Hello!
I don't know if this is a problem only with the Internet Download Manager, but anyway...
In Avidemux, I can't cut YouTube VP9 videos that were downloaded with the latest version of IDM. The time slider doesn't work with them and with the keyframe editing I get the error message "Cannot go to next keyframe".
I'm using Avidemux 2.7.8, because 2.8.0 couldn't even open these video files...
Here's an example video:
https://www.youtube.com/watch?v=SSbBvKaM6sk
The videos work fine if they have been downloaded with ChrisPC Free VideoTube Downloader (it uses WebM container as opposed to IDM's MKV). But my antivirus software gives malware warnings about ChrisPC, so I'd rather not use it...
Please see https://avidemux.org/smif/index.php/topic,19868.0.html