Avidemux 2.6 is under development as Jan mentioned, and it will change rapidly. It is one of the most complex programs I've encountered, which unfortunately makes it hard for non-technical people like yourself. The are three main problems that have stopped there being a binary file you can download and install: 1) the guy who used to do that, surfer, has gone afk for a while; 2) time; 3) The main developer named Mean does not have a Mac. Some people are good a tech stuff, other people are good at raising funds or finding used hardware. If you are the latter, I am certain that a used MacBook Pro would go a long way to getting us binaries again. Even if it took you a year, it would be all the difference. So that's just a thought. During that time, I will continue to learn more about packaging for Macs, but it's not a priority because 2.6 is not really ready for that.
You mentioned you have 2.5.4. The current version is 2.5.6, but there are a lot of important Apple fixes that will appear in 2.5.7. When that lands, I will try to bundle that up for people, but that is the old version that is essentially mothballed in favor of 2.6 due to it's design being mediocre for todays modern video formats (audio gets out of synch with video for example). Because 2.6 is the new great thing but it's only halfway finished, we are at a point where there isn't something bug free and 100% working for you. Most people have both 2.5.6+ and 2.6 installed, and they use the one that works for the job they are doing. Almost forgot to mention, there are 2.6 binaries available for Windows if you have a spare PC around. That might work for you.
Feel free to send Mean a private message if you'd like to donate.