I am using ffmpeg to acquire audio from .mov files. Looking over my settings, I
am not sample rate converting the audio buffers I am generating so that is
unlikely to account for the issues I am having. Regardless of the sample rate I
set on my Built-in Output, my audio files that are at 44.1 kHz playback at the
correct rate. If I playback a 48kHz file, the file plays back slower (at 91% of
the normal rate) which indicates that the true rate is 44.1kHz. I can change my
built-in output to 44.1, 48, or 96 kHz and the same phenomenon exists. I
change my default output rate using the Audio Midi Setup app. I then verify my
sample rate using AudioUnitGetProperty on my ouputAudioUnit. This matches the
sample rate in the Audio Midi Setup.
Thoughts? I am including my audio graph code
CheckError(NewAUGraph(&fp.graph), "Couldn't create a new AUGraph");
//varispeednode has an input callback
//the vairspeed node feeds an output node which is running
//at the frequency of the system default output
AUNode outputNode;
AudioComponentDescription outputcd = [self defaultOutputComponent];
CheckError(AUGraphAddNode(fp.graph, &outputcd, &outputNode),
"AUGraphAddNode[kAudioUnitSubType_DefaultOutput] failed");
AUNode varispeedNode;
AudioComponentDescription varispeedcd = [self variSpeedComponent];
CheckError(AUGraphAddNode(fp.graph, &varispeedcd, &varispeedNode),
"AUGraphAddNode[kAudioUnitSubType_Varispeed] failed");
CheckError(AUGraphOpen(fp.graph),
"Couldn't Open AudioGraph");
CheckError(AUGraphNodeInfo(fp.graph, outputNode, NULL, &fp.outputAudioUnit),
"Couldn't Retrieve output node");
CheckError(AUGraphNodeInfo(fp.graph, varispeedNode, NULL,
&fp.variSpeedAudioUnit),
"Couldn't Retrieve Varispeed Audio Unit");
AURenderCallbackStruct input;
input.inputProc = CBufferProviderCallback;
input.inputProcRefCon = &playerStruct;
CheckError(AudioUnitSetProperty(fp.variSpeedAudioUnit,
kAudioUnitProperty_SetRenderCallback,
kAudioUnitScope_Input,
0,
&input,
sizeof(input)),
"AudioUnitSetProperty failed");
CheckError(AUGraphConnectNodeInput(fp.graph, varispeedNode, 0, outputNode, 0),
"Couldn't Connect varispeed to output");
CheckError(AUGraphInitialize(fp.graph),
"Couldn't Initialize AUGraph");
// check output sample rate
Float64 outputSampleRate = 48000.0;
UInt32 sizeOfFloat64 = sizeof(Float64);
outputSampleRate = 0.0;
CheckError(AudioUnitGetProperty(fp.outputAudioUnit,
kAudioUnitProperty_SampleRate,
kAudioUnitScope_Global,
0,
&outputSampleRate,
&sizeOfFloat64),
"Couldn't get output sampleRate");
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