormat.mChannelsPerFrame  = 2;   
aacStreamFormat.mFormatFlags       = kMPEG4Object_AAC_Main;
aacStreamFormat.mSampleRate        = graphSampleRate; //44100
AudioFormatGetProperty(kAudioFormatProperty_FormatInfo, 0, NULL, &size, &aacStreamFormat);

AUGraph甚至可以进行这种转换，还是必须使用其他方法进行实时转换？

Answer 1

我认为您不需要pcm2aac和aac2pcm节点。您可以在混音器节点上安装渲染回调，并使用ExtAudioFileWriteAsync将输出保存为AAC。

Answer 2

参考AUComponent.h

kAudioUnitSubType_AUConverter
An audio unit that uses an AudioConverter to do Linear PCM conversions 
(sample rate, bit depth, interleaving).

所以你不能通过kAudioUnitSubType_AUConverter将pcm转码为aac。

您应该使用AudioConverter，这是参考URL https://developer.apple.com/library/ios/samplecode/iPhoneACFileConvertTest/Introduction/Intro.html

将KAudioUnitProperty_StreamFormat设置为AAC时，AudioUnitSetProperty以-10868失败

2 个答案: