[Feature request] Add an option to enable "frag_keyframe" when downloading livestreams

[sebma]

Checklist

• I'm reporting a feature request
• I've verified that I'm running youtube-dl version 2020.03.08
• I've searched the bugtracker for similar feature requests including closed ones

Description

Hi,

Can add an option to enable frag_keyframe when downloading livestreams ?

So as one can check what he is actually downloading by viewing the part file without having to waste bandwidth reopening the same network URL in another application, which is precious is in case of DSL Internet connection.

Thank you for your comprehension.

[sebma]

@dstftw It's an ffmpeg option :

$ man ffmpeg-all | grep -A1 " frag_keyframe"
       -movflags frag_keyframe
           Start a new fragment at each video keyframe.

That's all I know :)

[sebma]

@dstftw It enables to play an mp4 file while it's being written.