How can I create a thumbnail from a photo or a video with the standard OS X tools? I mean, Finder is able to do it, so (being a Linux user), I expect to be able to do exactly the same without the GUI; is it possible?
It's far from perfect however you can use the save the thumbnail that Quick Look generates in the Finder by running the following command:
By default this produces a 128x128 png. Removing the
To make it larger add the
If you want better results (eg. choose your frame) I recommend using MacPorts to install ffmpeg or ImageMagick. (See fideli's answer)
To expand on www.haykranen.nl's post, install ffmpeg and ImageMagick using MacPorts.
For pictures, create a thumbnail using (i.e. fits within 250x90):
More info here.
For movies, create a thumbnail using:
Unfortunately, these tools aren't standard OS X tools. Your suggestion about how Finder is able to do it likely happens through a QuickTime or CoreVideo method that isn't easily accessible at the command line.
I'm not sure if there's a native command available for that, but you could always try installing ffmpeg from MacPorts, or alternatively (for photos), ImageMagick.