RMS, VU and LUFS audio meters

Getting audio measurement

Audio loudness information is kept in M_AUDIO_LOUDNESS structure. To get this information, you should grab a frame from a source and get M_AV_PROPS structure from the frame object.

MPlatform

You can get a frame either with the ObjectFrameGet method or by using an OnFrame event:

MFrame myFrame;
mySourceObject.ObjectFrameGet(out myFrame);
M_AV_PROPS myProps;
myFrame.FrameAVPropsGet(out myProps);

or

((MPlaylistClass)m_pMAudio).OnFrame += new MAudioControl_OnFrame;

void MAudioControl_OnFrame(string bsChannelID, object pMFrame)
{
    M_AV_PROPS myProps;
    ((IMFrame)pMFrame).FrameAVPropsGet(out myProps);
}

MFormats

You can get a frame with the SourceFrameGet method or any similar

MFFrame myFrame;
mySource.SourceFrameGet(-1, out myFrame, "");
M_AV_PROPS myProps;
int audioSamples;
myFrame.MFAVPropsGet(out myProps, out audioSamples);

The M_AV_PROPS structure contains an ancData field, that is a M_ANC_DATA structure with input and output audio loudness information (audOriginal and audOutput fields). The M_AUDIO_LOUDNESS structure contains the lufs field of LUFS_METERS type where the data is stored.

LUFS_METERS structure

The structure which contains fields:

Make audio meters

By getting the audio loudness information using a timer or for each processed frame, you can build audio meters of different types (RMS, VU, LUFS meters).

In MFormats, you can use LUFS data to implement an audio normalization algorithm. In MPlatform, there is internal audio normalization option.

Enable LUFS measurement

LUFS meters are disabled by default. A calculation increases a time to process each frame to 2ms. If the feature is not necessary for your project, or you need better performance in frame processing (e.g., for 60 fps or higher, each millisecond is important), it is better to keep it disabled. To enable LUFS measurement, you should set "audio.lufs" property to "true" using the PropsSet method.

It works for all source objects in MPlatform (MFile, MPlaylist, MLive - use "object::audio.lufs" property) and MFormats (MFReader, MFLive - just "audio.lufs").

mySourceObject.PropsSet("object::audio.lufs", "true");

Additional features

It's possible to add the lufs only for required channels, for example, to avoid lufs calculating from Dolby-E channels(in the SDK, currently, we can't decode it).

Just change with the PropsSet method value of the "audio.lufs_channels" property.

m_objMFReader.PropsSet("audio.lufs_channels", "2,3");

If you change lufs dynamically after playback you should reset the lufs calculations with audio.lufs_state property.

m_objMFReader.PropsSet("audio.lufs_state", "reset");  

Recalculation of audio data

In some scenarios like filling a frame with audio data from a buffer, or like getting modified audio data after mixing of several frames, e.g. with MFOverlay method, you need to recalculate the M_AV_PROPS values to get correct results. To do so, you need to call MFAudioGain method in this way:

pFrame.MFAudioGain("recalc_vu_meters", 0.0, 0.0);

Overlay RMS on frame

You can add RMS to a frame using the SDK; to achieve this, change the overlay_rms parameter. The table below shows the parameters for customizing RMS: