[MPlayer-users] file sizes with and without B frames

[Steven M. Schultz]

Hi -

	DaI thought using B frames would produce smaller files since B
	frames are smaller than I frames.

	Encoding a ~8min movie segment with and without B frames produces
	files that are perhaps 1% different in size - is the correct or
	am I not running mencoder correctly?

	With the command:

... | mencoder -sws 2 -vop scale=480:480 \
  -ovc lavc \
  -lavcopts vcodec=mpeg4:vhq:vbitrate=1500:keyint=100:vpass=1  \
  -audiofile foo.wav -oac mp3lame -lameopts br=128 -o foo.divx -- -

	(and of course the matching ":vpass=2" run)

	the output file is 106346860 bytes long

	With the command (and its matching pass2 run)

mencoder -sws 2 -vop scale=480:480 \
  -ovc lavc \ 
  -lavcopts vcodec=mpeg4:vhq:vbitrate=1500:keyint=100:vmax_b_frames=2:vpass=1 \
  -audiofile foo.wav -oac mp3lame -lameopts br=128 -o foo.divx -- -

	the output file is 106264760 bytes long.  That's only 82100 bytes
	smaller than not using B frames.

	Am I missing some options that might make using B frames worthwhile?

	Thanks.

	Steven Schultz
	sms at 2bsd.com