randomize playlist order, i.e. --playlist-random

[glenn-slayden]

• I've verified and I assure that I'm running youtube-dl 2017.01.29
• At least skimmed through README and most notably FAQ and BUGS sections
• Searched the bugtracker for similar issues including closed ones

What is the purpose of your issue?

• Feature request (request for a new functionality)

Please add support for randomizing the playlist download order via --playlist-random (or whatever other switch name).

Since there is already an option for --reverse-playlist, I don't think this should be too hard? (I'd contribute it myself if I was more confident in my python skills.)

The motivation for this feature is that it could be used in conjunction with --max-downloads (i.e. set to a low value) to randomly "sample" a variety of videos from across a channel with lots of videos, as opposed to just being able to get the first few (or last few, using --reverse-playlist).

[glenn-slayden]

I should also add that the "random sampling" scenario I outlined above should be possible because you would be able to combine it with --download-archive to ensure that you don't get repeated videos in the random selection.

Here I'm referencing the fact youtube-dl already does the correct thing when you combine --download-archive with --max downloads N, namely, that you get the next "N" files that you haven't already downloaded--as opposed to "the N-or-fewer files out of the first N according to the selected playlist order." The latter could have been a perfectly valid interpretation—and could have been the implemented behavior—for the interaction between --max-downloads and --download-archive when both switches are present (but fortunately it isn't)

[ThomasChr]

New parameter added. Pull request created.

[ThomasChr]

Oh, I tested my code with '--max-downloads' and '--download-archive' - seems to work as intended!

[yan12125]

Thanks to @ThomasChr, there's --playlist-random now!

[glenn-slayden]

Very many thanks!