[MPlayer-users] mplayer -dumpstream vs mencoder -oac copy -oac copy

[ap2003 at libero.it]

I'm a mplayer/mencoder newbie and I would like to use mplayer/mencoder to save mms:// streams.

I understand you can do this either with mplayer or mencoder, as follows 

$ mplayer -dumpstream -dumpfile test1.wmv mms://...

or

$ mencoder -oac copy -ovc copy -o test2.avi mms://

I expected the same results, while with the following 30 seconds trailer 
mms://rntlivewm.rai.it/rai/raitv.wmv
I get a file of 1.3 MB with the first command and 2.0 MB with the second.

So, what is the difference between the two commands? Does the second one have a better quality, or a worse compression, or what?

Thanks in advance!