I went to your URL & was presented with this:
Since the video is 15:18 duration, you obviously need to download the variant in the middle of the VDH menu, the one I've indicated with the arrow. The one at the top of the menu is only 1:42, obviously not something you want.
It downloaded fine for me. I'm using Windows 7 64-bit, Firefox 103.0.2 64-bit, licensed VDH 7.6.3a1 beta, CoApp 1.6.3. You should always include that sort of information in any proper problem report. The downloaded file played fine in VLC. I didn't sit & watch the whole thing, just sampled it at 1-minute intervals & it seemed to be fine, video & audio, right to the end. I have to say that this guy exhibits all the hallmarks of the classic snake oil salesman. I hope you're not taken in by him.
But this video is barely 15 minutes long. You said something about problems with longer videos. Let's have another example. And don't forget to include the rest of the information to make this a proper problem report.
Before you post again, I have to warn you about something. When you open the Reply all text entry box, you will be quoting in my entire post, including the image. You probably are unaware of that. But when you open the Reply all dialog, scroll it down. You'll see a ... marker. Click it. Google has stealth quoted my post in & you neither knew that would happen nor did you request it. If you don't remove all of that, the possibility exists that the Google bots will censor your post because you have only a line or two & the quoted material is so much longer. So once you've expanded the stealth quote, highlight it & delete it. This is something you should discipline yourself to do in ALL your posts in ANY thread in this forum. Make sure you are not adding to the bloat by unnecessarily including the stealth quote.