Update Video Loading/Export to use imageio

[DN6]

What does this PR do?

This PR changes the video loading/export backends to imageio

imageio with ffmpeg loading and export allows videos to play on a larger number of platforms. It also appears less prone to codec issues than OpenCV.

Fixes # (issue)

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline?
• Did you read our philosophy doc (important for complex PRs)?
• Was this discussed/approved via a GitHub issue or the forum? Please add a link to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[yiyixuxu]

thanks!
do we also need to add to the BACKENDS_MAPPING here?

diffusers/src/diffusers/utils/import_utils.py

Line 578 in a57a7af

BACKENDS_MAPPING = OrderedDict(

[DN6]

@yiyixuxu This would "break" a few repos that rely on export_to_video though. Since they would now have to install a new dependency
https://github.com/search?q=%22from+diffusers.utils+import+export_to_video%22&type=code

[yiyixuxu]

@DN6
ohh maybe let's keep the old code then?
we use imageio if is_imageio_available, otherwise, we use the old code, throw a warning that it might not work, and ask them to install imageio