somewhat related, i used a tool to extract embedded jpeg preview images from raw images. much faster than actually using software to process the raw files if you just need to quickly share, your camera already "developed" them :)

http://www.fsoft.it/ERawP/

exiftool apparently can extract these also:

exiftool -a -b -W %d%f_%t%-c.%s -preview:all dir

Extract all types of preview images (ThumbnailImage, PreviewImage, JpgFromRaw, etc.) from files in directory "dir", adding the tag name to the output preview image file names.

https://exiftool.org/exiftool_pod.html