[Goodies-dev] Video thumbnailer

Dirk Vanden Boer dirk.vdb at gmail.com
Sun Feb 4 21:32:28 CET 2007

On 2/4/07, Erlend Davidson <E.R.M.Davidson at sms.ed.ac.uk> wrote:
> Dirk Vanden Boer wrote:
> > Hi,
> >
> > I created a thumbnailer for video files. I currently use
> > code.google.com <http://code.google.com/> as a repository for my code.
> > You can check out the thumbnailer at
> > http://code.google.com/p/thunarvideothumbnailer/.
> >
> > The thumbnailer uses ffmpeg for video decoding, so the supported video
> > files depend on the compilation of your ffmpeg library.
> > Dependencies of the thumbnailer are: ffmpeg and libpng.
> >
> > I would like some people to check out the thumbnailer, and let me know
> > if you find some bugs/problems that I'm not aware of.
> It seems pretty fast!
> I think there are a few bugs - quite often thumbnails look
> 1/2-transparent, or with some blocky-parts.  I get some errors:
> decodeVideoFrame() failed

I have never seen the transparent images. I will look into that. I am aware
of the decodeVideoFrame() failed error. This often happens immediately after
seeking in the file. But there is a retry mechanism, so this usually isn't a
big deal.

PIX_FMT_YUV420P will be used as an intermediate format for rescaling

This is printed by ffmpeg and is prefectly normal. This is done in the
conversion step from YV12 colorspace to RGB colorspace.

decodeVideoFrame() failed
> decodeVideoFrame() failed
> [mpeg1video @ 0xb7eba548]warning: first frame is no keyframe
> PIX_FMT_YUV420P will be used as an intermediate format for rescaling

These errors were when thumbnailing the file:
> http://www.stack.nl/~crypton/pguin/penguin1.mpg
> I'm using ffmpeg version 0.4.9_p20061016 (compiled under gentoo).

I'm personally using ffmpeg-0.4.9_p20070129 on gentoo but I don't think it
makes that big of a difference.

It might be an idea to check the thumbnail image for contrast, and if
> this is extremely low generate another one from another frame of the
> video... of course there are performance problems with doing that.

That's a pretty good idea. I'm now seeking to 10% of the file to avoid black
frames, but contrast checking would indeed be a further improvement. It will
indeed cost some performance, but I think it should be acceptable.

> Then maybe it can be included in the Xfce Goodies Project?
> I've been looking for a video thumbnailer for addition to the
> thunar-thumbnailers goodies project
> (http://goodies.xfce.org/projects/thunar-plugins/thunar-thumbnailers).
> Having a lightweight standalone program for video thumbnails seems like
> a good idea for a lightweight file-manager.
> Erlend
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