[Feature request] flag for downloading only new channel videos

[jarpoole]

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Description of your issue, suggested solution and other information

I am attempting to use youtube-dl to continually download the latest videos from various youtube channels. YouTube-dl will be run daily from cron. Some of the youtube channels I am downloading from have over 1000 videos. YouTube-dl provides an option to download only videos which match the current date ( --date now ) and a robust way to keep track of videos which have already been downloaded ( --download-archive FILE ). The problem is that youtube-dl checks every video it finds on a channel against the archive file to see if it has already been downloaded and against the date to see if it falls in the date range. This process can take hours on a channel like ytuser:LinusTechTips where there are over 4300 videos. To compound the problem, this check happens every time the program is run.

I think the solution is quite simple. YouTube-dl already appears to list videos in chronological order (correct me if this is false). A flag should therefor be provided which stops checking if older videos are in the date range once it encounters a video which is too old.

I have read the documentation thoroughly and cannot come up with a different way to efficiently download only the new videos from a youtube channel. For this reason I think the new feature is needed which would be useful for a lot of users.

[ealgase]

If you're just checking against a download archive, it doesn't actually have to download each video webpage. I have a ~8000 video channel downloaded, and after downloading all the channel pages (~2 minutes), all the videos are checked in under a minute.