Add a delay or proper detection of video streams for auto-toggle

[gentoo-root]

Follow-up to timrogers/litra-rs#84 (comment)

Some applications open /dev/video* devices briefly to query something, without even starting the video stream. Known examples:

1. Chromium does it when opening https://youtube.com/ (Firefox doesn't).
2. Telegram does it when switching between chats (the reason is unknown yet).
   Telegram opens camera devices /dev/video* every time I open or close a chat telegramdesktop/tdesktop#28733

Litra Glow blinks for a split second every time when that happens.

Therefore, it would be useful if litra-autotoggle could either:

• delay turning on the camera by 100 ms, or
• detect whether the actual video stream has started, rather than just detect an opened file
  (not sure that the latter is possible).

[timrogers]

I've noticed occasional flickers too, but I hadn't figured out what was causing it 👀

Are you running on Linux or macOS? They have very different backends for detecting camera usage.

[timrogers]

There is some interesting code here designed to solve this kind of problem: https://git.math.uzh.ch/thinlinc/tl-webcam/-/blob/B16753_monitor_active_readers/research/inotify-02.py. I think a delay is probably the most sensible way.

[gentoo-root]

Are you running on Linux or macOS?

Linux.

[timrogers]

I'd be open to a PR to add a delay ❤

I might implement it myself over Christmas if I have some time, but it's a bit of a pain to test for me because I use macOS.

[gentoo-root]

Sure, if I find some time for this, I'll send you a PR, it shouldn't be hard to implement, I just don't know when it happens 😅

[timrogers]

I just implemented a fix for a similar problem in macOS, using a delay, in #23. It's probably a good template for your own PR, if you're able to put it together and test it on Linux.