I messed up filming 1 camera was set to 25frame rate and the other 23.98.... how do I modify so the synchronise in multicam correctly. some of the rough cut edits seem to have worked but later I might find that the sound and voice has slipped... so can I do this to the event file and it will work on all the edits already rough cut multi camed.
FCPX can work with different frame rates in the same multicam. It uses the most numerous frame rate as the base for the multiclip and applies pulldown to the others. You shouldn't have a problem with slippage with your 25fps clip. However, it's obviously not best practices so tread carefully. If you convert your 25fps clip to 23.98 outside the program and then try to relink it to the original angle in the multiclip, you may get sync issues depending on whether FCPX thinks the file is still 25fps.