Hi Marce,
Excuse me if I'm wrong, but I detect a bit of uncertainty. Your original post is a little confusing to me.

Correct me if I'm wrong- I think what you are trying to do is send a full resolution video to the Nokia. Then you want to play that on the nokia, without creating any extra files on the nokia.

I see a couple of problems. Firstly, you are transferring a LOT of data to the nokia. For example, a full length DVD would be over 4Gb. That will take a lot of storage space and some time to transfer.

Secondly, the nokia is not powerful enough to re-encode the video on the fly while you watch it, as has been pointed out. Theoretically you could transcode the video on the Nokia before watching it, but that would take quite a while (processing power limitation again), plus you would need even more storage space (0.3 to 0.8Gb) for the converted file, and probably the same again for temporary files created during the conversion.

The way around all this is to covert (transcode) the files on your computer (laptop or desktop), then transfer the converted files over to the nokia. That way the file you transfer is smaller (0.3 to 0.8Gb) and can be played directly on the nokia.
There are a number of ways to convert the video on your PC. It depends what operating system you have. Media converter works on Windows and on Mac or Linux machines. There are other options listed on that wiki page also.
Theres also some more help to be had here Converting (re-encoding) videos, playing music, ebooks.

The bottom line is convert the video on a PC to a format the mobile device can handle, then transfer just the converted file.

Hope that helps.