fn active_speaker(
source: &PublishedSourceDescriptor,
media_id: TransportMediaId,
diagnostics: &BTreeMap<TransportMediaId, ActiveSpeakerSourceDiagnostic>,
) -> Option<DiagnosticsActiveSpeaker>fn active_speaker(
source: &PublishedSourceDescriptor,
media_id: TransportMediaId,
diagnostics: &BTreeMap<TransportMediaId, ActiveSpeakerSourceDiagnostic>,
) -> Option<DiagnosticsActiveSpeaker>