If you want to have a block of code run, just write a script. The following script opens the video player, loads a movie and plays it:
runMCI
| mci |
mci := (self subpartNamed: 'Media Control Interface').
"Open the digital video device."
mci send: 'open digitalvideo wait'.
"Load the tahiti movie. It must be in the current directory.
Or you must specify a full path name in the command."
mci send: 'load digitalvideo tahiti.avi wait'.
"Play the movie and don't return until the movie is done."
mci send: 'play digitalvideo wait'.
"Close the digital video device."
mci send: 'close digitalvideo wait'.