Excuse my bad english.

A have a Joomla 2.5.4 and your plugin (last version).

I have a small video-file in a /images/video/ folder.
In K2 component in article i insert this code:

{3gpremote}mmm-evolution.com/images/video/VIDEO0004.3gp{/3gpremote}
{3gp}VIDEO0004{/3gp}

I can see the player. Also i can push the "play" button, but video does not playing. A black screen of player only. See this:

mmm-evolution.com/advanced/123

Did you try any other video format?