Flicker in Exported video with color grading filter

I’ve been using Shotcut 16.05 and recently 16.06. I had been using the color grading filter with no issues, and then for some reason, after a recent export, I get a flashing in the upper half of the video. It does this on all video with the color grading filter on. I stepped back to 16.05 to the same result.

I’m running Linux Mint 17.3 Cinamon with current updates.

To give an example here is a link to a video with the problem: https://youtu.be/XmD0jnSKQqA

Also, the problem seems muted or removed if I add another filter such as Brightness or Vignette.

Let me know if more information is needed.



Is GPU processing enabled?
Try exporting with parallel processing disabled.

GPU is not checked, but unchecking parallel processing seemed to do the trick. Thanks for the quick response.

OK, I have not been able to reproduce with a simple case of: open a clip, add the filter, make some adjustment, and export it. I also tried adding it to the timeline. And I tested with both progressive and interlace sources. It must be some combination of factors - perhaps other filters or scaling. If you figure out the combination, please let us know.

I will keep working with it and see if I can figure out the combination.

I went in and added a new track to the timeline and did an export with no filters and parallel processing checked. The footage exported fine. I left the presets.

I simply added color grading and made some modifications to the color wheels and exported with parallel processing on. The flicker was present. I exported with the color grading on without parallel processing and the flicker was not there.

To see if additional filters would have an impact, I added Contrast, Brighten, and Sharpen filters. After the export the flicker was not there even with the Color Grading and parallel processing on.

That’s as far as I have gotten with my testing. If you would like me to test other combinations, please let me know.

Did you use the same clip for both the original problem report and all tests? Maybe there is something between the combination of the Shotcut Video Mode and that clip’s properties that triggers the problem. There are thousands of factors and variables, and I cannot enumerate them all. You can reproduce it using Color Grading alone; I cannot, and I tested some combinations like I said.
I just uploaded a new v16.08.08 on the download page to address a couple of crash bugs. However, based on some observation I made while investigating this bug, I made some change to improve parallel processing in this filter (allow more of it). That change also made it into that version. You could test with that. Besides, you will want to upgrade to get the fixes.

I believe the initial issue was with the footage. I tried footage from another source and this did not happen. I was able to reproduce it without fail. After updating to your latest release, this issue is no longer there. I used the same footage that was previously used and was unable to reproduce the flicker.

Thanks for the help!