New json key field to indicate if a video was originally live streamed

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Can you add a new key to the output json file (--dump-json) for youtube videos that indicates if the video was originally live streamed?

This information can be retrieved from the header above the description of the video.

For example:
https://youtu.be/C8OZPrfpJUs - "Streamed live on 17 Feb 2018"
https://youtu.be/8YH8oY7vOk0 - "Published on 26 Feb 2018"

Alternatively can be retrieved from the youtube search page results where it will say "Streamed 7 months ago", as opposed to just "7 months ago". This can be found just below the video title , to the right of where it also shows, channel name and view count.

There is already a key for is_live, so I'd maybe suggest labelling this one as was_live.

An example usage case for this field would be to delay a download of video that was streamed live, in order to give the channel sufficient time to trim the live-stream. i.e. Because youtube allows live-streams to be trimmed (or have cuts taken out), and the video will still retain the original video ID.

This means youtube-dl could have downloaded a recently streamed video, and then the channel trimmed that video, and if --download-archive was in use then the the final edited video would not be re-downloaded

Thanks