I’m working with Apple’s MixerHost sample project, which sets up an audio unit processing graph consisting of a multichannel mixer audio unit connected to a remote I/O audio unit. I’m trying to put a format converter audio unit between the two so I can convert the format of the mixer’s output.
Copying the setup of the two existing audio units seems straightforward, and when I output the graph setup it looks right:
Member Nodes:
node 1: 'auou' 'rioc' 'appl', instance 0x1cdf10 O
node 2: 'aufc' 'conv' 'appl', instance 0x1ce890 O
node 3: 'aumx' 'mcmx' 'appl', instance 0x1ceba0 O
Connections:
node 3 bus 0 => node 2 bus 1
node 2 bus 0 => node 1 bus 0 [ 2 ch, 0 Hz, 'lpcm' (0x0000000C) 16-bit little-endian signed integer]
However, when I initialize the graph, I get error -10877, Invalid Element, and the graph doesn’t start up. Can anyone see what’s wrong? Here’s the complete setup code:
NSLog (@"Configuring and then initializing audio processing graph");
OSStatus result = noErr;
//............................................................................
// Create a new audio processing graph.
result = NewAUGraph (&processingGraph);
if (noErr != result) {[self printErrorMessage: @"NewAUGraph" withStatus: result]; return;}
//............................................................................
// Specify the audio unit component descriptions for the audio units to be
// added to the graph.
// I/O unit
AudioComponentDescription ioUnitDescription;
ioUnitDescription.componentType = kAudioUnitType_Output;
ioUnitDescription.componentSubType = kAudioUnitSubType_RemoteIO;
ioUnitDescription.componentManufacturer = kAudioUnitManufacturer_Apple;
ioUnitDescription.componentFlags = 0;
ioUnitDescription.componentFlagsMask = 0;
// Converter unit
AudioComponentDescription ConverterUnitDescription;
ConverterUnitDescription.componentType = kAudioUnitType_FormatConverter;
ConverterUnitDescription.componentSubType = kAudioUnitSubType_AUConverter;
ConverterUnitDescription.componentManufacturer = kAudioUnitManufacturer_Apple;
ConverterUnitDescription.componentFlags = 0;
ConverterUnitDescription.componentFlagsMask = 0;
// Multichannel mixer unit
AudioComponentDescription MixerUnitDescription;
MixerUnitDescription.componentType = kAudioUnitType_Mixer;
MixerUnitDescription.componentSubType = kAudioUnitSubType_MultiChannelMixer;
MixerUnitDescription.componentManufacturer = kAudioUnitManufacturer_Apple;
MixerUnitDescription.componentFlags = 0;
MixerUnitDescription.componentFlagsMask = 0;
//............................................................................
// Add nodes to the audio processing graph.
NSLog (@"Adding nodes to audio processing graph");
AUNode mixerNode; // node for Multichannel Mixer unit
AUNode converterNode; // node for AU Converter unit
AUNode ioNode; // node for I/O unit
// Add the nodes to the audio processing graph
result = AUGraphAddNode (
processingGraph,
&ioUnitDescription,
&ioNode);
if (noErr != result) {[self printErrorMessage: @"AUGraphNewNode failed for I/O unit" withStatus: result]; return;}
result = AUGraphAddNode (
processingGraph,
&ConverterUnitDescription,
&converterNode
);
if (noErr != result) {[self printErrorMessage: @"AUGraphNewNode failed for Converter unit" withStatus: result]; return;}
result = AUGraphAddNode (
processingGraph,
&MixerUnitDescription,
&mixerNode
);
if (noErr != result) {[self printErrorMessage: @"AUGraphNewNode failed for Mixer unit" withStatus: result]; return;}
//............................................................................
// Open the audio processing graph
// Following this call, the audio units are instantiated but not initialized
// (no resource allocation occurs and the audio units are not in a state to
// process audio).
result = AUGraphOpen (processingGraph);
if (noErr != result) {[self printErrorMessage: @"AUGraphOpen" withStatus: result]; return;}
//............................................................................
// Obtain the audio unit instances from their corresponding nodes.
AudioUnit mixerUnit;
AudioUnit converterUnit;
AudioUnit ioUnit;
result = AUGraphNodeInfo (
processingGraph,
ioNode,
NULL,
&ioUnit
);
if (noErr != result) {[self printErrorMessage: @"AUGraphNodeInfo" withStatus: result]; return;}
result = AUGraphNodeInfo (
processingGraph,
converterNode,
NULL,
&converterUnit
);
if (noErr != result) {[self printErrorMessage: @"AUGraphNodeInfo" withStatus: result]; return;}
result = AUGraphNodeInfo (
processingGraph,
mixerNode,
NULL,
&mixerUnit
);
if (noErr != result) {[self printErrorMessage: @"AUGraphNodeInfo" withStatus: result]; return;}
//............................................................................
// Audio Unit Setup
// Set the mixer unit's output sample rate format. This is the only aspect of the output stream
// format that must be explicitly set.
NSLog (@"Setting sample rate for mixer unit output scope");
result = AudioUnitSetProperty (
mixerUnit,
kAudioUnitProperty_SampleRate,
kAudioUnitScope_Output,
0,
&graphSampleRate,
sizeof (graphSampleRate)
);
if (noErr != result) {[self printErrorMessage: @"AudioUnitSetProperty (set mixer unit output stream format)" withStatus: result]; return;}
//............................................................................
// Connect the nodes of the audio processing graph
NSLog (@"Connecting the mixer output to the input of the converter unit input element");
result = AUGraphConnectNodeInput (
processingGraph,
mixerNode, // source node
0, // source node output bus number
converterNode, // destination node
1 // destination node input bus number
);
if (noErr != result) {[self printErrorMessage: @"AUGraphConnectNodeInput" withStatus: result]; return;}
NSLog (@"Connecting the converter output to the input of the I/O unit output element");
result = AUGraphConnectNodeInput (
processingGraph,
converterNode, // source node
0, // source node output bus number
ioNode, // destination node
0 // destination node input bus number
);
if (noErr != result) {[self printErrorMessage: @"AUGraphConnectNodeInput" withStatus: result]; return;}
//............................................................................
// Initialize audio processing graph
// Diagnostic code
// Call CAShow if you want to look at the state of the audio processing
// graph.
NSLog (@"Audio processing graph state immediately before initializing it:");
CAShow (processingGraph);
NSLog (@"Initializing the audio processing graph");
// Initialize the audio processing graph, configure audio data stream formats for
// each input and output, and validate the connections between audio units.
result = AUGraphInitialize (processingGraph);
if (noErr != result) {[self printErrorMessage: @"AUGraphInitialize" withStatus: result]; return;}
I just found an answer! Here’s the problem:
The stream format isn’t defined, so something is wrong.
I haven’t tested this on the AUConverter unit, but with the iPodEQ unit you use only one element. Then, you connect the mixer output to the input scope of the output bus, i.e.
HTH. 🙂