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Module: LCKFMOD | Version: 1.0 | Platforms: All

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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.

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Supported Channels

ChannelSupportedDescription
GameYesFMOD Studio master bus output
MicrophoneNoUse LCKUnrealAudio or LCKOboe
VoiceChatNoUse LCKVivox

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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.

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Dependencies

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

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Automatic Integration

The plugin automatically:
  1. Detects FMOD Studio plugin presence
  2. Registers capture callback on the master bus
  3. Registers with the LCK audio system

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Source Implementation

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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;
};
MemberTypeDescription
CaptureDSPFMOD::DSP*Custom DSP node used for non-destructive audio interception
MasterGroupFMOD::ChannelGroup*Reference to the FMOD master channel group for DSP attachment

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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    │
                      └─────────────┘

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Technical Details

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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
});

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DSP Lifecycle

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

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Configuration

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Sample Rate

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

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Output Format

Set FMOD Output Format to Stereo. The default 5.1 surround is not supported at this time. FMOD output format
Voice chat and game audio must match in samplerate, otherwise audio distortion will occur in recordings.

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Performance

LCKFMOD has minimal performance impact:
MetricImpact
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.

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Compatibility

FMOD VersionStatus
2.02.xSupported
2.01.xSupported
2.00.xSupported

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Troubleshooting

  1. Verify FMOD Studio plugin is enabled
  2. Check that audio is playing through FMOD
  3. Verify master bus is not muted
  4. Check LogLCKFMOD for errors
  1. Check sample rate matches between FMOD and encoder
  2. Verify buffer sizes are adequate
  3. Check for CPU overload in FMOD profiler
  1. Verify FMOD system is fully initialized before capture starts
  2. Check that MasterGroup is valid
  3. Look for FMOD error codes in LogLCKFMOD

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Log Category

DECLARE_LOG_CATEGORY_EXTERN(LogLCKFMOD, Log, All);

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See Also

Audio Overview

Audio system architecture

Wwise

Alternative middleware integration