iMovie export quality

Create a new project and place in it a clip of known 4k resolution. That will set the project as 4k. Then you can delete the 4k clip and insert your 1080 clips. The 4k project setting will remain. That should give you a 4k export option. Whether it looks better to your eye than your original 1080 movie would be your call, of course. Generally speaking a 4k video that was originally recorded in 4k should be a bit sharper than a 1080 video. I don’t know whether there would be a significant difference in an upscale situation.

— Rich

— Rich

At heart, the quality of the video is set by the resolution of your camera when you're filming. Yes, 4K is higher resolution than 1080p, because it has 4 times as many pixels. But there are two things to think about:

1. If your camera didn't shoot in 4K to begin with, you don't magically get 4 times as many pixels by outputting it that way; the software interpolates and makes an estimate of what the "extra" pixels should be. So, better, kinda.
2. Where is this going to be shown, and on what equipment? If it's going to be shown only on an HD screen, you're back where you started. How many in your audience have 4K displays? Keep in mind that transferring the file over the internet will take from 2 to 4 times as long, for example, and use 4 times the disk space.

Having said that, if you shot in 4K to begin with, go for it.

Export the  movie as a File to your desktop and, when the export box pops up choose the highest resolution option that you have available, with Better Quality Compression and High Quality.   For example

There is a Best (pro res) setting, but I wouldn't use that.  It gives you a 4x larger file size and is mainly intended for professional style editing.  The human eye likely wouldn't even notice a quality difference unless one zoomed in on the pixels.  So I would stick with "High" for the Quality setting rather than Best (pro res). 

The Mp4/AAC movie that you will get with all settings other than Best  Quality (pro res) will be high quality and pretty much universally compatible with all platforms and devices. 

 You didn't mention what resolution your movie was recorded in.  If you try to export out at more than one level higher resolution usually the results are poor.  So, you can go from 720 to 1080, or 1080 to 4k, if you have those export options, but don't go from 720 to 4k, as that would be two levels higher.

-- Rich

You're welcome. Most laptops don't have 4K displays, so, it is acceptable. I use an HD projector and am very happy with the images, as you say, "acceptable". But then, I spent most of my life watching TV on a cathode-ray tube equivalent to 480p.

If you don't have an HDMI out on your Mac, get a Mini DisplayPort-to-HDMI cable or adapter and hook it up to your 4K display. That's when you, especially as a photographer, will tell the difference.

Never mentioned much is frame rate for video. To keep data sizes down, often an HD or 4K video is output at 24 frames per second. But when doing fast pans of video, or transitions, that's when the 60 frames per second rate shines...at a cost of over twice the data size. Thank heaven for terabyte SSDs!

You are very welcome. 😊

-- Rich