Hello
If any archer willing to setup a nightly built just use this PKGBUILD (http://pastebin.com/Ga0KP8cg)
To install, just download and save it in /tmp. After launch makepkg and once is done, run as root (or sudo) pacman -U avidemux........Sorry I can't remember the whole name, just press tab, for auto-completion.
NOTE default is for QT4 and plugins, GTK wouldn't work fine yet, but it can be modified on the PKGBUILD.
I'll update once new version will be available.