How to tame the Windows Thumbnailer

Wait, what?

The Windows thumbnailer is a feature which allow to see previews* of files when you are in thumbnail mode in windows explorer.

Which Windows I need?

Tested with windows10, but I’m pretty sure will work even on 7 and on 8/8.1. Maybe even vista.
Even if the cache is hardly changed, I can’t assure it works with XP or previous. Try on your risk.

What files are covered?

Actually, any media file should be covered, but windows only fetch some of them (due lack of codecs):

  • Audio files (mp3,wma,flac,ogg,..): I don’t the see the point to preview audio files as you can’t listen the preview at all.
  • Image files (png,gif,jpg,bmp,…): Windows cover most of them, but sometimes don’t fetch thumbs for newer file types like for example the .webp.
  • Video files (avi,mp4,mkv,flv): Windows has several troubles here. Why? As several videos use codecs which aren’t shipped with windows, so the preview is not possible.
  • Other files (txt,doc,swf,pdf): These types are a bit particular. So, the thumbnail may work or not as aren’t fetched with the aid of a codec. Txt and doc previews never worked on explorer for what I know. Pdf support is quite partial.

So why I need the guide?

The feature in windows may not work as expected. Why? As windows only generate previews for the codecs which ship with itself and, even worse, perform various clean-up operations to them. So, yes, it generates thumbnails, but it may need to re-create them if the system decide to wipe-out the temp folder or the various thumb.db files.

It removes clutter, what’s the problem?

This may not be a problem if you have folders with less than 1000 files. But if you have a folder in which you are storing a lot of preview-able files, it’s quite sure windows will wipe them very often.

So.. the thumb cache don’t exist?

Indeed it exist. But it is just no persistent. So, if you have folder with a lot of files – lets say more than 10000 – any time you access to it in preview mode, explorer will grab the thumbs again, as windows removed them.

So.. there’s a solution?

Windows doesn’t provide that, but there is a sort of workaround which involve some external tools

  1. A codec pack: You may skip this if you don’t feel comfortable with the operation but some files, especially several video files – mainly .webp, (several) .mp4 and .avi, .mkv, .flv and others – simply won’t have a thumb.
  2. Icaros thumbnailer: A cool software which allows to empower what windows explorer can preview or not. And especially improve the caching system.
  3. An autohotkey script which make easier to fetch thumbs from windows explorer to icaros: when everything is in place, icaros and this small script will work in synergy.

It this safe?

Codecs and software (when clean) usually won’t harm the machine. But, as general rule, follow the tips to avoid any problem: do regular backups, a restore point before install codecs, know what you are doing and uninstall these tool and the codecs if you have issues. The guide come without warranties. But it doesn’t harm my main machine. So the choice is up to you.

My machine is old. Can I still try this?

Depends on how is “old”. More thumbs means more system resources usage during thumb fetches. If it is really old, probably is not suggested. On the other side, folder in preview mode will be faster, as you actually cached the previews: windows don’t have to load them again and again.

Why I need a codec pack?! VLC reproduce everything*!

Is not essential, but highly suggested. VLC player actually reproduce almost everything simply as it uses “its own” codecs: which often are the same found in the codec pack.

# 1 – Which Codec Pack I need?

Kazaa Lite mega codec pack. Why? Is one the most complete codec pack ever made and it allows to choose what you want in the installer. If unsure, let it decide 😉
You can still use the guide skipping this point, but you’ll have several missing thumbs. If you don’t feel comfortable with the operation, please skip this point anyway.

# 2 – Icaros thumbnailer

After codec pack installation, reboot the system and install icaros. Set-up as it follows:

  • Enable thumbnailing if it were disabled;
  • Choose the thumbnail filetypes you want to preview (click on picture icon);
  • Enable dynamic cache, then click on books icon and…
  • Choose cache location (in a drive with enough space);
  • Remove excluded types (if you want to store picture files thumbs too);
  • Set locations where icaros should use its cache. Or where it shouldn’t (below).


# 3 – Autohotkey script

Why I need this? What it does? My security products says it’s infected!!
It’s a macro tool, most of them (all?) are marked as suspicious or virus, but is not.
Feel free to send it to virus total (which will say malicious), whitelist and use it or do the follow operation manually but it would be really annoying with big folders.
The exe is just to avoid you to install autohotkey if you want to try it.
The ahk is the “source code”, so you can view what it does in notepad 😉
The script basically push the down arrow every “x” time to allow explorer to fetch any thumbnail in a folder, so even Icaros can grab them and store in its cache.
Then, when opened, the folder will use the cached ones instead recreating it any single time. Which is even more annoying.
The script could be really better, but I’m not expert on this.
Close the script (taskbar > H icon > exit) when the folder reached the end to avoid pressing down arrow on other apps.

# 4 – Additional notes (may change anytime)

  • Cbr and (most) swf previews don’t work. But they works with mediapreview. Just DON’T check anything else; Like pdf, fetching swf thumbs is slower.
  • Pdf previews needs Acrobat Reader installed. Open it and enable the thumbnail generation, under general in preferences. But support is not very good – and fetching thumbs is slower;
  • Webp images could need a codec to be open-able/preview-able;
  • Rebuild index in icaros needs a lot of time if stored thumbs are a lot (>1gb);
  • Remove cache in icaros imply that thumbs need to fetched again;
  • Probably, would be better put a max-size to thumb folder, as it can easily grow-up.
  • Any tip to improve the script (especially to make it target only windows explorer) is welcome.

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