muxman Sub-Picture Stream问题

[xinzhan_56]

Item=Sub-Picture Stream
{
Stream Number=1
Display Mode=Wide/Letter
Item=Sub-Picture Play
{
File=f:\00001177.bmp
Time Code=NTSC
Display Area=0,0,719,480
}
}

00001177.bmp

must be 2bits 4bits or 24bits bitmap?

are ther any diference?