Well well,
U bring up something i have been trying to find for a long time see as far as I know there is no video controller plugin example available for download or use as a reference. Such plugins (supporting 3gp) are built into some nokia phones supporting mmf.
I guess u will have to come up with the first open source video plugin

The devkit i have does not give any examples of plugins on the video side.

For some pointers u can look at
1. http://www.forum.nokia.com/info/sw.nokia.com/id/f07f6cef-1a32-46e6-8d33-279ea1555543/Symbian_OS_Creating_Video_Applications_In_Cpp_v1_0_en.pdf.html
2.http://www.forum.nokia.com/info/sw.nokia.com/id/ae9307f6-e8b3-455d-81fc-0442aabc5526/Symbian_OS_Multimedia_Framework_And_Other_Multimedia_APIs_v1_0_en.pdf.html

3. ogg vorbis controller (e.g for audio plugin with complex codec from symbian)

4. symbianoggplay on sourceforge.net ...(again audio but open source have written plugins to handle .ogg file)

if you find ne other useful info do let me know. best of luck
groys