What is the last version of MAC oS X which works with FCP7?

As reported in a 2013 strand, FCP7 rendered about 15% faster under 10.6.8 than under 10.8.3. So I stayed with Snow Leopard until now, when some hardware is needing Mountain Lion.

Clearly FCP7 "works" under Mountain Lion, but I see an ugly defect in playback in the canvas. The video is 1920x1080 50p ProRes422 and it contains very rapid intercutting. Random horizontal bands are appearing in the canvas, as if the graphic card can't keep up. Rendering the sequence didn't solve this. Likewise, exporting a .mov file and putting it back in the sequence didn't solve it. Running the video off a RAM disk didn't help. However, that same .mov file plays nicely in QuickTime 7.6 under 10.8.5, so this is just a problem with FCP7 under 10.8.5. Of course it plays nicely in FCP7 under 10.6.8.

I reinstalled FCP7 in 10.8.5 and was careful to make its preferences exactly the same as in 10.6.8. The FCP7 playback preferences were like so.
Relaxing them in the 10.8.5 installation didn't help. Are there other preferences to fiddle with? Somehow FCP7 under 10.8.5 doesn't access the hardware as well as FCP7 under 10.6.8 does.

The editor couldn't judge what her rapid intercutting looked like in FCP7 under 10.8.5 and has returned to using 10.6.8. While others of you have gotten to Mavericks and beyond with your FCP7, here we're stuck at Snow Leopard. Have you been critical about the playback quality in the canvas?

Dennis Couzin
Berlin, Germany

[Note added 28 Nov 2015: same bad playback in FCP7 under 10.9.5.]

As described in the just previous post, FCP7 has a ugly playback defect under OSX Mountain Lion which it does not have under OSX Snow Leopard. Independently, I had a controller card that was working poorly with OSX Snow Leopard and well with OSX Mountain Lion. So I tried OSX Lion, in between, for the one-quarter chance it would solve both problems. Hurrah!

Now I've tested FCP7 under Snow Leopard (10.6.8), Lion (10.7.5), Mountain Lion (10.8.5), and Mavericks (10.9.5). Each was a fresh FCS3 install into a freshly installed operating system. The FCP7 playback defect starts with Mountain Lion.

I saw the FCP7 playback defect with a fast edited 1920x1080 50p ProRes422. There is occasional breakup at horizontal lines on the 100% scaled Canvas. It looks like incomplete screen refreshes. FCP7 playback has this defect, while QuickTime doesn't.

I've uploaded 13 seconds of the acid clip -- here -- so others running FCP7 under Snow Leopard, Lion, Mountain Lion, or Mavericks can help confirm that the playback problem begins with Mountain Lion.

Dennis Couzin
Berlin, Germany

[Note added 4 January 2016: any 1920x1080 50p ProRes422 will display the same playback symptom as the "acid clip".]