In my simple test script I'm using ShellExecute to open an avi file in BSPlayer (the file's default player).
ShellExecute("testvideo.avi","-hide")
When I run the script the video "testvideo.avi" does indeed open in BSPlayer, but the BSPlayer GUI is visible.
"-hide" is a command line option that is supposed to hide the BSPlayer GUI, leaving just the video visible.