Add tags using file name

Hey guys
let me introduce you the situation.

I'm downloading a lot of videos on YouTube using batch.
Those appear as "video.mp4" in a folder named "20111212-Biloulette-la vidéo d'aujourd'hui", so as "Date-uploader-title". So i'd like to put tags in "video.mp4" using the name of the folder that way : %date%-%artist%-%title%.

How ? Because i can't find how to use the folder name instead of the file name.

You were on the right track. Use Convert>Filename - Tag but instead of

Please note that %date% is no standard field. It should either be YEAR or RELEASETIME.

Oh. My. God.
Thank you so much.
Another question, then.
I'd like to do this in a .bat, how?

if you mean that ".bat" is an action then use an action of the type "Guess value"
Source: %_directory%
Target: %date%-%artist%-%title%

Actually, i'd like a command to say :
Use mp3tag and put tags on video.mp4 using "Convert>Filename - Tag" with %releasetime%-%artist%-%title%

Don't know if i'm correctly explaining.

There is no way to call any functions inside MP3tag by the means of command line parameters.
So a traditional command shell batch file can (only) open a single file or a folder but cannot start any further functions.

The idea is not to have to import the video in mp3tag, to write %year%-%artist%-%title%%dummy% and to do "save".

Since i'm downloading thousands of videos, i want it to be automatical !

I don't understand why you can't modify your workflow.
You can download as many files as you want, load them all into MP3tag in one go and then extract the data from the folder name.
If you insist on a workflow with a command line option then it is, as I said, not possible.