Retrieve Youtube storyboards (closes #9868)

[MarcAbonce]

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Description of your pull request and other information

This PR adds 2 related options: --list-storyboards and --write-storyboards.
This allows users to list or download a YouTube video's storyboards. Storyboards are grids of those small images that appear when hovering the cursor over a video's timeline.
Issue #9868 gives more details on this feature. This PR should close that issue.

YouTube has multiple versions of the storyboard (specified in the url), which differ by size and by number of frames per image file. Usually, though, there's a default version which is a single 10x10 image, like this.

This options only support YouTube for now, but many video sharing websites have a similar feature, so support for those could be easily added afterwards.

[dstftw]

1. Add documentation in extractor/common.
2. Add storyboard meta field similar to thumbnail.

[MarcAbonce]

I just updated with the required fixes.

[MarcAbonce]

I updated with the requested changes.

The _write_thumbnails function needs to be called for both thumbnails and storyboards, though, in case a user wants to download both. So I can't see how would you completely avoid duplicating that call.

I also removed the unit tests I had added originally because I noticed that YouTube stopped returning the storyboards for a couple of days earlier this month, so it seems like we can't always rely on them being available. It looks like the extractor doesn't unit test for thumbnails either, so I hope this isn't a problem.

[johnyoonh]

Even if Youtube does not return the proper value. I think this option will be very helpful. @MarcAbonce I am interested in making changes.

[MarcAbonce]

@johnyoonh, sure, feel free to open an issue or a PR to my branch if you want to make changes for this pull request.

[johnyoonh]

@dstftw Is this PR not acceptable?

[MarcAbonce]

I just updated this PR with some fixes. Everything should be working correctly now.
If there's still anything that needs to be fixed, I'd appreciate any feedback.

[WinXaito]

Hello,

Where is this PR? I would be interested to have access to this feature.

Thank you

[MarcAbonce]

@WinXaito, right now you can pull the code from my repo and checkout the storyboards branch.

You can also install it with pip as git+git://github.com/MarcAbonce/youtube-dl.git@storyboards although the installation is really slow. Since this code is not merged yet, I occasionally update and rebase the branch. When that happens, you would have to force an update or just uninstall and reinstall again.

[tfabris]

@MarcAbonce @dstftw - If I'm reading this thread right, this code is not yet pulled into the main branch because we're waiting on a resolution of some questions about a code review, between you two kind folks. I think this has been sitting here for a while, though, like, over a year, correct? Seems a bit long to wait for a code review. 😃

Man, I'd really like this feature in the mainline. I know that I can do a pull of the code and build my own, but with my current use-case, having it in the mainline would be so much nicer!

What can we do to poke this farther along?

Thanks for working on this feature!

[MarcAbonce]

I rewrote my changes in the _write_thumbnails function to remove the code duplication problem and hopefully also make that part a little bit more straightforward. As far as I can tell, that was the only issue left from the code reviews.

[tfabris]

:)

[tfabris]

Hey @dstftw - Any word on approving this review?

[MarcAbonce]

For anyone that's still interested in this feature, while this repo was down I started working on a separate library to include this feature alone. Now it's available as thumbframes_dl in PyPI: https://pypi.org/project/thumbframes-dl and in GitHub: https://github.com/MarcAbonce/thumbframes_dl

I'm still keeping this PR open in case there's still some interest in ever adding this feature to youtube-dl.