I am new to video encoding so bear with me.

I am using FFMPEG. I have an mp4 file which is 640 x 350 with an average bitrate of around 2000kb (I think) and a filesize of 80Mb. I want to convert this to an ogv file with a much lower bit rate (128kb) but the same width and height. I am using the following command...

ffmpeg -i input.mp4 -b:v 128k output.ogv

... but FFMPEG seems to ignore my bitrate option and outputs a file with a bitrate of around 600kb and a filesize of around 3Mb.

I can do this using FFMPEG2THEORA using the following command ...

ffmpeg2theora -V 128 input.mp4 -o output.ogv

...but I was wondering if it was possible using FFMPEG.

Any ideas?