Film Strip Stutter

[michaelcwelch]

Hi All,

Have an interesting problem and was wondering if anybody has an ideas for a possible solution. 

I have a film strip with stills attached to it, that move up in the video. When you look at the render on mobile there is a flicker. Does anybody have any suggestions to fix this? 

I know I have seen this problem before and can't quite pin point the solution. 

[Mylenium]

Enable motion blur, change the speed. This is the same issue commonly associated with "jittery scrolling credits" and you can find plenty of advice on this under this and similar search keywords. It's the old framerate vs. actual temporal sampling thing. That said, of course even if you fix it it may still look odd on a mobile device. Those things do all manner of weird things to conserve battery capacity and processing power like adaptive screen refresh and such. If you realyl want to be 100% certain, review your clips on a stationary computer.

Mylenium

[Rick Gerard]

The effect is called Judder. It is caused by the stroboscopic effect of frame rate in the footage and movement. The refresh rate of the display is also a factor. So is the scale of the playback. For perfect movement, the speed must be an even number of pixels per frame, with the video at 100%. Six pixels per frame is about the maximum easily readable speed for small type for HD video at 30 fps.

If you are in a PAL country with 50Hz power, the refresh rate of the displayed is usually 50Hz. If you are in an NTSC country, the refresh rate is usually 60Hz. 

Any other frame rates are a bit of a compromise, but a speed that is 20% of the frame rate is a good place to start for an HD comp. That's 6 pixels per second in NTSC land and 5 pixels per second for PAL land. If you are working in 4K, you can double that speed and still get a reasonable reading time, and the images won't be blurred. 

Scale and media player, and you could see some judder because of the interaction of frame rate and speed; motion blur will help. This is just one of the rules you need to follow if you want the best-looking animation. You even have to follow the rule. 

Here's an expression you can add to the Position Property:

t = time / thisComp.frameDuration;
[value[0], value[0] - t * 4];

That will give you an easily readable speed for a title roll. Change the multiplier to any other whole number to change the speed. Anything faster than 6 for an HD comp should probably have motion blur. Double the values for 4K comp.