The problem here is that current Avidemux builds, generated on Mojave, were reported to be incompatible at least with El Capitan. The situation with older macOS versions is unknown, so please try and report back whether the latest nightly runs on Yosemite. If it doesn't, you are out of luck. Even compiling Avidemux from source may be out of reach as Homebrew dropped support for Yosemite a while ago.
As dosdan already explained, 24-bit PCM audio files are unsupported while false positives for AC3 (and AAC) are mostly fixed, but this requires that you use a recent build.