Many thanks to Alex Karahalios, who read my moan here about not being able to do anything yet with the new HEIF/HEIC compressed image files in High Sierra. He has put together a shell script, wrapped in an Automator workflow, which uses the free command tools ffmpeg and writerapp, to convert JPEG images to HEIF/HEIC format. These are available here, as a Zip archive: convertToHEIF

Alex writes:
You run ffmpeg to generate a bitstream file and then writerapp to create the proper metadata HEIF file. I created a bash workflow and I can select a file in the Finder and then use the Services menu to convert the file. You need to have ffmpeg and writerapp, but how to build them is on their websites.
I updated the scripts. Main changes were to allow parallel/batch conversions (when multiple files selected) with Workflow Services script. Also used “crf 9” vs “crf 12” which generates larger files of about half the size of the original. I also placed writerapp and ffmpeg executables there.

Please note that these are unsupported – they were written by Alex as a demo, and I am extremely grateful to him for letting me post them here. I hope that you find them of interest and value, if only to be able to generate your own HEIF/HEIC files. I also believe that the conversion should work fine in macOS Sierra, although only High Sierra will be able to create previews of them, or view the converted images.

Thanks also to Albinoz, who has worked with Alex to improve his workflow, and make it easier to install. This also uses the official version of ffmpeg 3.4 static. All the binaries are in the Services package, so all you have to do to install it is double-click it.

This has now been updated to fix the previous bug: it should now handle all pixel dimensions, although odd values will be cropped by one pixel.

It is available here: convertToHEIF4

Thank you to both of you for producing this for us.