High Sierra: iMovie won’t open AVCHD (.mts) files

Can’t open AVCHD (.MTS) files in iMovie on your Mac machine running macOS High Sierra? If so, you may wish to read this post. It explains a workaround to solve the issue via transcoding AVCHD (.mts) files to Apple InterMediate codec encoded MOV files.

iMovie no longer supports AVCHD video, how to fix?
“Hi all, I find it’s odd that iMovie no longer supports AVCHD video after updated to macOS High Sierra. I have to say every time iMovie is updated there is always something. If you know what I mean. In the past it has worked perfectly. Is there anything I can do to solve the issue? Please suggest a solution if you know. Thanks in advance.”

High Sierra: iMovie won’t open AVCHD (.mts) files
Before Apple releases a fix for the issue, currently, the only workaround I have found is to transcode the .MTS file to a .MOV file. HD Video Converter for Mac will be able to convert the format over to something iMovie can use. Here is a quick guide on how to encode AVCHD video to iMovie preferred AIC .mov video via using this converter app. Simply follow it to see if this solve the issue you are having.

How to convert AVCHD (.mts) files for iMovie editing on High Sierra?

Software requirement
HD Video Converter for Mac
mts to imovie converter for high sierra

Follow these steps:
1. Install and run HD Converter for Mac as a MTS Video to iMovie Converter on High Sierra. The main interface appears as below:
iMovie won’t import AVCHD MTS correctly on High Sierra

2. Click on ‘Add File’ to add your AVCHD MTS files to the program from your camcorder or from a card reader, or from an archived folder that contains your source media.

3. From the “Profile” menu, choose ‘Apple InterMediateCodec (AIC) (*.mov) as output format from ‘iMovie and Final Cut Express’ column.
iMovie won’t import AVCHD MTS correctly on High Sierra
Important: If you’ve loaded a number of video clips to do batch conversion, please do remember ticking off ‘Apply to All’ option before you start.

4. (Optional) Click ‘Settings’ button and go to ‘Profile Settings’ window to custom video and audio settings if necessary.

5. When ready, click ‘Convert’ to start transcoding mts files to AIC – the best suited editing format for use within Apple iMovie.

6. When the conversion process is complete, click ‘Open Folder’ button to get the generated AIC QuickTime files and open them in iMovie for further editing with optimal performance.

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