Incompatibility between speaker diarization pipeline and Waveform preprocessor

[hbredin]

Seems to be a problem with Waveform preprocessor.
Nothing related to this PR.
Merging but will need to have a look at this.

Originally posted by @hbredin in #1617 (comment)

[hbredin]

Relevant: happens for AliMeeting (that contains 8-channel audio)

[stale]

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