I'm trying to descelerate a clip with the "speed/duration" menu.
To avoid quality issue, i selected "optical flow" and "Rendering from entry to exit"
The quality of the "primary file" is mp4 and not perfect, but still, with 65% descelerate (and renddering), the quality is very bad (as you can see my attached file)...
I really want to descelerate the speed withtout having these kind of visuels "bugs". i tried multiple export but apparently it's not a question of export...
What can i do?
You could try with a higher or lower percentage of deceleration so that the render is renewed than the one foreseen in the timeline and then you try to export again.
With an .MP4 file, anything can happen as there are a lot of factors that could be affecting the smoothness of your slowdown, MP4 is a file that is already "destroyed" by the enormous compression it requires to be able to look good without so much deterioration visually, but internally it is almost useless. With these types of files it is sometimes a matter of luck but if you dedicate yourself to making videos, I would suggest using files that are suitable for multigeneration (with less compression).
Thanks for th answer.
Yeah i know about mp4... sadly no choice...
I arleady tried a lot of time to "renew my slowdown with differents percentage,
If you look at my video, is not a question of smoothness issue, but like "broken pixel in the shadow"...
Anyway, i will try one more time tommorow, thank you a lot for advices Byron!
Of course that's what I mean, there are a couple of stunted frames. Try it when you have a time.
I lowered the percentage a little bit and the result is much better. Thanks a lot for the tip Byron!
Optical flow is great, except when it's not. In your case one of the problems is you are slowing an existing video with a cut in it (from the wide to tight shot) with optical flow. When you apply optical flow to a cut it will attempt to morph the pixels from the end of one shot to the first frame of the next shot ... and distort the image. The trick here is to trim out a frame or two from either side of the existing cut. This way you will remove the distortion between the shots.
The other problem (in your 2nd shot) is optical flow is attempting to track the pixels in the shadow of the hand - and failing. Optical flow is not good with subtle slow moving low contrast image changes ... like a soft shadow. Again it 's failing to accurately track these pixels. As you have found from Byron's suggestions - changing the speed can fix some of these issues. An alternative is to switch to 'frame blending' for just the shot(s) that are problematic with optical flow.
Another albeit complex solution is to duplicate your video layer (onto video track 2), with the duplicate using frame blending and mask this layer to hide the problems with the optically flowed layer - this only really works if the camera is not moving. This takes a lot of extra time and effort but works well. And if you know After Effects it's much easier to do these sorts of 'fixes' in AE.
... I should add, while I think optical flow in Premiere Pro is a life saver and usually pretty good - there are other options. You could try Time Warp in After Effects. It may or not work better in this instance. And there are third party plugin solutions that are excellent, though again much more complex to use (Twixtor is good).
I'd only recommend third party solutions if you have a lot of slow motion to do!