The audio clips must have the same channel
type and each clip must be on a different track. If clips are already
linked, such as an audio clip linked to a video clip, they must
be unlinked before you can create a multi‑clip link.
If necessary, select the linked video and audio
clips, and choose Clip > Unlink.
Do one of the following:
Shift‑click to select a video clip and
more than one audio clip on separate tracks in the Timeline panel.
Shift‑click to select more than one audio clip on
separate tracks in the Timeline panel.
All audio clips must have the same track format (mono,
stereo, or 5.1 surround).