Choosing Correct Video Rate With Clips of Various FPS?

"Final deliverable" is where you intend to have your video displayed. I'll differ with Mr. Jordan's recommendation by saying: if you haven't been explicitly assigned a specific frame rate to use — USE 30! Don't worry about trying to figure out the majority of the clip frame rates.

The youtube video about conforming video in FCPX is ridiculous... (sorry). Anyone still using fractional frame rate projects are idi... um... out of touch. There is no longer any purpose whatsoever in using fractional frame rates. Analog television is dead as a doornail and has been for a decade. [Same can be said for interlacing...] The reasons to use fractional frame rates simply do not exist anymore and using them just creates a multitude of headaches (including synchronization issues and timecode "confusion" [timecode is not time]). FCPX is very adept at conforming all frame rates without optical flow.

YouTube will take about anything but they recommend 30fps. If YouTube is your destination, consider yourself assigned. You do not want to try to upload anything that might cause YouTube to re-encode your source video with their codecs.

As for audio: keep all your audio sources consistent (48kHz sampling rate or higher - constant bit rate [CBR] - typically WAV or AIF - not MP4!!)

You can use any of these frame rates if you want to but you can't or shouldn't just combine different frame rates willy nilly. If you are using nothing but stock footage you might, for instance, find a wonderful clip at 30fps and build a story around that. In that case you should probably stick with only footage done at 30fps and not drop any other footage in with different fps. You might find something at 25fps that you like and in that case you could also use any 50fps footage because you won't lose any frames when it is played since 50 is a multiple of 25. Well you would lose some but it would probably not be noticeable. If you have a project that is set at 30fps and put in some footage that is 50fps it will be forced to drop frames because each second has too many frames. Yes, you can use optical flow to try to make things better but as Apple says in one of their docs, "This setting usually provides the greatest reduction in visual stuttering and artifacts. " That is to say, reduction of stuttering, not necessarily elimination. If you're just doing some little home movie thing it's really not a big deal. It's your movie but depending on how long the clip is and how many times you are tossing in clips to a timeline that does not match the fps of the clips the results could vary from hardly noticeable to horrible. You goal should always be to match the timeline to the clip in terms of fps. If you do choose to add a clip to a timeline that doesn't match its' fps, use optical flow, then render the clip and view the results to see if they are acceptable. In your above example, if all the clips you listed were of equal length and desirability you would want to use a timeline of 25fps so all of those clips and the 50fps clips could be used without lost frames that would cause problems. If, however there was a 20minute clip you liked that was 29.97 and everything else were short additions it might be better to make a project at 29.97. Bottom line is your project can only end up at some chosen fps and whatever clips in that timeline that don't match it are potentially something of an issue in terms of how the lack of matching frame rates are dealt up by the attempt to "fake" them via optical flow which is never perfect. The more fast motion involved the worse the problem is. If your non-matching clip is a static shot of a sunset then it may be entirely fine with no problem but if it's a fencing match then you might have many very noticeable blips in the video even when using optical flow.

Don't be confused. It is NEVER better to resort to fractional frame rates. Analog TV officially ceased on June 12, 2009. Analog is the only reason to use fractional frame rates. If it doesn't exist anymore, why would you!

If you need to understand where fractional frame rates actually come from, watch this video: Why is TV 29.97 frames per second?

It's one of the best explanations I've seen (and it beats digging through various documentations for it which most people won't do anymore.)

Convention is a poor excuse.

D-word (this site is rated G+++)! Where were you when I had this question about 29.97 vs. 30 fps? I ended up using 29.97, as I thought I'd need to make a DVD or Blu-ray from it. Well, that didn't happen, and it doesn't even seem to matter for that. I thought it was safer to go with 29.97 anyway.

Well, I guess you just missed my post.

So in the future can I just run the resultant .mov file through Compressor to convert it to 30 fps, should the need arise? Seems to me, based on the Compressor "user guide", the only side effect would be that the music would run at 1.001x speed. Or would the need ever arise to begin with? (I'll use 30 fps henceforth.) TIA.

Whether I missed it may be dependent on when you asked it. I was involved in a lot of work the last year or so to make precision timed effects. I know how to make them for fractional frame rates but that's what got me started asking: why the H* am I doing this??? I could not come up with a logical reason. So I finally woke up and realized that using fractional frame rates is simply no longer a logical choice. My favorite part of the video I linked is NTSC: Not the smartest choice.

However, if you've already "baked" a video in 29.97, just leave it as it is. Once you complete a project, it's just "archive". Go forward, not backward!

I actually do not use Compressor and haven't since Final Cut Studio days, so I cannot tell you if Compressor is a worthwhile effort. I don't see where audio would go out of sync once it's part of the actual published video file... and it won't hurt to try.

Wow. Never heard of NTSC being described as "not the smartest choice". From decades ago I do recall it being called "never the same color".

Yes, it's "baked in". But FCP won't let you change the frame rate anyway, no?

Sounds like you have a good plan and a reasonable take on the situation.