WebM is an open royalty-free media file format designed for the web. The format is only for HTML 5 websites to stream videos online and few editors currently support dealing with this kind of files. iMovie in no exceptation. If you want to load downloaded WebM videos to iMovie for further editing the first thing is to convert WebM to iMovie patible video files. Since Apple InterMediate Codec(AIC) is the mostpatible codec introduced by Apple which ensures maximum editing quality and efficiency when working with iMovie themon practice for WebM to iMovie workflow is get a WebM to AIC Converter and transcode the .webm files to AIC MOV which will save you both time and trouble and all you need is to drag the result videos for prompt editing. Step 1 Run the WebM to iMovie converter on your Mac and then click the Add button to load the webm videos. You can also use the drag-and-drop method to load the media files to the application UI. Step 2 Click the Format box and select iMovie and Final Cut Express - Apple InterMediate Codec(AIC) (*.mov) as output format. The output videos will keep the original quality of WebM video and works well with iMovie 8 iMovie 9 iMovie 11 and iMovie HD etc. Tip Click the Settings icon to adjust video and audio parameters on the Profile Setting as you need to get the best quality video. Step 3 Click the Convert icon under the preview window and the Mac iMovie AIC Converter will start transcode WebM to AIC MOV for iMovie 8 on Mac.