@petrusoroaga
-b parameter is effective.
The default value is 17Mbps which is pretty big value for 1080p@30fps stream.

state->bitrate = 17000000;

The H.264 encoder of the chip will be encod the video below this value. If your scene is not complex, the actual bit rate of the encoding may be much smaller than this.

I'll tell you a test method. You can -b1000000, configure to 1Mbps, you can see the obvious difference in file size.