How to import videos in mp4 format into imovie ?

iMovie accepts Mp4/AAC. The ACC stands for Advanced Audio Coding.

Try dragging your Mp4 vid clip into an iMovie project timeline and see if it works. If not,

use the free download, Handbrake, to convert the video to Mp4/AAC, that it will do by default.

-- Rich

iMovie 10.1.8 the latest version will import most MP4 clips. MP4 is just a wrapper and what's important is the audio encoding and video encoder. iMovie likes H-264 video and AAC audio. If your clip will open in Quicktime player it will usually import to iMovie with no issues. If it opens in Quicktime open the inspector window and you can see the specs of the clip including the video and audio encoders.