Blackmagic Forum

Probably a stupid question, but I still have to ask it:
I have an HD timeline with 25fps and put a clip on it that was recorded with 100fps. So the slow motion should be played, but it does not. The question if I want to keep or change the different frame rates was answered with "I want to keep the timeline framerate". What am I doing wrong?
Thanks Benn

By default, it is going to play it time accurate. Right click on the clip and you can retime the entire clip, or use keyframes to speed up and slow down.

For that case simply change the playback speed to 25 in the "Clip Attribute" of that clip.

Thanks Uli, that's exactly what I was looking for!

bennjoell wrote:Thanks Uli, that's exactly what I was looking for!

Note that this works smoothly because your footage at 100fps is a multiple of your timeline 25fps. If you happen to shoot at, say, 60fps you may need to use optical flow to smooth out the playback.

Uli Plank wrote:For that case simply change the playback speed to 25 in the "Clip Attribute" of that clip.

+1

Uli is right.
Make the attribute clip change from 100 to 25 FPS in the media pool BUT BEFORE dropping the clip on the project TL at 25 FPS. After that it's too late.

(just change in clip attribute to see in the Metadata screen of the media pool as the duration changes ...). Test!

As long as we stay in the media pool, the image and the sound are in slow motion
If you go to the EDIT tab: activate 'Show All video Frame' and the image remains in slow motion but the sound is normal (+ the pitch)

No need for Optical Flow: Optical flow is used for the interpolation in the opposite direction: from 25 to 100 fps. It's more for : What does not exist and does "interpolate"

When frames exist at 100 fps: Just play them at 25 FPS ... without anything more.

60 fps to 25 fps would work just the same, but you'll have less of a slo-mo effect.
Only if a 4:1 ratio is needed 60 fps would require Optical Flow.

Jean Claude wrote:No need for Optical Flow: Optical flow is used for the interpolation in the opposite direction: from 25 to 100 fps. It's more for : What does not exist and does "interpolate"

Maybe I'm wrong, but I thought Optical Flow could also be used to smooth slow-mo playback when the two framerates are not even multiples of one another -- e.g., adding footage taken at 60fps to a 24fps or 23.98 fps timeline. I actually just did this with a project I'm working on and the motion seemed smoother with optical flow; it was very slightly jittery at first.

If you change the clip attributes to the timeline frame rate, there shouldn't be any jittering (other than perceived jittering from shorter exposure times).
But if you just throw a clip into the timeline and change the speed there, optical flow is needed for all frame rates that don't divide evenly.

Brad Hurley wrote:

Jean Claude wrote:No need for Optical Flow: Optical flow is used for the interpolation in the opposite direction: from 25 to 100 fps. It's more for : What does not exist and does "interpolate"

Maybe I'm wrong, but I thought Optical Flow could also be used to smooth slow-mo playback when the two framerates are not even multiples of one another -- e.g., adding footage taken at 60fps to a 24fps or 23.98 fps timeline. I actually just did this with a project I'm working on and the motion seemed smoother with optical flow; it was very slightly jittery at first.

In the case we are interested in: I would have rather used the "motion Blur" at the rigor but certainly not Optical Flow

Uli Plank wrote:If you change the clip attributes to the timeline frame rate, there shouldn't be any jittering (other than perceived jittering from shorter exposure times).
But if you just throw a clip into the timeline and change the speed there, optical flow is needed for all frame rates that don't divide evenly.

Ah that makes sense, and that's what I did (i used the retime controls, as I wanted to change the speed over the course of the clip). Didn't care about the sound as this clip will all be voiceover; I just deleted the camera-recorded audio.

OK, if you want to do ramping, the system needs to ‘invent’ new frames by some kind of interpolation. I second the suggestion to try ‘Blend’, it’s faster and may even look better.