Free macOS plugin to play .mkv movies in Quick Look Preview, very fast.

More features for further less overhead.
Download from Releases
-Fixed slider knob
-Fixed subseconds time display
-Fixed UTI conflicts, now supersedes MKV previewing no matter which other media player is already present

New! Picture-in-Picture - additional panel that floats above Spotlight, Dock and the Menu-bar.
New! Bookmarks - custom markers on the slider, draggable.
New! A-B looping - custom repeat with the markers.
Improved - Controls bar, slider, settings.
Improved - Engine - demux with FFmpeg, toggle hardware acceleration on/off.
Improved - seeking/scrubbing - fine-tunable into possibly the most comfortable.
Lightweight as in up to 8 times less RAM overhead / average memory usage than Iina.¹

Notarized and sandboxed, works on all macOSX versions on both Intel and M-series architectures, from Big Sur 11 to Tahoe 26.

Instant playback and smooth scrolling tested up to 3840 × 2160 with a 10-bit bit depth and a bitrate of 365.20 Mbit/s.

• Passes all mkv-testing-files and all Jellyfish bitrate test files.

Launch the app once. This registers the extension as the extension itself stays within the app bundle.
Requires nothing that is not included already, is sandboxed and hardened, and has no extra entitlements. iina users might need to disable Iina thumbnails preview generation in the settings of 'iina'.

Delete the app.

This version has a new bundle identifier, might need to remove or desactivate from macOS' Settings the previous QL MKV
Replace the older app with the newer app. MacOS looks for the extension in the app, if app is moved, macOS can get confused and still look for it in the previous location.

Download the new QLCodec-MKV-Quicklook from Releases.

Or try QLCodec that quicklook-plays all non-natively-supported formats such as .mkv .wmv .flv .webm .rm, ... even .nuv.
Instant playback even from network volumes, Repository

First test on first version, testing responsiveness when browsing/scrolling in mkv sample videos of high bitrates (20, 110mbps) in HD, and ultra high bitrate (250mbps) in 4K UHD.

an extension that quicklook-plays virtually all non-natively-supported formats such as wmv flv webm rm, ... even .ivf or .nuv. No network-volumes issues, instant playback from NAS as well Repository

FFmpeg for their libraries licenced in LGPLv2.1.
VideoLan for their libraries licenced in LGPLv2.1.

A mac is a mac and it needs to stay comfortable, but it's still your mac.