my $in_width = 640;  # this depends on your input data
my $in_height = 480; # this depends on your input data
my $width = 320;     # this depends on what you want
my $height = 200;    # this depends on what you want
my $file = 'test.mpg';

my $ffmpeg = 'bin/ffmpeg.exe';
my $pixel_format = 'rgb';

my $pid = open my $output, 
               sprintf qq{| %s -y -f rawvideo -pix_fmt %s -s ${in_width}x${in_height} -i "-" -f mpeg2video -s ${width}x${height} "$file"},
               $ffmpeg, 
               $pixel_format
    );

for my $frame (@frames) {
    print $writer $frame;
};