Originally posted by FullertonImages Slight threadjack here, but...
How exactly does trandscoding to another frame rate work? With 30 fps and 24 fps, really only 6 of the frames in a second should be the same and the rest would all be slightly different moments. So I would think that it obviouslt can reimagine what those other moments were like, so does it just drop 1 of of every 5 frames to make it 24? And is it much harder to transcode between 25fps and 30fps, or is it the same?
There's 3 ways to convert 30p to 24p. One method is to conform the 30p footage to 24p. This basically tells the player to play the entire 30p clip at 24 fps. All the frames are kept, but played at 24fps instead of 30fps. Because of the slower framerate, the duration of your clip will increase by 25%.
You described frame dropping, which is a second method of converting to 24p. In this method, various frames are removed from the clip. This method is not very CPU intensive. Your clip duration stays the same, but the motion may end up somewhat jerky depending on which frames get removed. The best case for going from 30 to 24p is to probably drop every 5th frame.
A third method of converting 30p to 24p is to do frame blending. In this method, various frames are blended into a single frame. Like in frame dropping, the duration of your clips will remain the same. Unlike frame dropping, frame blending will give much better transitions than frame dropping when the scene has lots of motion. However, this method is much more CPU intensive.
In regards to your other question, it's generally easier to go from a higher framerate to a lower framerate, as you're discarding data in this process. Going from a lower framerate to a higher framerate, such as 24p to 30p, is much harder, as the software needs to now interpolate your existing data to create frames that weren't there originally. This interpolation is much more CPU intensive than frame blending, as it requires complex algorithms to calculate the motion between frames to generate new frames. The smaller the gap between the existing and desired framerate, the better the interpolation will look; a 30p clip interpolated from 24p source will look better than a 60p version interpolated from the same source.
- Jason