I've just updated my ffdshow to the latest ffdshow-alpha, and I think I've found a way to force YUY2 with it (or at least to prevent it from using YV12).
Open ffdshow options and select "Codecs" menu.
In "Supported output colorspaces" settings, just uncheck"YV12".
The video should then play nicely in BSplayer's overlay mode 1.
I also used to have jumping dots while using ffdshow (I use these filters to play most of my videos: DivX3, 4, 5 and XviD), and looks like they've just vanished! ^_^
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