plugins.youtube: rewind support / DASH streams

Feature Request

• This is a feature request and I have read the contribution guidelines.

Description

Youtube and some other sites have replaced HLS rewinding with DASH, and so Streamlink can no longer download live streams from the beginning.

Expected / Actual behavior

Some youtube streams have “rewind” enabled, allowing users to rewind to the beginning of the stream and watch the full stream with history.

Formerly, Streamlink was able to interface this and download the complete stream using --hls-live-restart. Apparently, youtube no longer uses hls for this, and so the ability to interface with dash and recover previous segments is required to ensure continued functionality.

Additional comments, screenshots, etc.

See related issues:

https://github.com/streamlink/streamlink/issues/2572 https://github.com/streamlink/streamlink/issues/2890 https://github.com/streamlink/streamlink/issues/2891 https://github.com/streamlink/streamlink/issues/2935

And especially these comments:

https://github.com/streamlink/streamlink/issues/2891#issuecomment-612662516 https://github.com/streamlink/streamlink/issues/2935#issuecomment-619452446

[beardypig]

I think this will require some quite significant work on the way streams are downloaded to make it feasible. I started work on a redesign of that stuff and maybe it’s something we can look at for 2.0.0 - I will write up some design docs next week and create and issue to describe what I’m thinking.

[ghost]

For people who need this functionality - there is an “alternative”, Mediahuman youtube-downloader, which does download youtube livestreams from the start. However for me a number of times it would cancel midway through the stream with “Download completed”. Another “alternative” would be setting up a cron job with some shitty bash script to get new livestream from rss and start downloading it as it goes live.