[Galene] Filtering outgoing video

[Juliusz Chroboczek <jch@irif.fr>]

Dear all,

One of my colleagues is using a pocket mirror in front of her laptop's
webcam in order to stream her (physical) desktop.  Teaching during
lockdown when you've got no blackboard at home is *hard*.

Obviously, if you use a mirror, then your writing comes out mirrored, so
you need to mirror it again before sending it out.  She's been using some
proprietary webcam software to do that, so I've just added the ability to
filter the outgoing video through an arbitrary Javascript function.

There's no user interface yet.  At the chat prompt, type

  /set filter "mirror-h"

or

  /set filter "mirror-v"

*before* you hit Ready.  The video should come out mirrored.

Known limitation: the filtering is unconditionally done at 30fps rather
than being synchronised with the webcam's framerate.  If anyone knows how
to fix that, please let me know.

I'd be grateful if somebody competent at Javascript could check my code.

-- Juliusz