recently I've been working on a set of scripts for pre-generating thumbnails of video and picture files in a set of given directories. The idea is to be able to run thumbnail-generation in the background, per cron, per cmdline, not-in-X, not-using-nautilus, etc.
I've been reading a lot of documentation regarding this topic and I think I have come quite far in understanding all the details and requirements.
However I still need a little help (obviously...), but first, let me share my work with you...
Here is my three scripts:
batch_thumbnailer is the main scripts that calls vids+pics_thumbnailer, if in $PATH.
The syntax is: batch_thumbnailer [<dir> ...]
What it does is basically:
1. search the given directories (non-recursive) for files
2. determine the files mimetype and filter out all of type video/*, image/*
3. create a batch list for video files and process it with vids_thumbnailer
4. create a batch list for picture files and process it with pics_thumbnailer
The steps 3 and 4 are similar and can be broken down in sub-steps:
a. for each file, determine absolute path (file -> /path/to/file)
b. for each file, determine URI (/path/to/file -> file:///path/to/file)
c. for each URI, determine MD5 checksum (echo -n file:///path/to/file | md5sum | cut -c -32)
d. for each file, determine modification time (file.mtime = $(stat -c "%Y" file))
e. for each file, store a thumbnail under $HOME/.thumbnails/normal/$MD5.png with required metadata Thumb::URI := $URI and Thumb::MTime := file.mtime
(f.) if thumbnail generation has failed, move thumbnail to $HOME/.thumbnails/fail[/$0]/$MD5.png
The one place to start reading about thumbnails is probably:
So that's that.
Now I've created a whole batch of thumbnails with my scripts, however my problem is that nautilus is still recreating every single media file when I change to it's directory. I notice this because obviously it takes some time to display the thumbnails and also the mtime of the thumbnail is updated when re-/overwritten.
My idea in the first place was to have the thumbnails created and then nautilus is just displaying them superfast, since they already exist. However, this is not the case.
I spent some time figuring out the differences between my thumbnails and nautilus thumbnails, but I cant really tell the differences nor explain the "overwriting/recreating" behavior of nautilus. What I have tried so far is, I noticed another optional tag in the pings "Software: GNOME::ThumbnailFactory" and recreated that in my scripts, ... still with no change. Nautilus seems to allways overwrite my thumbnails.
That makes me wanna stop any further work on my scripts, because I must first know what the real problem is or else I waste my time.
FYI, these are my thumbnailers in nautilus (gconf-editor -> /desktop/gnome/thumbnailers/...):
- image x-pict := /usr/bin/gm convert -size %s -resize %s +profile "*" %i %o
- video@<any> := /usr/bin/ffmpegthumbnailer -s %s -c png -f -t 50%% -i %i -o %o
I would like to know in what way GNOME's thumbnail creation standard differs from the one described in  or whether nautilus/gnome stores extra-information elsewhere (outside $HOME/.thumbnails). My goal is the pre-create thumbnails in my scripts, that nautilus can actually use and instantly display, without re-creation/overwrites.
Thank you for all support, answers and feedback in advance,
it's all welcome.
PS: I've been forwarded to nautilus-list gnome org from gnome-list gnome org: