Why can't I play AC3 audio?

Well it took me a while but I have now updated to 10.14.6. No change.

I have two drives, the original hard drive and an added SSD. I use the SSD as the startup drive and keep the HD as a backup bootable drive. I did a clean install of 10.14.6 onto the HD and an upgrade-in-place on the SSD.

The Quicktime problem is isolated to the system on the SSD. Quicktime plays AC3 content just fine when booted from the HD. I attempted to use the QT app on the HD while booted from the SSD but that did not fix anything.

So what is QT looking for that's on my HD but not on the SSD startup drive?

No joy. As I said, AC3 will not play in QT. There are a number of test files available at thedigitaltheater dolby trailers site. I used several of them to verify my problem. All play fine in other players such as VLC.

There's no question that my Mac should play such files in QT. The mystery is why it won't.

It's the late 2011, aka MacBookPro8,2. Mojave was installed with the help of the dosdude Mojave patcher.

My video card failed a while ago - too late to get it fixed free by Apple. It's a well-known flaw in this model. Dosdude also provided a fix to ensure all video is constrained to the Intel graphics. Works great except you can't dim the screen anymore. Better than a bricked laptop, though.

Downloading the updater now - thanks for the tip. System Preferences only nags me to upgrade to Catalina but I'm not yet ready to abandon 32-bit completely. It never mentions any updates to Mojave.

[corrections to first post]

Macbook Pro late 2011

Mojave 10.14.5

QT 10.5

It'll be faster still to just ignore the problem. I use VLC for almost everything anyway. I think I'll let it go.

Getting my backup boot drive up to date was needed and worth it. But heavy lifting to make QT work for one old codec just isn't worth it. I don't like giving up but it's the rational thing to do.