FMOD - LCK Documentation

Module: LCKFMOD | Version: 1.0 | Platforms: All

Overview

LCKFMOD provides integration with FMOD Studio, capturing game audio output for recording. This plugin hooks into the FMOD audio system to capture the final mixed output using a DSP node attached to the master channel group.

Supported Channels

Channel	Supported	Description
`Game`	Yes	FMOD Studio master bus output
`Microphone`	No	Use LCKUnrealAudio or LCKOboe
`VoiceChat`	No	Use LCKVivox

Requirements

LCKFMOD requires the FMODStudio plugin which must be downloaded separately from fmod.com. The LCKFMOD plugin is disabled by default and will not compile without FMODStudio installed.

FMODStudio plugin for Unreal Engine
FMOD Studio project configured in your game

Dependencies

// Add to your .Build.cs
PublicDependencyModuleNames.AddRange(new string[] {
    "LCKFMOD",
    "LCKAudio",
    "FMODStudio"
});

Automatic Integration

The plugin automatically:

Detects FMOD Studio plugin presence
Registers capture callback on the master bus
Registers with the LCK audio system

Source Implementation

FLCKFMODSource

The core audio source class that captures game audio from the FMOD master channel group:

class FLCKFMODSource : public ILCKAudioSource
{
public:
    FLCKFMODSource();

    bool StartCapture() noexcept override;
    bool StartCapture(TLCKAudioChannelsMask Channels) noexcept override;
    void StopCapture() noexcept override;
    const FString& GetSourceName() const noexcept override;
    float GetVolume() const noexcept override;

    int32 Samplerate = 48000;

private:
    FMOD::DSP* CaptureDSP = nullptr;
    FMOD::ChannelGroup* MasterGroup = nullptr;
};

Member	Type	Description
`CaptureDSP`	`FMOD::DSP*`	Custom DSP node used for non-destructive audio interception
`MasterGroup`	`FMOD::ChannelGroup*`	Reference to the FMOD master channel group for DSP attachment

Capture Point

LCKFMOD captures audio from the FMOD master bus after all mixing and effects processing:

┌─────────────────────────────────────────┐
│          FMOD Studio System             │
├─────────────────────────────────────────┤
│  Events → Mixer → Effects → Master Bus  │
│                              ↓          │
│            DSP Tail Position (Capture)  │
└────────────────────────────┬────────────┘
                             │
                      ┌──────▼──────┐
                      │  LCKFMOD    │
                      │  Capture    │
                      └─────────────┘

Technical Details

DSP-Based Capture

The plugin uses FMOD’s DSP system to intercept audio non-destructively:

A custom FMOD::DSP is created and attached at FMOD_CHANNELCONTROL_DSP_TAIL position on the master FMOD::ChannelGroup
The DSP callback reads audio data without modifying the output
Audio callback runs on the FMOD audio thread
Data is marshaled to the game thread via AsyncTask
PCM format: 32-bit float, interleaved

// Audio data callback (simplified)
FMODSource->OnAudioDataDelegate.BindLambda([](
    TArrayView<const float> PCM,
    int32 Channels,
    int32 SampleRate,
    ELCKAudioChannel SourceChannel)
{
    // PCM is interleaved float data
    // Callback runs on game thread after async marshaling
});

DSP Lifecycle

StartCapture — Creates a custom DSP, obtains the master ChannelGroup, and adds the DSP at tail position
Audio callback — The DSP read callback copies PCM data and fires OnAudioDataDelegate
StopCapture — Removes the DSP from the channel group and releases it

Configuration

Sample Rate

We recommend setting the sample rate explicitly to 48kHz rather than leaving it at 0 (auto):

Output Format

Set FMOD Output Format to Stereo. The default 5.1 surround is not supported at this time.

Voice chat and game audio must match in samplerate, otherwise audio distortion will occur in recordings.

Performance

LCKFMOD has minimal performance impact:

Metric	Impact
CPU	< 1% overhead
Memory	~2MB buffer
Latency	< 1 frame

FMOD’s audio processing is highly optimized. LCKFMOD adds negligible overhead to the existing audio pipeline.

Compatibility

FMOD Version	Status
2.02.x	Supported
2.01.x	Supported
2.00.x	Supported

Troubleshooting

No audio captured

Verify FMOD Studio plugin is enabled
Check that audio is playing through FMOD
Verify master bus is not muted
Check LogLCKFMOD for errors

Audio distortion

Check sample rate matches between FMOD and encoder
Verify buffer sizes are adequate
Check for CPU overload in FMOD profiler

DSP not attaching

Verify FMOD system is fully initialized before capture starts
Check that MasterGroup is valid
Look for FMOD error codes in LogLCKFMOD

Log Category

DECLARE_LOG_CATEGORY_EXTERN(LogLCKFMOD, Log, All);

Audio Overview

Audio system architecture

Wwise

Alternative middleware integration

​Overview

​Supported Channels

​Requirements

​Dependencies

​Automatic Integration

​Source Implementation

​FLCKFMODSource

​Capture Point

​Technical Details

​DSP-Based Capture

​DSP Lifecycle

​Configuration

​Sample Rate

​Output Format

​Performance

​Compatibility

​Troubleshooting

​Log Category

​See Also

Audio Overview

Wwise

Overview

Supported Channels

Requirements

Dependencies

Automatic Integration

Source Implementation

FLCKFMODSource

Capture Point

Technical Details

DSP-Based Capture

DSP Lifecycle

Configuration

Sample Rate

Output Format

Performance

Compatibility

Troubleshooting

Log Category

See Also