QuickTime Audio - Muting and GetMovieAudioFrequencyLevels

Q:  QuickTime 7.2 seems to have changed the way GetMovieAudioFrequencyLevels behaves. Muting and Volume changes now attenuate the returned frequency levels. Was this intended?

A: Yes, this was an intentional change. As of QuickTime 7.2 any Movie Volume, Balance or Muting in the audio chain is applied before the spectral analyzer that provides data for the GetMovieAudioFrequencyLevels API.

This change was made in order to more accurately reflect the actual mixed Movie output when returning the requested frequency levels.

If your application has a requirement to see frequency metering while a Movie is muted, the legacy Media Handler MediaSetSoundEqualizerBands / MediaGetSoundEqualizerBandLevels API pair may be used. Additionally, if simple volume levels are sufficient (as opposed to a frequency spectrum), you can use the newer SetTrackAudioVolumeMeteringEnabled / GetTrackAudioVolumeLevels pair of APIs introduced in QuickTime 7.0.

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