ffmpeg changing video frame rate

Hi, I downloaded a show from the BBC iplayer. I had been advised to expect a frame rate of 50 fps hence a high bit rate.
Quote:

Duration : 58 min 58 s Source duration : 58 min 58 s Bit rate : 2 619 kb/s Maximum bit rate : 2 734 kb/s Width : 960 pixels Height : 540 pixels Display aspect ratio : 16:9 Frame rate mode : Constant Frame rate : 50.000 FPS

I don't know whether I am expecting too much. I would like to lower the frame rate while keeping other video aspects the same. I decided to ramp down to 25 fps. The first attempt changed height & width so I added the "-vf" qualifier.

Quote:

ffmpeg -i file -r 25 -vf "scale=960:540" output

This gives me:
Quote:

Duration : 58 min 59 s Bit rate : 854 kb/s Width : 960 pixels Height : 540 pixels Display aspect ratio : 16:9 Frame rate mode : Constant Frame rate : 25.000 FPS

I was expecting the bit rate to drop but that seems a huge drop. Is this to be expected? Is there a recommended path to lower the frame rate?

Cheers