Audio syncing issues!!! Please help!!!!

I have filmed a live perfomance on a 650d 50FPS and a 5D Mark III 50FPS and recorded audio externally via my Zoom H4N.
When I place the 650D footage on the timeline and sync it to the audio it matches up fine. When I pull the 5D Mark III footage onto the timeline above the primary storyline to begin syncing it doesn't match up.
I sync the beginning up fine but t will suddenly become out of sync as I play almost as if the footage is faster (or slower) than the 650D footage both filmed at the same frame rate. I often have these problems when working with different cameras and trying to sync up.
Any help would be appreciated!
Thanks in advance

I can confirm that the 5D Mark III footage appears to be faster than the 650D footage.
I synced up the begnning of the videos but the 5D Mark III footage ends before the 650D footage. Very strange!

Can you see how the top video seems faster?

What is the audio sample rate of each of the thee clips?

Here is the info for both video clips

The only noticeable difference is frame rate difference one at 23.98 and the other at 25fps... not sure why it's saying there is a difference when BOTH cameras were filming at 50FPS

Try opening the clips in the QuickTime player and seeing what the inspector there says.

How certain are you about those frame rates?

OK, what is the audio sample rate of the audio clip you're sync'ing to?

Why not make a mulitcam clip?

Hmmm on closer inpection the rates do appear different...
Well that's strange and both cameras were filming at 50fps...
Is there any way to still sync these clips?

I've just done what Phillip suggested and made it a multicam clip... Thanks everyone, it worked. x

YAY! FCPX is great for multicam... I would use it anytime there is more than one camera, no matter what!

Actually I take that back... It's still out of sync even in multi clip!

I did a retime and made the slower clip 4% faster and that is the closest I could get to a sync, although it's still slightly out of sync over time. I can't understand how this has happened with both cameras filming at 50FPS soooo frustrating!

shutterhire wrote: I did a retime and made the slower clip 4% faster and that is the closest I could get to a sync, although it's still slightly out of sync over time. I can't understand how this has happened with both cameras filming at 50FPS soooo frustrating!

This is just a guess, but: If your material is really 50 fps from both cameras, but FCP thinks one is 23.98 and the other is 25 fps, in an effort to conform two differing frame rates it may somehow be causing the timing difference.

It is suspicious you report one clip is 4% faster -- that is the exact % difference between 23.98 and 25 fps. Of course each one should play back in the same real time, no matter what the frame rate -- provided the playback frame rate is the shooting frame rate.

But FCP believes there are two different media frame rates, so it can (1) Conform them by a rate stretch/shrink (2) Conform them by some other method like pulldown or motion interpolation, or (3) Do nothing. It may have done nothing.

I would suggest you inspect the actual characteristics of your media using an external tool like ExifTool: www.sno.phy.queensu.ca/~phil/exiftool/ or something else.

If both media sets really are 25 fps, then create a new project for 25 fps and import them.

Getting out of sync over time may be either an inexact rate stretch you did, or the camera timebases may be drifting. This is not unknown on extremely long takes like concert performances and lectures.