PCM Data format with fmod - difference on multiple paltforms - audio

Question

I am writing a Unity3D plugin that reads data from an MP3 file, feeds the PCM data to Unity so that it can play it inside the engine. On iOS, I use the AVAssetReaderAudioMixOutput class to decode and read the data, and on Android/Windows, I use FMOD.
I have set up a program on both Windows and iOS which uses FMOD to play back the music, just like Unity3D does.
I am having trouble getting the same results on both iOS and windows, and I cant seem to find the difference in audio output settings/format that would cause the difference.
So first, these are the settings that I set for my output audio stream, which are the same settings as Unity3D uses:
FMOD_CREATESOUNDEXINFO exinfo2;
memset(&exinfo2, 0, sizeof(FMOD_CREATESOUNDEXINFO));
exinfo2.cbsize = sizeof(FMOD_CREATESOUNDEXINFO);
exinfo2.decodebuffersize = 44100;
exinfo2.length = 44100 * 1 * sizeof(float) * 100;
exinfo2.numchannels = 1;
exinfo2.defaultfrequency = 44100;
exinfo2.format = FMOD_SOUND_FORMAT_PCMFLOAT;
exinfo2.pcmreadcallback = pcmreadcallback;
result = system_->createStream("./1.mp3", FMOD_LOOP_NORMAL | FMOD_SOFTWARE | FMOD_OPENUSER | FMOD_CREATESTREAM, &exinfo2, &sound2_);
ERRCHECK(result);
result = system_->playSound(FMOD_CHANNEL_FREE,sound2_,false,0);
Basically, 1 channel, 32-bit floating point PCM data. This is set on both the iOS and windows playback programs.
Now, on iOS, I set the AVAssetReaderAudioMixOutput audio settings like this:
NSDictionary *audioSetting = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithFloat:44100.0],AVSampleRateKey,
[NSNumber numberWithInt:1],AVNumberOfChannelsKey, //how many channels has original?
[NSNumber numberWithInt:32],AVLinearPCMBitDepthKey, //was 16
[NSNumber numberWithInt:kAudioFormatLinearPCM], AVFormatIDKey,
[NSNumber numberWithBool:YES], AVLinearPCMIsFloatKey, //was NO
[NSNumber numberWithBool:0], AVLinearPCMIsBigEndianKey,
[NSNumber numberWithBool:NO], AVLinearPCMIsNonInterleaved,
[NSData data], AVChannelLayoutKey, nil];
I set the PCMIsFloatKey to 1 so that the PCM data is a floating point, I set the bit-depth to 32, 1 channel, so that everything matches the FMOD output settings.
I read the data and write it into a circular buffer:
float* convertedBuffer = (float * ) audioBufferList.mBuffers[0].mData;
//We don't need the audioconverter on iOS
//Fill up the circular buffer
for(int i = 0; i < numSamples; i++)
{
circularAudioBuffer_[bufferWritePosition_] = convertedBuffer[i];
bufferWritePosition_++;
if(bufferWritePosition_ >= circularBufferSize_)
bufferWritePosition_ = 0;
}
Then read the data from the buffer and write it into the audio stream in the pcmreadcallback:
float *writeBuffer = (float *)data;
for(int i = 0; i < dataLength; i++)
{
sampleBuffer[i] = circularAudioBuffer_[bufferReadPosition_];
bufferReadPosition_++;
if(bufferReadPosition_ >= circularBufferSize_)
bufferReadPosition_ = 0;
}
With this, the audio plays perfectly, and the range of values inside the circular buffer is 0.0-1.0f
Now, on windows, I initialize the sound from which I read the data like this:
exinfo.cbsize = sizeof(FMOD_CREATESOUNDEXINFO);
exinfo.decodebuffersize = 44100;
exinfo.numchannels = 1;
exinfo.defaultfrequency = 44100;
exinfo.format = FMOD_SOUND_FORMAT_PCMFLOAT;
Setting the same parameters: 1channel, 32bit floating point. I read the data and write the data in the buffer:
FMOD_RESULT result = sound_->readData(rawBuffer, N4, &bytesRead);
float* floatBuffer = (float*) rawBuffer;
for(int j = 0; j < N; j++)
{
circularAudioBuffer_[bufferWritePosition_++] = floatBuffer[j];
if(bufferWritePosition_ >= circularBufferSize_)
bufferWritePosition_ = 0;
}
Now, when I read the data, I get very high or very low floating-point values (about 1e34 or -1e33). In the test program, I can't hear anything in the output.
I can switch the input and output sound format to PCM32 and it plays fine in the test program, but can`t be read properly in Unity3D (it screeches a lot, but I can make out the song).
Can anyone help me figure this out and make it works properly using the PCMFLOAT format? thanks!
TL;DR: I can't read data from FMOD sound with PCMFLOAT format!

Answer 1

From Fmod Support: Fmod Forums
The specified output format doesn't matter. The FMod codec will always return PCM16 and the iOS codec returns PCMFloats. So, I need to convert them:
(float)pcm16in[j] / 32768.0f;
In addition to this, I was (accidently) initializing the output stream with an MP3 file, which made it so that I couldn't change the output format.