It happens with me. For the record, I’m on Windows. Don’t know if that makes any difference.
Another issue I am having is that the keyframes don’t work. Only the drag handles for the Simple Keyframes seem to work but the trim handles don’t work as when you click to another filter and back again they are reset to the default positions and the advanced filters don’t show up when the keyframes button is pressed.
Although Persistence is not bad it is a bit abstract. Perhaps a better name for this effect is Trails. 
I think motion blur implies this combined with some directional blur as well. While CSS blur() does not support direction, maybe it will help and can be added as a parameter that multiplies with the level.
Hope @Elusien won’t mind my mucking with his code… Fixed the advanced key frames issue.
webvfx_persistence.zip (4.8 KB)
Also added the filter to google drive.
Hey, I just took at look at your code and see you are directly accessing pixels. So, CSS blur() would not work. I also realized it is might the same as FFmpeg tmix, which is available in MLT as avfilter.tmix. It will be much faster in C and also uses slices. tmix/avfilter is not, however, keyframeable.
Yeah, that seems to work now. The trim handles in Simple Keyframes being reset if the clip is clicked away or deselected and reselected is still a problem though.
By the way, @Elusien, the same two problems that are affecting this Persistence filter (i.e. the trim handles defaulting after clicking away and the advanced keyframes not appearing) also seem to be affecting the latest version of your Sniper filter.
The sniper scope version that I have has no key frame problems.
Sniper_scope.zip (17.2 KB)
It’s also on google drive.
I’m not experiencing that issue.
Here is a demo that shows no advanced keyframes are showing up with the latest Sniper filter I got from both your google drive and Elusien’s page.
Here is a demo showing the trim handle reset problem with Persistance.
And here is a demo showing the same bug with Sniper. Also, note how after I first move the trim handle with the Sniper filter then move the playhead the values in the X and Y parameters are changed even though I don’t touch those.
I’m more than happy for you to fix any problems. Unfortunately, I got hold of a meta.qml file from an old version of a filter I have not made public and modified that for the “persistence” filter, forgetting that that one was wrong. I have now deleted it so it doesn’t happen again.
I may modify it to use a webgl shader and see how that affects the speed of the filter.
The trim handle bug affecting HTML based filters was brought up here.
Fixed the trim handle issue for Sniper scope and persistence.
webvfx_persistence.zip (4.8 KB) webvfx_sniper_scope.zip (17.2 KB)
The advanced key frame issue with sniper scope occurs when the filter is trimmed. The x and y positions are set to -100%. Workaround is to reset the x and y positions to default. Then the key frames will work.
Updated google drive.
Working well - quick and easy to apply.
Very quick demo - 2 segments with Persistence (persistense?) applied, both at the default 50%.
Thank you @elusien, great work, well done 
Cool!
Nice. 
The advanced keyframes on the Sniper filter are still buggy though. Apply the Sniper filter, activate advanced keyframes on either the X or Y parameters and put the mouse right on one of those value bars. Use the scroll wheel on the mouse to move the value of either X or Y to 85.50%. Then play the clip for a bit then pause it. Take now the mouse and put it over the percentage on the parameter to move the number in small increments. Scroll it either up or down. The cross hairs on the screen will disappear. Here is a demo.
Glad to see people having fun with the new filter.
I chose the name “persistence” correct spelling, rather than “motion blur” as it more accurately describes what it does. See Persistence of vision - Wikipedia for more information.
Hi @Elusien, just to let you know it is spelled in two different ways on your website. It comes up in Shotcut as “Persistense”.
Thanks for pointing that out. I have corrected the webpage.
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