Newpipe has a full writeup on why, but TLDR give it a few days and they will repair it.
Okay, maybe you are referring to
https://old.reddit.com/r/NewPipe/comments/1dz8bjj/about_youtube_playback_errors_youtube_changed/
?
TLDR: We will work on a fix which should come in the next days.
I didnt link it because i read it the day prior and am having trouble finding it again. Will link when i reaquire it. Sonething about google testing anti bot stuff.
Cant find exact link i saw but there are dup requests on git where people mention the a/b platform bot testing thing.
YouTube making trageted breaking attacks to third party apps through the api.
YouTube introduced another way to try to stop things like newpipe working. Newpipe are working on a fix.
I found a workaround for this in the meanwhile, at least for downloading videos. Use Seal Video Downloaded from Fdroid, it is essentially a yt-dlp frontend for Android. Once downloaded, you can simply long hold the video on NewPipe and then share the link with the Seal app. This will allow you to quick download the video and watch it using a video player like MPV.
It's nice because you can even pass it custom command line flags like the sponsor block flag:
--sponsorblock-remove all
Until Newpipe fixes their issue, this has been a good workaround.
Website : https://newpipe.net
Blog : https://newpipe.net/blog/
Github : https://github.com/TeamNewPipe/NewPipe
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