[MEncoder-users] Mosaic or Picture in picture filter for mencoder?

[FF]

Hello, i've been looking thru the mencoder docs and filters and I can't find
a way to do picture in picture.  I have two v4l2 video sources (/dev/video0
and /dev/video1), I would like to encode /dev/video1 and /dev/video0 at the
same time into the same file but have /dev/video1 offset and smaller then
(/dev/video0).  Basically, like an overlay.  To give you a better idea there
is a great example using ppmfilter ( http://users.pandora.be/acp/ppmfilter)
called video stacking: which will overlays one video on top of another which
is my goal.
ffmpeg2ppm bottom.mpeg |
ppmfilter --stack-video
top.mpeg --overlay position=60,10:30x30 |
ppmplay

Also there is a very nice Mosaic example
http://users.pandora.be/acp/video/check out
mosaic.mpeg.  In this example there looks to be more then 4 video captures
encoded into the same mpeg, each with its own dimensions.

Thanks for the help.
-ff