Difference between optical flow in the retiming vs rate conform?

Hi everyone,

I have noticed two places in FCP X to apply optical flow. One is the retiming tool when I slow down or speed up a clip, I can select video quality, optical flow. The other is within the video inspector on specific clips that are different from the frame rate of the project. 

What is the difference between these two? I put a 50FPS clip into a 30FPS timeline and used the Optical flow option in the video inspector (I did not touch the retiming tool). Does this do the same thing as say selecting "Automatic" speed and then using optical flow within the retiming tool? or is it doing something else? 

Thanks!

Choosing Automatic Speed on your 50fps clip in your 30fps timeline will slow the 50fps clip so that it runs at 30fps. All frames are used 1:1 with the timeline framerate and no frames are made up. Likewise if you have a 24fps clip and a 60fps (or whatever) timeline and choose Automatic Speed, the 24fps clip will now be really fast. Optical Flow does its best to make frames up when needed. You can use it on slow and fast motion clips (and yes it helps on fast motion clips), but what you are seeing in the inspector is for real time playback. Optical Flow will try to make it look less juddery... more like it was a real 30fps clip instead of a 50fps clip. Same goes if the clip has a lower framerate than the timeline. Optical Flow is often a great solution but keep in mind that it's not perfect for all types of footage. Be sure to check for weird visual artifacts after applying it. I've usually found that the less motion blur a clip tends to have, the more weird warping and artifact can result with optical flow. It does not like hard edges that move. God help you if you have crisp bicycle spokes shot with a high shutter speed to remove motion blur in your video.

Redifer wrote:

Choosing Automatic Speed on your 50fps clip in your 30fps timeline will slow the 50fps clip so that it runs at 30fps.

This is incorrect.  Applying Automatic Speed to a clip makes that clip use the originally shot frame rate regardless of the project frame rate.  In this case, the clip shot at 50fps would play at 50fps in the timeline.  Without choosing Automatic Speed for that clip, it would be conformed to the timeline frame rate, which in the example would be 30fps.

LOL. Have you ever actually used Automatic Speed? You can't play a 50fps clip in a 30fps timeline. If you just drop it in, it drops frames to playback at 30fps. If you select Automatic Speed the clip CONFORMS to the timeline framerate, and in this case the 50fps clip would play slower. Try it.

Yes, I have used it since it's inception many times and it works exactly as I have stated. You also just contradicted yourself in your last post - "if you just drop it in, it drops frames to playback at 30fps." - exactly correct, in other words just dropping the clip in conforms it's playback to the current timeline. When you select "Automatic Speed", it then plays in that 30 fps timeline unconformed, and at it's original recorded frame rate (50fps). Here is the Apple manual section that deals with automatic speed: support.apple.com/guide/final-cut-pro/ch...peed-ver40b00150/mac

Final Cut Pro does not support variable frame rate timelines. You cannot have a clip play back at 50fps inside of a 30fps timeline. I'm hoping you're just really confused and not really thinking that's what's happening. The clip WILL change speed.

Here you go, friend:

See? The clip is slowed so that every frame of the original clip is played at the timeline framerate 1:1, just like I described. It is not playing at its original frame rate. It cannot.

From the user manual;
"For example, suppose you shoot a scene at 120 fps and then add the shot to a 30 fps project. If you apply Automatic Speed to that clip, every frame in the original clip plays back at the project’s frame rate of 30 fps, so the action takes longer and a slow-motion effect is created. You can use this method to create high-quality speed effects, because every frame in the original clip is played back—no frames are skipped or duplicated."

So you're both saying the same thing, with different ways of wording it. Please, we get it now, we all understand what happens, all original frames play back, period, no further escalation of an Explanation-War is needed.

JoeEditor wrote:

no further escalation of an Explanation-War is needed.

I would hope not, not sure why he had an issue with what I said.

Thank you both for your responses and clarification. So, to clarify.. Optical flow under the retiming tool smooths out clips that have been sped up or slowed down from their original frame rate so that they play smoothly in the new fast or alow motion. But optical flow within the video inspector keeps the clip playing at the same speed as the other clips in the timeline and smooths that out if there is an FPS difference?

Yes sir!

They both do the same thing, OF is OF... done.