I tried several versions included this:
Avidemux2.6_r2016_10_08_ec4b6104532.dmg
Impossible to open the application Avidemux_2.6
Unless you build Avidemux on El Capitan from source yourself (no idea whether this works on El Capitan, you need Homebrew which officially requires at least High Sierra + Xcode command line tools, there are caveats due to older Qt version at least), no.
Trying out ancient versions is probably even less fun.