When I sampled it earlier it was doing a bunch of stuff in VideoToolbox. I’ll check again when I get home this evening.

Thanks. Sounds like we might have failed to open the hardware encoder and fell back to software encoding for some reason. I’m going to try to get some time on an iMac tomorrow and see if I can recreate the problem.

Ok I took a sample. https://gist.github.com/kballard/636fa3f6c09d6fc6e2a2a1efa33...

I also checked the Console. Here's what I found:

  default	19:55:42.767418 -0800	RetroClip	GVA info: preferred scaler idx 1
  default	19:55:42.769327 -0800	RetroClip	AVD encoder error: kAVDPictureEncode CreateContext, unsupported resolution 5120 x 2880
  default	19:55:42.808188 -0800	RetroClip	Using metal device <BronzeMtlDevice: 0x7f80bf037200>
                                                            name = AMD Radeon R9 M395X
  default	19:55:52.609993 -0800	RetroClip	LSExceptions shared instance invalidated for timeout.

My hero! Sounds like I should do some scaling for these 5k iMacs. I got away with up to 3840x2400 resolution just fine in my testing on various macbook pros, but I don't have any iMacs. I'm gonna go try one at the Apple Store tomorrow (not buy obviously, I'm way too cheap for that, but just use it for a minute).

EDIT: Yeah, I'm pretty sure 3840x2400 is the max supported by any recent Intel CPUs, and older ones are less. The iMac Pro might be a special case because I hear it uses its GPU for H.264 encoding. Anyway, querying what the max is for a given machine and then scaling to fit it was an easy fix. Hopefully I can get it deployed to the app store soon.

Finally just relaunched it again after the updates. it's now taking 10% CPU while watching a Twitch stream and 1–3% CPU when not. That's much better than 300% CPU :D

Glad to hear it! Not sure I need a 5120x2880 video anyway. I’d be perfectly happy with half that resolution.

I assume higher resolutions have a larger memory footprint. Is the RAM usage still reasonable at 3840x2400?