[Feature] Add support for livestream downloading

[philklc]

Describe the feature

Better handling of livestream downloads, including the use of --wait-for-video and --live-from-start flag

Reason for adding

Currently, YTDLnis doesn't seem to handle livestreams well. Downloading a livestream seems stuck at 0:00 with no option to stop and take what's already downloaded. (I did not leave it running until the livestream ends)

There are streams on YouTube that might be long running and the user might only be interested in recording a partial segment of it, using yt-dlp as if using a screen recorder, running it for the duration of the parts the user want saved.

On the other hand, there are streamers on YouTube that private or delete the stream right after the stream ends. Yt-dlp by default downloads a livestream live from current time, but with the --live-from-start flag, allows the livestream to be downloaded from the very beginning even when the stream is still live. The use of --wait-for-video is also helpful for the inverse case, automatically waiting for the stream to start before downloading begins.

Example(s)

No response

Additional context

No response