game-audio-guide

Game Audio Plugin Implementation Guide

Steps apply to both Wwise and FMOD unless noted.

Step 1 — Choose middleware and plugin type

| Middleware | Effect plugin | Source plugin | Mixer plugin | |------------|--------------|---------------|--------------| | Wwise | IAkInPlaceEffectPlugin or IAkOutOfPlaceEffectPlugin | IAkSourcePlugin | IAkMixerEffectPlugin | | FMOD | FMOD_DSP_DESCRIPTION (process callback) | FMOD_DSP_DESCRIPTION (generatetone or read) | FMOD_DSP_DESCRIPTION on a bus |

• Effect plugins modify an existing signal in place or out of place.
• Source plugins generate audio from scratch (synthesisers, procedural audio).
• Mixer plugins operate on a mix bus and see the summed signal from all inputs.
• Confirm the plugin type before writing any code — changing it later requires reworking the descriptor and callback signatures.

Step 2 — Set up the plugin descriptor

Wwise:

• Declare an AkPluginInfo struct with your company ID, plugin ID, and plugin type.
• Implement GetPluginInfo() to return it from your plugin class.
• Provide a CreateXxx factory function and register it with AK::SoundEngine::RegisterPlugin.
• Implement a matching AkPluginParamBase subclass for parameter storage.

FMOD:

• Declare an FMOD_DSP_DESCRIPTION struct with name, version, channel counts, and all callback pointers.
• Fill FMOD_DSP_PARAMETER_DESC entries for every parameter the DSP exposes.
• Export a FMODGetDSPDescription() function (or pass the struct directly to FMOD::System::createDSP).
• Keep the description in static storage — FMOD holds a pointer to it for the lifetime of the DSP.

Step 3 — Implement the audio callback

Wwise (Execute):

• Read channel count and frame count from AkAudioBuffer at runtime — never hardcode.
• Use io_pBuffer->GetChannel(ch) to access per-channel float pointers.
• Allocate during Init with the AK::IAkPluginMemAlloc* allocator; never allocate inside Execute.
• Return early if uValidFrames == 0 to avoid processing silent tail unnecessarily.

FMOD (read or process):

• Use inchannels and outchannels from the callback signature — do not assume stereo.
• Allocate during create/reset with dsp_state->functions->alloc / free; never allocate inside read / process.
• Never block, lock, or perform I/O; FMOD calls this from a mixer thread with a hard deadline.
• Return FMOD_OK after producing valid output; return FMOD_ERR_DSP_SILENCE only when the DSP intentionally produces silence.

Step 4 — Handle parameters

Wwise RTPC binding:

• Declare parameter IDs as an enum in your plugin header.
• Implement SetParam on your AkPluginParamBase subclass to copy incoming values into your struct.
• Wwise copies the parameter struct before calling Execute — read from the struct, not from SetParam directly.
• Clamp every RTPC value to its valid range before feeding it to DSP computation.

FMOD parameter system:

• Define one FMOD_DSP_PARAMETER_DESC per parameter in your FMOD_DSP_DESCRIPTION.
• Implement setparameterfloat / getparameterfloat callbacks to read/write from your plugin state.
• Use a fixed enum for parameter indices and keep it in the same order as paramdesc; do not rely on magic numbers.
• Use FMOD_DSP_PARAMETER_DESC with FMOD_DSP_PARAMETER_TYPE_FLOAT and the appropriate float mapping (LINEAR, AUTO, or piecewise linear) so Studio renders controls correctly.

Step 5 — Register, test, and package

• Wwise: call AK::SoundEngine::RegisterPlugin during engine init before loading banks; ship a .dll/.so plus a .xml authoring descriptor.
• FMOD: pass the FMOD_DSP_DESCRIPTION to createDSP or load via loadPlugin; ship as .plugin.dll/.so.
• Unit-test with known input buffers outside the engine; cover channel counts 1, 2, and 6.
• Test bypass, all-zeros input, and extreme parameter values.
• Guard debug logging behind #ifndef AK_OPTIMIZED (Wwise) or equivalent release flag (FMOD).