Video feature recommendation for h264.mp4 displayed on 4K retina display

Hello iScreensaver Community,

I’m looking to create screen savers for iMacs18,2 with a retina display from h.264.mp4 files aiming for the best possible resolution. I have a couple of questions and hope they havent been asked before:
1.) Is it advisable to upscale the video to match the resolution of the retina 4K display?
2.) The source videos have varying low frame rates (4, 6, 10, and 16fps). Should I consider increasing the frames per second to a higher rate (e.g., 30fps), or does it not significantly impact the iScreensaver performance?
3.) What bitrate do you recommend?

Your insights and recommendations would be greatly appreciated. Thank you very much! SOBU

The iMac 18,2 machines are about 6 years old now, and did not have the most powerful CPU or GPUs. A big concern with your video playback would be iincreased heat and energy usage. H264 / MP4 is a good format, although the quality of encoders varies widely, and we’ve seen cases where a poorly-encoded video could use extra CPU for no reason. See iScreensaver : Encoding Video for Best results for details.


  • using your video as is, test it out on the iMac. You can run the test from within the Installer by using the Preview button which will allow you to monitor CPU and GPU using the Activity
  • if you see high CPU/GPU usage, take your original video into QuickTime Player and re-export it. (Or, if you have Apple’s Compressor app, you can use that)
  • encoding the video to increase the resolution (to 4K) or framerate (to 30fps) is not advised, as this won’t make it look any better, and will likely use more CPU and GPU.

Does this help?

Great, thank you very much for your fast reply and help. I will run some transcoding tests and check the CPU usage.

1 Like