[FFmpeg-user] re-encoding yields lots of messages

[jd1008]

like these:

warning, clipping 1 dct coefficients to -255..255:01:32.86 
bitrate=9711.2kbits/s
buffer underflow i=0 bufi=234794 size=338165me=01:01:47.43 
bitrate=9705.8kbits/s

The encode command is:

ffmpeg -i The_Previous_River_Trip.mp4 -vcodec mpeg1video -s 1920x1080 
-q:v 1 -y The_Previous_River_Trip.mpg

The mpg file seems to play just fine.

I just want to know what other parameter should I add to prevent 
underflow, and clipping.

Thanx!!