Final Cut Pro X: Rate Conform

Wednesday, 16 December 2015

When working with video clips that have frame rates that are close to being a multiple of the timeline frame rate, but not quite, Final Cut Pro X sometimes speeds them up or slows them down.

When this happens, you will be able to see a section in the inspector showing that its frame rate has been conformed:

tip-fcpx-rate-conform

This shows that a clip that normally runs at 25 frames a second will be slowed down so that it plays at 23.976 frames per second. It's playback speed on the timeline will be 95.904%. This means one frame of the clip will be displayed for one frame of the timeline.

Here are the rate conforms that Final Cut Pro X does automatically: 

When you add a clip with this frame rate To a timeline with this frame rate It automatically  plays back at this frame rate Speed % of original duration
         
23.976 24p 24 99.90% 100.10%
23.976 25p/i 25 95.90% 104.27%
23.976 50p 25 95.90% 104.27%
24 23.98p 23.976 100.10% 99.90%
24 25p/i 25 96.00% 104.17%
24 50p 25 96.00% 104.17%
25 23.98p 23.976 104.27% 95.90%
25 24p 24 104.17% 96.00%
29.97 30p 30 99.90% 100.10%
30 29.97p/i 29.97 100.10% 99.90%
30 59.94p 29.97 100.10% 99.90%
50 23.98p 47.952 104.27% 95.90%
50 48p 48 104.17% 96.00%
59.94 60p 60 99.90% 100.10%
60 29.97p/i 59.94 100.10% 99.90%
60 59.94p 59.94 100.10% 99.90%

This is a full listing of the combinations where Final Cut Pro automatically changes the speed of a clip. For any other frame rate combnations Final Cut will drop or repeat frames so that they source clip seems to play at its original speed.

For example if you add a 30p iPhone video to a 25p timeline, Final Cut will skip some of those frames every second so the playback speed remains the same and the duration stays the same: a 3 second 30p clip will take 3 seconds to display in a 25p timeline. If that same 30p clip was added to a 48p timeline, then Final Cut will repeat some frames so the playback speed will remain the same: the 3 second 30p clip will display for 3 seconds on a 48p timeline.