Extract initRange so that we can play adaptive streams directly in a player

[mihaiav]

Checklist

• [x ] I'm reporting a feature request
• [x ] I've verified that I'm running youtube-dl version 2019.11.28
• [ x] I've searched the bugtracker for similar feature requests including closed ones

Description

I would like to play/stream the adaptive streams in a custom player without to process/ffmpeg the streams. In order to do that I need the initRange for each stream. This data seems available on the youtube.com page as it's used by the youtube player as well but unfortunately it's not returned by youtube-dl

e.g initRange\":{\"start\":\"0\",\"end\":\"265\"},\"indexRange\":{\"start\":\"266\",\"end\":\"1282\"}

[nickerlan]

Any updates on that?