MKV video thumbnails in Windows Explorer

SageThumbs 2K shows a frame from each MKV video as its thumbnail in File Explorer. It reads only the keyframe it needs, and decodes 10-bit H.264, the usual format of anime encodes, which Windows cannot.

A frame from an MKV video of a beach, shown as a thumbnail

What you see

The frame is taken 30% of the way in by default, past any intro. Change that in Settings ▸ Appearance.
SageThumbs reads the file's own index to fetch the single keyframe nearest that point, a few megabytes, never the whole movie.
Common codecs are decoded by Windows' own Media Foundation codecs, and rotation flags are honoured, so a video rotated without re-encoding shows upright.

Limits

HEVC and AV1 video need Microsoft's Store extensions; without them Windows cannot decode the frame. st2k doctor names the one to install.
MPEG-2 video inside an MKV needs Microsoft's MPEG-2 Video Extension.
When no frame can be decoded, the file's embedded cover art is shown instead, if it has any.
In OneDrive and other synced folders, files stored on the PC get thumbnails as anywhere else. Online-only files are left to the cloud app, since nothing is downloaded just to draw a thumbnail.

More you can do

Press Space to play the video in Quick preview, with seek, volume, speed and repeat. Playback uses Windows' own codecs, and the title bar says when one is missing, for example for DTS audio.
Save frame as image writes the frame you are paused on as a picture.

Extensions this covers

.mkv

See every format SageThumbs 2K supports or browse all format guides.

Get SageThumbs 2K

Install it with winget:

winget install LunarWerxs.SageThumbs2K

Or download the installer from GitHub and run it.

Download the installer

Windows 11 and 10, 64-bit, on x64 and Arm. The same page has a portable zip that needs no installing.

Free for personal use

Home, hobby and other non-commercial use is free: every format and every tool. A company, a shop or anyone doing paid work needs a business licence for each PC.

A business licence is US$49 per PC once, with 12 months of updates, or US$2.99 per PC a month. See business licence pricing

Thumbnails not showing?

Windows caches thumbnails, and a file it failed on once stays failed. In SageThumbs, Settings ▸ Advanced ▸ Rebuild thumbnail cache clears the cache and restarts Explorer.
Make sure File Explorer's "Always show icons, never thumbnails" option is off, and that the format is ticked in SageThumbs Settings ▸ File types.
Run st2k doctor in a terminal. It only reads, checks the whole chain, and prints a fix under anything that is wrong.