feat(lib): add audio to partial movie files and section videos

[jeertmans]

Overview: What does this pull request change?

With this PR, audio is added when writing partial movies. Before, it was only added at the end, so partial movie files and section videos did not contain audio.

Motivation and Explanation: Why and how do your changes improve the library?

My main motivation is jeertmans/manim-slides#375, in line with what I mentioned in #3501 (@behackl).

Further Information and Comments

The current PR is still in draft for the following reasons:

• it only works is audio (self.add_sound) is added before the first animation, I need to understand why and how to fix this (zero-padding does not seem to work as the concat output does not contain any audio stream in this case);
• must add tests;
• [ ] check if we can avoid padding audio every time we write some partial movie; I think zero-padding is necessary, having possibly empty audio streams seems to be a problem;
• check if this works for various output formats, especially webm;
• and check if audio is correctly split between two or more video files (i.e., does the concatenated version sounds like the original audio?).

Idea: it might be interesting to rethink the add_sound function to, e.g., let the user pass an AudioSegment instead of a file. This would be very useful for truncating audio, for example. That could also be a separate PR.

Reviewer Checklist

• The PR title is descriptive enough for the changelog, and the PR is labeled correctly

[jeertmans]

Note: the commit history looks very weird, even though I rebased onto your main branch...

[chopan050]

Hello, and thanks for your contribution!

The current PR is still in draft for the following reasons:

Is it still a draft? (asking because of the failing tests) If so, please mark it as a draft, thanks!

[jeertmans]

Hello, and thanks for your contribution!

The current PR is still in draft for the following reasons:

Is it still a draft? (asking because of the failing tests) If so, please mark it as a draft, thanks!

Hello! Yes it is, I forgot to tick the « draft » box :)

[jeertmans]

@chopan050 This is now ready for reviewing! I haven't added any test yet, but not sure where / how to correctly test this. I have looked at the current test suite, and we don't have many tests for sound nor partial movie files.

Edit: it seems that adding audio alters the duration of the media (could be logic) but also the frame rate?? So some tests (based on video metadata) are failing...