Hi Mickael,
Thanks for your patience here. Inputs on meta sounds are supported on Sequencer, but not for wave inputs.
A potential workaround would be to have an array of wave sources in your meta sound and use an integer to select an entry from that array. You could also create a blueprint wrapper around your metasound with an audio component, and a Sound Wave variable that’s exposed to cinematics. You can create a setter function that calls “Set Wave Paramter” and Sequencer will call that function when animating the Sound Wave variable.
To extend the audio track to support more input types look at FAudioComponentInputEvaluationData in MovieSceneAudioSystem and the corresponding maps in UMovieSceneAudioSection.
Thanks,
Austin