Greetings. I am currently working on an eight camera music concert video edit on Final Cut Pro and thought I'd share how exactly I get to a point where I can cut a multi-clip track from angle to angle, confident that my footage is in fact synched.
First, I load the footage. Once I have the ability to scrub through all the footage recorded, I pick a reference angle (usually for us it's a wide angle with the entire band in the frame). This is the angle I use for reference to synch the rest of the footage.
Next, I listen for a distinct sound: a guitar note being strummed or snare drum being hit. By scrubbing through the footage one frame at a time I can monitor my audio level and know when that sound occurs. From there I would mark that spot with an in point then go to the next camera angle and find that same sound in time by scrubbing through the footage just before it takes place and monitoring the audio level for it's peak.
Once I locate it, I drag the footage from that point to my timeline and set it at the in point we made earlier. However, just because the audio is perhaps in synch now does not mean the video is. Since audio waves travel it could reach the internal camera mics at different times. This goes for flashes of light from stage lighting and flash photography as well.
Now that I know the two angles are close to being in synch with each other I go to my reference angle and find a distinct motion point (usually a drummer hitting a tom or snare will suffice). I scrub one frame at a time, again, until I see the drumstick come in contact with a piece from the drum set. Once I find something I feel will work easily I mark another in point.
After that, I switch back to the angle I'm trying to synch with the reference angle and hopefully find the drummer at that same point in time. If the camera person captured it I just adjust the angle to move forward or backward the amount of frames it is off. If the camera operator did not capture it I have to find another distinct point from that angle and mark it with an in point so I can go back to the reference angle and count how many frames need to be moved. I always move the other angles to match the reference angle. Since our reference angle is a wide shot of the stage it will always include what the other cameras capture.
After I synch the two angles together I go to the next one and perform the same steps until all of the footage is synched and ready to be turned into a multiclip.
Voila! It is done. Thanks for taking the time to read this. Hopefully you will find it beneficial when synching different footage together.