[MPlayer-users] B frames vs filesize question
Steven M. Schultz
sms at 2BSD.COM
Sat May 25 20:11:01 CEST 2002
Hi -
I'm seeing something strange that has me puzzled.
On other occasions I have added the 'vmax_b_frames=2' to the commands
and the resulting file was quite a bit smaller than without B frames.
Tonight the output file is the same size with or without the
vmax_b_frames=2 option. Would this indicate that somehow B frames
are not being generated?
With a 16 minute movie (~29000 frames) this script:
--------------
#!/bin/sh
rm -f frameno.avi lavc_stats.txt title1.avi
mencoder -v -dvd 2 -aid 128 -vop scale=320:240 -sws 2 \
-oac mp3lame -lameopts vbr=3:br=128:q=4 \
-ovc frameno -o frameno.avi
mencoder -v -dvd 2 -aid 128 -vop scale=320:240 -sws 2 \
-ovc lavc -lavcopts vcodec=mpeg4:vbitrate=500:vhq:keyint=150:vpass=1 \
-oac copy -lameopts vbr=3:br=128:q=4 -o title1.avi
mencoder -v -dvd 2 -aid 128 -vop scale=320:240 -sws 2 \
-ovc lavc -lavcopts vcodec=mpeg4:vbitrate=500:vhq::keyint=150:vpass=2 \
-oac copy -lameopts vbr=3:br=128:q=4 -o title1.avi
----------------
produces an avi file:
-rw-r--r-- 1 sms staff 74696180 May 24 00:42 title1.avi
But the script:
---------------
#!/bin/sh
rm -f frameno.avi lavc_stats.txt title1.avi
mencoder -v -dvd 2 -aid 128 -vop scale=320:240 -sws 2 \
-oac mp3lame -lameopts vbr=3:br=128:q=4 \
-ovc frameno -o frameno.avi
mencoder -v -dvd 2 -aid 128 -vop scale=320:240 -sws 2 \
-ovc lavc -lavcopts vcodec=mpeg4:vbitrate=500:vhq:vmax_b_frames=2:keyint=150:vpass=1 \
-oac copy -lameopts vbr=3:br=128:q=4 -o title1.avi
mencoder -v -dvd 2 -aid 128 -vop scale=320:240 -sws 2 \
-ovc lavc -lavcopts vcodec=mpeg4:vbitrate=500:vhq:vmax_b_frames=2:keyint=150:vpass=2 \
-oac copy -lameopts vbr=3:br=128:q=4 -o title1.avi
--------------
produces a file:
-rw-r--r-- 1 sms staff 74646636 May 23 23:52 title1.avi
Only about 50000 bytes difference between the two file sizes - that
seems quite small.
Should there be a larger difference in file sizes? Using B frames
has made a larger difference in the past so I'm wondering if they've
been (accidentally) disabled.
Cheers,
Steven Schultz
sms at 2bsd.com
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