Here is how I would pull a steam from a radio station using .asf
mplayer -cache 4 -playlist http://126.96.36.199/JackFM?MSWMExt=.asf
Don't know what format 0x56444152 is... is this a quicktime .avi or a DivX .avi?
You can force Mplayer to use specific Audio and Video DRIVER's but I don't think you can force it to use a specific codec, but you'll have to find out what it is first.
Perhaps try your video with the -nosound option and see if the video is at least comming up...