[MPlayer-users] Are mencoder lossless codecs really lossless?

[James Board]

My input file is an uncompressed raw YUV 4.2.2 format.  I want to compress individual frames with a lossless codec.  My mencoder implementation listed three such codecs it the man page: 
	* ljpeg: lossless jpeg
ffv1: FFmpeg's lossless video codec
	* ffvhuff: nonstandard 20% smaller HuffYUV using VY12
I encoded my file using the following:
    mencoder -ovc lavc -lavcopts ljpeg -oac copy -o out.avi in.avi
And then I converted it back to raw pixels with
    mencoder -ovc raw -oac copy -o out2.avi out.avi
The above two steps should regenerate exactly the original file in.avi, right?  I did this with the three lossless codecs I listed above.  The problem is that my original input file in.avi is bigger than the final output file out2.avi: they should be exactly the same, right?
 
So, my question is this: are those codecs really lossless?  Bit-exact lossless?  Or are they merely pretty good?