From a forum on the web:

<code>
"I use Plex to get my video to the Roku, since it will do 
the transcoding on the fly. That way I don't 
have to keep two copies of all the recordings. I
just use mythlink to populate the folder Plex looks at...
I found this format to work well:

mythlink.pl --link /var/lib/mythtv/plex/ --format %U/%T/%T\ %pY-%pm-%pd%ph:%pi
</code>

Plex can be downloaded from here:

http://plex.tv