I would like to add this clarification: This happens to about a tenth of the videos I try to edit, with both Videopad and VSDC. They are all mp4 files. They have all been downloaded with WinX youtube downloader. There are no problems with videos of other formats, just with some mp4 files, mostly recent songs. Also I must explain that I am a Belgian pensioner living in Bujumbura, Burundi, for most of the year; where I accompany my wife who works at the Belgian embassy here.
I'll try to follow the steps borate indicated to allow him to look at one of these files. As an example : Sabrina Carpenter - Espresso (Official Video).mp4. Maybe there's some kind of edit-protection on them. In VSDC the song plays hackled with continuous short interruptions and in Videopad as soon as imported, the file changes from video file to audio file.
I'll try to send this one to borate.
Bye, Ronny