LW's media player only does audio files(mp3's). Videos will launch in your default player. You can enable or disable LW's player completely by going to Tools>Options>Player(in LW).
You could also change your default media player to something else. Open the folder with your files in it(in windows, not LW). Right click a file and click on Properties > then click on "Change" > choose a player from the list > click OK > Apply > OK. Do that for each file type you want to change.
How to set the Default applications