FFV1 is a ffmpeg lossless format - monster size files.
You would think that just adding the libavdevice/libavcodec-extra packages would work but no.
This is in a fairly basic LM11 virtual machine, so I can revert any changes. Tried the above, then added the gstreamer packages. No real success.
Back to basics,
In the multimedia menu, "install-multimedia-packages" adds a whole load of junk but it does work here. gMplayer will play a little 24 sec 50 MB ffv1 avi file.