Mencoder with same quality output

Ok, first things first...

ffmpeg's sameq option doesn't mean same quality, and in many cases will not do anything relevant.

This is from the ffmpeg man page:

-sameq
       Use same quantizer as source (implies VBR).

This is actually from the ffmpeg online documentation

‘-same_quant’
Use same quantizer as source (implies VBR).

Note that this is NOT SAME QUALITY. Do not use this option unless you know you need it.

You can check it here http://ffmpeg.org/ffmpeg.html, search for same_quant (it's the same as sameq).

Ok, now that's out of the way,

I don't know exactly what you are trying to achieve with your conversion, but there are 2 possibilities, which I will enumerate and try to help:

1. You are only trying to change the Container and not the codec of the video. The container is the bit of data that's there to tell the software that's trying to play the video how things are organized, It has the info on the FPS, video codec, audio codecs, how the data is stored. If your video was water the container could be a glass bottle a cartoon, or plastic bottle. In this case containers are wmv, avi, mp4, mov, etc. Containers are important because not all of them support all codecs, and not all software supports all containers. Keep in mind that you could still get the container right, but if the video inside is the wrong codec you're still out of luck. So if you only want to change containers you can use:

       mencoder file.wmv -ofps 23.976 -ovc copy -oac copy -o file.avi
   

2. You're trying to change the Codec. The Codec is the algorithm or set of specs that actually says how a video is encoded, different codecs have different quality outputs, sizes, parameters, etc. Now things get a bit tricky, while changing the container you can actually copy the video and not lose any quality (because you only change the container) when changing codecs you will most certainly lose some quality, but most times if both codecs are good and the right parameters are configured you wouldn't notice much after just one conversion (this is inherent of the way codecs compress video ).

The different quality between ffmpeg and mencoder I can only guess, but one of two things must be happening:

1. You only need to change containers, and ffmpeg is detecting that and only copying the video. (if this is the case use -ovc copy on mencoder)

2. You need to change codecs and ffmpeg is choosing better codecs/parameters to recompress the video. In this case try to check what codec ffmpeg is using (if you can't post them here and I will take a look) or try a diferent code with mencoder (right now you're not specifying anything) for example:

   mencoder file.wmv -ofps 23.976 -ovc lavc -lavcopts vcodec=mpeg4 -oac copy -o file.avi
   

This would make use the ISO standard MPEG-4 (DivX 5, XVID compatible), of course you could still need to change the bitrate that reconversion is using, looking at the source bitrate would be a good indicator.

Also mencoder supports a lot of different libs, some are multi codec like lavc, others not, try

mencoder -ovc help

to get a list of supported codecs, in mine I got:

MEncoder SVN-r33094-4.5.3 (C) 2000-2011 MPlayer Team

Available codecs:
   copy     - frame copy, without re-encoding. Doesn't work with filters.   
   frameno  - special audio-only file for 3-pass encoding, see DOCS.
   raw      - uncompressed video. Use fourcc option to set format explicitly.
   nuv      - nuppel video
   lavc     - libavcodec codecs - best quality!
   libdv    - DV encoding with libdv v0.9.5
   xvid     - XviD encoding
   x264     - H.264 encoding

So I could do:

    mencoder file.wmv -ofps 23.976 -ovc xvid -oac copy -o file.avi

or

    mencoder file.wmv -ofps 23.976 -ovc x264 -oac copy -o file.avi

For a smaller file size and looooonger compress time