Ubuntu – Nautilus not generating thumbnails for GIF images

There is a way of getting this done explained in the Floorplanner Tech Blog. To compile dump-gnash on a fresh Maverick you'll need

sudo apt-get install gcc libboost-dev libboost-thread-dev libagg-dev libsdl1.2-dev libcairo-dev libgstreamer0.10-dev libatk1.0-dev libglib2.0-dev libpango1.0-dev libgtk2.0-dev libgtkglext1-dev libgl1-mesa-dev libgif-dev libjpeg-dev libgstreamer-plugins-base0.10-dev libspeex-dev libcurl-dev

And then you just follow the steps. This will take a long time.
NOTE: For Step 7 use the following script instead:

if [[ $3 ]]; then
    raw="$(mktemp)"
    dump-gnash $2 -P "FlashVars=url=file://$1" -D "$raw" --max-advances 1 -j 500 -k 500
    tail -c 1MB "$raw" | convert -size 500x500 -depth 8 rgba:- -separate -swap 0,2 -combine -trim png:"$3"
    trap "rm $raw" EXIT
else
    echo "Insufficient arguments (expected 3 arguments)"
    exit 1
fi

Once you have the final script running you just hook it into gconf-editor

gconftool-2 -s "/desktop/gnome/thumbnailers/application@swf" -t string "/usr/bin/swfthumbnailer.sh %s %i %o"
gconftool-2 -s "/desktop/gnome/thumbnailers/application@swf/enable" -t boolean 'true'
gconftool-2 -s "/desktop/gnome/thumbnailers/application@x-swf" -t string "/usr/bin/swfthumbnailer.sh %s %i %o"
gconftool-2 -s "/desktop/gnome/thumbnailers/application@x-swf/enable" -t boolean 'true'
gconftool-2 -s "/desktop/gnome/thumbnailers/application@x-shockwave-flash/command" -t string "/usr/bin/swfthumbnailer.sh %s %i %o"
gconftool-2 -s "/desktop/gnome/thumbnailers/application@x-shockwave-flash/enable" -t boolean 'true'

Then restart (or restart gnome-settings-daemon), and you've got swf thumbs!

P.S.: This is a huge hack. A better way to do this would be vastly appreciated.

Digging up further (and researching a LOT), I figured it out:

About image thumbnailers: It seems that Nautilus uses libgnome-desktop for thumbnail management, and the latter uses libgdk-pixbuf to handle file types that have no external handler in /usr/share/thumbnailers. So the "basic" image types are ultimately handled by GnomeDesktopThumbnailFactory and GdkPixbuf (references shown for versions shipped in Ubuntu 12.04). And the formats it handles can be inspected using the gdk-pixbuf-query-loaders tool. In my system this means:

The GdkPixdata format
['gdkp']
['image/x-gdkpixdata']

The Sun raster image format
['ras']
['image/x-cmu-raster', 'image/x-sun-raster']

The PNG image format
['png']
['image/png']

The WBMP image format
['wbmp']
['image/vnd.wap.wbmp']

The JPEG image format
['jpeg', 'jpe', 'jpg']
['image/jpeg']

The ANI image format
['ani']
['application/x-navi-animation']

The TIFF image format
['tiff', 'tif']
['image/tiff']

The XBM image format
['xbm']
['image/x-xbitmap']

The PCX image format
['pcx']
['image/x-pcx']

The Targa image format
['tga', 'targa']
['image/x-tga']

The PNM/PBM/PGM/PPM image format family
['pnm', 'pbm', 'pgm', 'ppm']
['image/x-portable-anymap', 'image/x-portable-bitmap',
 'image/x-portable-graymap', 'image/x-portable-pixmap']

The JPEG 2000 image format
['jp2', 'jpc', 'jpx', 'j2k', 'jpf']
['image/jp2', 'image/jpeg2000', 'image/jpx']

The ICNS image format
['icns']
['image/x-icns']

The BMP image format
['bmp']
['image/bmp', 'image/x-bmp', 'image/x-MS-bmp']

Windows Metafile
['wmf', 'apm']
['image/x-wmf']

The QTIF image format
['qtif', 'qif']
['image/x-quicktime', 'image/qtif']

Scalable Vector Graphics
['svg', 'svgz', 'svg.gz']
['image/svg+xml', 'image/svg', 'image/svg-xml', 'image/vnd.adobe.svg+xml',
 'text/xml-svg', 'image/svg+xml-compressed']

The ICO image format
['ico', 'cur']
['image/x-icon', 'image/x-ico', 'image/x-win-bitmap']

The XPM image format
['xpm']
['image/x-xpixmap']

The GIF image format
['gif']
['image/gif']

So these are the "internal" thumbnailers. And it does include xpm files. So something was wrong with my particular files instead.

And indeed the files were not standard, they had a copyright note prior to the /* XPM * header:

// This file is part of BOINC.
// http://boinc.berkeley.edu
//

/* XPM */
static const char *atiicon_xpm[] = {

Once comments were removed, thumbnails were generated just file.

It is curious that even with the "invalid" header the default Image Viewer in Gnome ("Eye of The Gnome", or eog) was able to display the files! So either files are not actually invalid, or kudos to eog for being able to open them! Anyway, since it is possible to open, and eog uses gdk-pixbuf too, I've filled a bug in libgnome-desktop requesting that thumbnailers be generated for such non-standard xpm files. Any help promoting the bug is appreciated!

Also, some notes about my research:

ThumbnailerSpec is mentioned in several places as the specification for "external thumbnailers". But it has nothing to do with this! It talks about using D-Bus for thumbnailers management, and nothing indicates that such spec is actually implemented in Gnome.

Actually, I was unable to find any official spec on the implemented behavior of "saving a .thumbnailer file with [Thumbnailer Entry] and .desktop-esque format to /usr/share/thumbnailers". Bug 636819 is cited a lot as a source, but it only describes that behavior was changed in Gnome2->Gnome3 transition, and it no longer uses gconf to store external thumbnailers.

It looks like there is no spec at all. This obsolete documentation is still the only official reference, for example, on what %i %o %u %s means.

And the only "official" place announcing the change from gconf to /usr/share/thumbnailers, other than hunting down the source code commit that did it, is this seemingly ordinary bug report.