Final Cut Pro on Three 4k screens UPDATE! AKA dual display bug fix.

So I had a big back and fourth many moons ago with the top FCP help desk person, and over time, I found out a few truths. At the time, he told me that FCP only works on 2 screens, and at the time, my M1MAX only supported 2 screens, It supports four 4k screens, but that is besides the point. My problem was getting the viewer to work on the screen I wanted it to work on, when you want to break out the clip viewer into another screen that is. It would randomly pick a screen after reboot, it still does this, and when you go to AV output, the attempt would send the client screen back onto itself on the main screen I am working on. This has always done this for me for what ever reason, no idea why.

I found the fix, a work around if you will, but it fixes the dual screen bug in the AV output setting.

1. In FCP, set your playback settings to the AV monitor of choice, I have 3 screens so I choose the Samsung 4k 42inch display.

2. Then open settings, make sure it is in the other display not being used.

3. Select the Displays setting so you can see the set of displays you are working with.

4. In FCP, set to AV Output that is in the Window drop down menu, bug hits, nothing seems to happen bonk.

5. In the Displays setting, select output monitor then switch the resolution it is on then switch it back! Client display activated!

There is it, the A/V output now works as it should. No idea why this happens, but I got it to work, further more, remember that comment I made about the FCP Pro phone support helper who claimed FCP does not work on more than 2 monitors?

It now allows me to set one AV display, and then I can also use the other display as my clip viewer. Since all this happened several years ago, I've updated from an M1MAX MBP to and M3MAX MBP, both can handle 4 displays, I think the M3MAX can handle 6? I've upgraded the 2 on the bottom there to 5k Studio Displays, all of this is playing back a 4k source flawlessly, AND on Tahoe! That was my bad, but as a video editor, I'm finding that Tahoe still works fine, even with all the bugs I am encountering. My work flow has not been impeded yet.

Anyhoo, I wanted to send this update to anyone that might need it and that has a similar issue, and yes, I have done fresh installs of everything, so you can cross that out. For what ever reason, A/V output has never worked for me from the HDMI port or even a dock like the Caldigit TS4 which I am currently using the 8K dongle attachment through the DP connection.

At some point I am going to update the Samsung to an OLED client monitor, maybe that will solve something? My attempt to get a better looking BAM for my office maybe. Hopefully dear reader, you have found a solution in this writing, it was an epic journey, but it can now be laid to rest.

Posted on Jan 26, 2026 7:15 PM

Top-ranking reply

British31 Author

Level 1

26 points

Posted on Jan 28, 2026 2:02 PM

Ok kids, so I figured it out, SmartSound SonicFire-Pro was the culprit, I don't know why or how, only that it was the one holdover app from 2006 I was still using up till 2014 or so to generate music for some productions I was working on that no longer exist. I deleted that app and all the supporting files out of the system, and now A/V Output works as it should! Who knew?

@Joe Redifer, that is what A/V Output is designed to do, select a target screen and go full, no menu, just pure video play back, when it works, it works! And now it is working for me, d@#m that took way too long to figure out!

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20 replies

Jan 29, 2026 8:00 AM in response to FilipOfficial

FilipOfficial wrote:

Luis, I have a hard time understanding the aspect ratio rationale, FCP is perfectly happy to use any HDMI monitor as an AV Output regardless of the aspect ratio, my friend has a Huawei MateView 28" 3:2 monitor for example, and I've for the longest time used 21:9 monitors and FCP happily spits out 16:9 timelines to the AV Output to both of those. I just find it fascinating that Premiere Pro & DaVinci Resolve both allows you to use the built-in MBP monitor as the A/V Output, which makes sense considering it's the best display on my desk (and probably 90% of other user's too, the specs is insane!) so it's the perfect screen to use as the full-screen secondary viewer. But it must be really hard to code considering PP & DR can figure it out but not Apple, or maybe it's because I've only payed for a $5000 USD MacBook Pro, so I don't deserve the privilege of having the the A/V Output on a Apple XDR display unless I gave Apple an extra $5000 or so for the Pro Display XDR?

According to the Final Cut Pro user guide, you have to have a resolution of 4096x2160, 3840x2160, 1080p or 1080i in order to be able to use a display as AV output. Perhaps you did it by changing to resolution to one of these options? Or is the user guide wrong?

Jan 29, 2026 10:04 AM in response to Luis Sequeira1

My monitor is 3440x1440p and have been selected as the AV Output, I can’t speak for my friends 3:2 monitor but I don’t think he has artificially limited his resolution considering I haven’t needed to do so. Either it’s a bug (a good one in this case!) or the manual is wrong. I haven’t tried this on FCP 12 though, so I can’t speak for the latest version. But no matter the outcome, I’ll continue sending feedback about this via the FCP feedback form to Apple, hopefully one day they’ll just let me choose whatever screen I want as the AV ”Output”, the MacBook’s built-in screens would be great for this purpose.

BenB

Level 6

13,240 points

Jan 28, 2026 4:03 PM in response to British31

Yes, A/V Output is exactly what it did in legacy FCP. It's your Viewer monitor, basically. No menus, just your Viewer (what we used to call the Canvas) output.

British31 Author

Level 1

26 points

Jan 28, 2026 5:23 PM in response to FilipOfficial

Not wrong!

British31 Author

Level 1

26 points

Jan 29, 2026 8:27 AM in response to British31

AND just like that, now it's working again, I give up!!!!!@

Final Cut Pro on Three 4k screens UPDATE! AKA dual display bug fix.