You're welcome. And to make it even easier here are some commands to do it from the command line.
To see what the current setting is:
mysql pluto_main -u root -e "SELECT Extensions FROM MediaType WHERE PK_MediaType=5"
+---------------------------------------------------------+
| Extensions |
+---------------------------------------------------------+
| mov,avi,mpeg,mpg,wmv,ts,tp,dvd,vdr,ogm,evo,m2ts,iso,mp4 |
+---------------------------------------------------------+
And to update it like Kir's example:
mysql pluto_main -u root -e "UPDATE MediaType SET Extensions='mov,avi,mpeg,mpg,wmv,ts,tp,dvd,vdr,ogm,evo,m2ts,iso,mp4,mkv,divx' WHERE PK_MediaType=5"
Now you can run the first command again to verify.