Media thumbnails and previews

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These are primarily notes
It won't be complete in any sense.
It exists to contain fragments of useful information.

Thumbnails are usually cached, because they take a bunch of CPU and IO to generate the first time, particularly for video.

Cached thumbnails are better than uncached thumbnails, so you probably want them unless you disable them altogether - and there are very few gradations in disabling. Still, If you have a particularly nice and snappy image viewer, and you don't need to see thumbnails in explorer because of it, you could disable that completely.

Metadata (such as music title and artist, photo details) (if and when displayed) often isn't cached, so takes a little IO each time.

Both draw resources, which you may not like if trying trying to squeeze the most time from your laptop battery, trying to get snappier network browsing, or slightly snappier response in general.

Windows - Video and audio explorer extensions (previews, metadata)

Windows XP has a Shell Media Extension, which includes the Media File Property Extractor. These will do things like:

  • show thumbnails for video files,
  • preview videos in the explorer view with the action choices on the left
  • read and show artist, album and such in detail view when it notices a directory contains mostly audio or video media

This can cause a number of annoyances, including:

  • slower loading of directories with a lot of audio/video media (because reading the metadata needs a lot of individual disk accesses) and of picture thumbnails (as there's a lot of rescaling going on. pre-generated thumbnails make this fast on subsequent browsing)
  • explorer hanging with 100% CPU use on bad video files (probably now a thing of the past)
  • since files are locked, trying to move or delete them while windows is working them will give you an error.
  • in the case of the 100% hang, it is very hard to delete them at all (also because loading the folder and clicking on the file will trigger the preview. One way of deleting them is to Control-X (cut) them, wait for explorer to give up if it does at all, then paste it into the recycling bin)
  • If you're very unlucky, you may hit Windows' deleting-while-busy-makes-the-file-non-deletable-even-with-the-command-line,-until-the-next-bootup bug

To disable video thumbnails -- you won't really miss it if you name things sensibly -- run the following (run dialog, or from 'cmd' - elevated cmd in Vista/Win7):

regsvr32 /u shmedia.dll

To re-enable:

regsvr32 shmedia.dll

There apparently is an alternative to this, deleting a registry key that causes windows to load this feature, but re-enabling takes a lot more work.

Image previews

The method is similar to the video preview, with another DLL. To disable:

regsvr32 /u shimgvw.dll

To re-enable:

regsvr32 shimgvw.dll

Thumbnail storage


Used by Explorer (mosty on 2000, XP?(verify)).

Thumbs.db is a hidden file, created on demand in each directory where there is something previewable. Windows stores its generated previews in here.

It is also one of a few sources windows can use when it wants to display what images are contained in a folder.

There are a few potential downsides too. Example: the Thumbs.db is unmovable while it is being accessed, so it may interfere with directory moves, picture directory uploading, and such.

It may also mess up directory content comparisons, and so on. These are things that only power users really care about, but still - if you usually use a something like Picasa anyhow, you probably don't need these files.

If you want to stop windows from creating this file, it should be: Any exporer window -> 'Tools' menu -> 'Folder Options' -> 'View' tab, and check the "Do not cache thumbnails" option.

ehthumbs.db, ehthumbs_vista.db

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Apparently used by (different versions of) Windows Media Center


This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Windows Vista (and 7?) store thumbnails per user, stored in their profile.

Used by Zoom Browser. Probably means you have software with your Canon camera.


This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Files that come from Mac OSX.

Analogous in function to windows's desktop.ini and Thumbs.db:

A per-directory cache of icons, icon positions, and more. Finder creates these on most directories it accesses, including network shares, USB drives.

Mostly invisible when viewed from OSX, unix derivatives often hide it because it's a dotfile, windows will show it.

See also