AudioUnitSetProperty fails with -10868 when setting kAudioUnitProperty_StreamFormat to AAC

0
votes

I want to use the to encode the output of a AUGraph as AAC (on iOS 5.1). The basic topology of the graph looks like this:

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

I want to to grab the AAC-encoded data as it's playing via a PostRenderCallback on pcm2aac and then send it via UDP to our server application.

As I understand, the go-to AudioUnit for this use-case is kAudioUnitType_FormatConverter, but when I want to set the ASBD Input Property for aac2pcm, AudioUnitSetProperty fails with -10868 (it also fails when I set the output of pcm2acc, with the same error).

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

where aacStreamFormat is

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);

Are this kind of conversions even possible with AUGraph or do I have to use other methods for live conversion?

2
ioscore-audioaudiounitaac

2 Answers

0
votes

I don't think you need the pcm2aac and aac2pcm nodes. You could just install a render callback on your mixer node and use ExtAudioFileWriteAsync to save the output as AAC.

0
votes

Reference AUComponent.h

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

so you can't transcode pcm to aac by kAudioUnitSubType_AUConverter.

You shoulde use AudioConverter instead, here is the reference URL https://developer.apple.com/library/ios/samplecode/iPhoneACFileConvertTest/Introduction/Intro.html