Troubleshooting

First, please check that you're running the latest version, log out of macOS and back in again and see if the problem remains.

Finder doesn't show thumbnails and/or previews for any "non-native" video files

Under System Settings → General → Login Items & Extensions (scroll to the bottom) → Extensions → Quick Look → ⓘ → QuickLook Video ensure that Video previews and Video thumbnails are checked. Try unchecking and checking these settings. (Note that these settings are under System Settings → Privacy & Security (scroll to the bottom) → Extensions → Quick Look on older versions of macOS).
Run the QuickLook Video app and press Refresh. This tells QuickLook to clear its thumbnail cache and then restarts Finder to make it refresh its thumbnail cache.

Unfortunately macOS doesn't allow this app to handle displaying previews of the following "native" file types: .avi, .dv, .m4v, .mov, .mp2, .mp4, .mts, .ts, .vob. This may be fixed in a future release.

If the problematic files reside on an external or remote volume check that you have write access to the volume - see Change permissions for files, folders or disks on Mac. Once you've granted yourself write access, you'll need to force Spotlight to re-index the files as described below.
Ensure that you haven't disabled Spotlight indexing using any of the methods discussed here.
Spotlight can be slow to notice new plugins. You can check whether Spotlight has found the plugin supplied by this app by typing mdimport -L in the Terminal and checking whether "/Applications/QuickLook Video.app/Contents/Library/Spotlight/Video.mdimporter" is listed. If it isn't listed, then check whether you have any other copies of the QuickLook Video app lying around (Spotlight doesn't like multiple copies). You may have to log out and back in again.
If you see a message in the QuickLook Video app about high CPU and disk usage then Spotlight has found the plugin and the app has asked it to re-index video files. Re-indexing happens in the background so it may take a few minutes before you can see the metadata in Finder.
Once Spotlight has found the plugin:
- You can force it to re-index video files by copying the following, pasting in the Terminal app, and pressing Enter:
```
mdimport -r "/Applications/QuickLook Video.app/Contents/Library/Spotlight/Video.mdimporter"
```
- Alternatively, you can force Spotlight to re-index all the files in a folder with mdimport -i /path/to/folder

Recent versions require macOS 12 "Monterey" or later on a late-2013 or newer Mac. The last version to support hardware older than this is Release 1.991.

You can't delete a file while QuickLook is thumbnailng or Spotlight is re-indexing it. And you can't Unmount a volume while QuickLook is thumbnailng or Spotlight is re-indexing files on it. Unfortunately you'll have to be patient until QuickLook and Spotlight settle down.

This happens when Finder can't store its thumbnail cache on the drive. Which can happen for several reasons:

The external volume is formatted as "MS-DOS (FAT)" or "ExFAT". Please reformat your external volume as "Apple File System (APFS)" or "Mac OS Extended" if possible (which will give you better performance under macOS in general).
You have told Finder not to save the .DS_Store files that it uses to cache thumbnails. You can check this using the Terminal app:
```
defaults read com.apple.desktopservices DSDontWriteUSBStores
```
or
```
defaults read com.apple.desktopservices DSDontWriteNetworkStores
```
Both will show 1 if you've disabled the .DS_Store files, and 0 or The domain/default pair ... does not exist if you haven't. You can re-enable the .DS_Store files with:
```
defaults write com.apple.desktopservices DSDontWriteUSBStores -bool FALSE
```
or
```
defaults read com.apple.desktopservices DSDontWriteNetworkStores -bool FALSE
```

You may have better results with a specialised editing tool such as Subler for MP4/M4V files, or MKVToolNix for MKV/WEBM files.

From the QuickLook Video app's Help menu, choose Report an Issue.
Drop any problematic file and press Send.
Give the new Issue a title, describe the problem and press Submit new issue.