So I’m quite new to FMOD. I’m working in a video encoder for a game, basically I send the frame buffer and audio buffer to my native dll which encodes it via ffmpeg. Now, I’m trying to get the audio buffer each “audio frame” and the way to do that as I understand it is by creating a custom DSP, attach it to the head (or just before) and copy the buffer over.

So here is my code (it’s c#):

Custom DSP:

public class FMOD_AudioRecodingDSP
    public static DSP_DESCRIPTION CreateDSPDesc(out FMOD_AudioRecodingDSP dspObj)
        dspObj = new FMOD_AudioRecodingDSP();
        var desc = new DSP_DESCRIPTION()
            name = "AudioExport".ToCharArray(),
            version = 1,
            numinputbuffers = 1,
            numoutputbuffers = 1,
            read = dspObj.ReadAudioData,

        return desc;

    public RESULT ReadAudioData(ref DSP_STATE dsp_state, IntPtr inbuffer, IntPtr outbuffer, uint length, int inchannels, ref int outchannels)

        outbuffer = inbuffer;
        outchannels = inchannels;

        return RESULT.OK;

My “add DSP” code:

FMOD.ChannelGroup master;
lowlevelSystem.getMasterChannelGroup(out master);
master.getDSP(0, out mixerHead);
mixerHead.setMeteringEnabled(false, true);

// Trying to get a custom DSP in to FMOD to record audio for video
uint dspHandle;
FMOD.DSP_DESCRIPTION dspDesc = FMOD_AudioRecodingDSP.CreateDSPDesc(out DSPObject);
res = lowlevelSystem.registerDSP(ref dspDesc, out dspHandle);
res = lowlevelSystem.createDSP(ref dspDesc, out AudioRecordingDSP);

// Try 1
//res = master.addDSP(0, AudioRecordingDSP);

// Try 2
FMOD.DSP limiterDSP;
res = master.getDSP(1, out limiterDSP);

FMOD.DSPConnection conType;
res = AudioRecordingDSP.addInput(limiterDSP, out conType, FMOD.DSPCONNECTION_TYPE.SIDECHAIN);

res = AudioRecordingDSP.setActive(true);
res = AudioRecordingDSP.setBypass(false);

You can se my “Try 1” and “Try 2″… When I use “Try 1” I get it to call my DSP for a few times at startup, then it it stops calling it.
With “Try 2” my DSP never gets called…

So what am I missing?

Thanks In Advance!!

  • Cameron Baron

    Your code works fine for me.
    Are you getting any warnings/errors?
    The functions at the start of your “add DSP code” all return a FMOD.RESULT, they may be able to shed some light.

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Best Answer

I figured it out. I creates an instance of FMOD_AudioRecodingDSP in managed memory and sent it over to FMOD, and then… well I did not keep a reference to the object, so the instance got removed and so got the function instance.

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