Why do some videos on YouTube show up as "ADP" and don't download properly then?

[DarkSummoner2]

I have a problem with the Video Download Helper that's bugging me for a while now and since it became a lot more frequent just now, I open a thread for this problem:

Sometimes, when I want to download a video, I don't get the proper download options. Instead, I get options that are marked with "ADP".
If I download with these options then, the downloaded file is useless and empty. What is causing this?
I am getting concerned by this, because it happened for two videos in a little more than 24 hours now..... And I always use the newest version, so being outdated is not the problem. Is this YouTube doing something with its site to prevent VDH from working?
This is the video I currently encounter the problem with:

https://www.youtube.com/watch?v=Dt15bygPCdo

[mig]

Video marked ADP are streamed by youtube as 2 separate streams: audio and video. You must install the VDH converter to handle this automatically. The add-on will download both streams then aggregate them to end up with a single file containing both audio and video. You must make sure to end to wait for the end of the whole operation (you can monitor it from the VDH panel) before trying to open  the file.

[DarkSummoner2]

That sounds good. But why does it sometimes happen more frequently and some times less frequently? Right now, I have it with another video, so it really seems it's doing this with every video all off a sudden.
Is YouTube switching to a new standard of streaming?

And about the converter, when I use it, I get an ugly watermark obscuring the video. Isn't there any way around this? Why do you add this watermark?

[mig]

I really cannot tell about YouTube streaming strategy. They are not kind enough to let me know about this :) But VDH tries to do its best to capture videos from a given page at a given time.

Video DownloadHelper has been around for 10 years and developing and maintaining this application is far more than a full time job. If this has been possible, this is because we get some revenues out of our work. Since we refuse to sell our users data like many other "free" apps do (and believe me, we receive weekly if not daily requests for this), we make a living out of selling a license which avoids the watermark in converted/aggregated videos.

[DarkSummoner2]

I see. Where can I find this license exactly and is it a lifetime license or do I have to pay every month?

[mig]

It is a lifetime license available from https://www.downloadhelper.net/convert

[oswarz]

I'm having exactly the same problem except ALL YouTube videos are only availabel as ADP .  If I try to download, the video is trunkated --1 minute of less.  This is not 2016 or 2017, this is 2020!  I have never had this problem before.  I don't need ADP, l just want the old functionality back!