Apple has updated its home video editing software iMovie, adding support for several highly anticipated new features. The main ones include the fact that iMovie canoneIt can handle 4K video. Unfortunately, this option is only available for Macs from 2011 and later with miniAt least 4GB of RAM. 4K video can be edited in true full resolution on all 5K iMacs.
In addition to 4K video, 60FPS 1080p video can now also be processed to make the "experience much more real". This option remains available to all Macs supported by the latest version of iMovie. In addition to supporting new video formats, the display of library content has also changed, which is now clearer and takes up less space for the video itself. The design has also changed more to the El Capitan style.
The option to import a work-in-progress project from an iPad, iPhone or iPod from iMovie 2.2 or higher has also been added. It is thus possible to start editing the trip editing already in the car on the way back and then finish the video on the Mac. But the content was also expanded. Apple added 10 new filters that you can use to edit your video.
*source: MacRumors

Great management, great app. Export 4k video, transitions, subtitles all in real time.
Well, toonehey, older versions of iMovie weren't this limited, nice that they brought back support.
You can also import older projects. You just have to upload them to iTunes. iPhone, open in iMovie, save again to iTunes, transfernest to the Mac and then you can open the project in iMovie on your desktop/laptop.