Windows Video (WMV) or Theora http://theora.org/
http://v2v.cc/~j/ffmpeg2theora/ The FFMPEG app is a really handy commandline encoder. So if you make a batch file with the standard encoding commands with the filename as a variable then you can assign a right click to the batch file as your encoding solution.
This is the code for the batch file. If you create a codecs folder in the windows folder and copy The FFmpeg theora exe in here and then rename it to FFMPEG2T.EXE also make sure the output is going to the right folder mine is on the F drive but you can change this.
@echo Please wait For Transcode to complete...
@ping localhost -n 3 >nul
echo c:\windows\codecs\FFMPEG2T -a 4 -A 63 -H 22050 -v 5 -V 500 -K 100 %1 -o "F:\TV\recordings\%~n1.ogv">c:\windows\codecs\go11.bat
rem echo if %~z1 GTR 5000 del %1>>c:\windows\codecs\go11.bat
msg /time:8 * Converted to Theora!
This will encode a video file using Theora Codev and the audio will be converted to 2205 Hz at 63 kbs. You can change these options but for what I want it's good enough.
Hope this gives you something to work with.
The Theora codecs are already packaged in an installer on the website. Works with the Direct Show Plugin.