IINA saves a thumbnail strip for every video you scrub, and keeps them
IINA stores seek-bar thumbnails in ~/Library/Caches/com.colliderli.iina/thumb_cache and does not prune it. How to measure and clear it on a Mac.
When you hover over IINA's seek bar, it shows a preview image. To do that quickly it generates a strip of thumbnails for the whole video and saves it. Those files stay after you have finished watching, one set per video, in ~/Library/Caches/com.colliderli.iina/thumb_cache.
Users have reported the folder reaching hundreds of megabytes on a modest library, in issue 3179 on IINA's GitHub tracker. It grows with the number of different videos you open, not with how long you watch.
du -sh ~/Library/Caches/com.colliderli.iina ~/Library/Caches/com.colliderli.iina/thumb_cache 2>/dev/nullClear it
osascript -e 'quit app "IINA"'
rm -rf ~/Library/Caches/com.colliderli.iina/thumb_cacheIINA rebuilds a video's thumbnails the next time you open it. Your playback history and resume positions are kept elsewhere, so they are not affected. If you never use the preview, you can turn thumbnail previews off in IINA's settings, and the folder stops growing.
Related: Kodi thumbnails and the QuickLook thumbnail cache.
Common questions
Where is IINA's thumbnail cache?
In ~/Library/Caches/com.colliderli.iina/thumb_cache. Older versions kept it under Application Support; current ones use the Caches folder.
Is it safe to delete IINA's cache?
Yes, with IINA closed. Thumbnails are regenerated when you next open each video, and watch history is stored separately.
Does IINA clean its thumbnail cache by itself?
Users have reported it growing without being cleaned. Deleting thumb_cache now and then, or turning thumbnail previews off, keeps it in check.