[FFmpeg-user] Piping from FFmpeg to FFplay

[Michael Koch]

I have a question about piping from FFmpeg to FFplay (in a Windows batch 
file):

ffmpeg -f lavfi -i testsrc2 -f nut | ffplay -

This command line works fine and I have used it many times. But I don't 
know what's the meaning of the - character after ffplay. Does this - 
character belong to the ffplay command? What does it mean? Or is it a 
batch file operator, like the | character?
I can't find - without any following characters in the FFmpeg or FFplay 
documentation.

Michael