[MPlayer-users] "-vo pgm", as quickly as possible

[Bruce Janson]

I needed a way to decode MPEG files into greyscale frames, one
per file, and was pleased to discover that mplayer appeared to
provide such a feature with its "-vo pgm" argument.
However, I notice that it tries to maintain the "correct" output
frame rate as it does this decoding, which for my purposes is
unnecessary (and slows down the translation!).

How can I persuade mplayer to produce these .pgm files as
quickly as possible?