Weird line on video

I know what you mean. The video border artifact comes and goes  as the browser window resizes, or as the video element is set to different sizes. Try the following. I've used it successfully to eliminate the aforementioned artifact. It seemed to work on yours as well.

const videos = document.querySelectorAll("video")
videos.forEach((vid)=> {vid.style.filter = "grayscale(0)"})

The idea is that by applying this CSS filter (which does nothing) to the video, the rendering is shifted to the GPU rather than the CPU. This alleviates whatever the issue is causing the artifact.

How exactly you apply this fix is up to you. I use this version as an On Timeline Start trigger on the Master Slide. It applies the adjustment to every visible video. If the video is not available when the script runs, it will not apply.

You may have to set up a trigger to apply it later if the video does not come into the timeline immediately. You can also apply it directly to a single video if desired, using a combination of the object() function and a query statement that identifies the video element you want.

This is related to the following post discussing an old video rending bug.

https://codepen.io/el-muerto/full/WNVzVwO