action contigent on the completion of another

I am trying to set up some actions in Lectora. I have various short audio and video files. I place them in an action group and they play at the same time. How can I set up one action to be contigent to the finishing of another. I don't really want to use the "delay before action" timer due to some of my audience computers are ancient and I am affraid the actions will still get out of sync. Can ANYONE offer a suggestion? Thx.

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