VeryDOC Flash to BMP Converter Command Line can extract images from video. Meanwhile you can edit the size of the output image file. Say you can specify the width and height for the output image file.

Flash to BMP Converter Command Line supports these options:
1.-in: specify input SWF file name
2.-out: specify output image file name.
3.-width and -height: set the width and height of converted image.
4.-timer: set the capture interval of conversion, in unit of millisecond.
5.-hidewindow: hide the progress dialog during conversion.
6.-$: register the application with a registration key.