[MEncoder-users] mencoder losing bits?

[Corey Hickey]

Jason Bodnar wrote:
> Hi,
> 
> I'm trying to rip and encode a segment of a dvd using the following command:
> 
> mencoder dvd://1 -chapter 7-7 -oac copy -ovc lavc -lavcopts
> vcodec=msmpeg4v2:vbitrate=3072 -aspect 16:9 -ofps 24000/1001 -endpos 129 -vop
> crop=720:405:8:58,scale=736:522 -o
> grosse_pointe_blank-720:405-3072kbps-msmpeg4v2.avi
> 
> which works just fine. But when I play the video back with mplayer I see:
> 
> VIDEO:  [MP42]  720x405  24bpp  23.976 fps  2128.9 kbps (259.9 kbyte/s)
> 
> So, why is the video bitrate of the resulting file not the sames as what I
> specified (3072)?
> 

You're only using 1-pass encoding. With only one pass, mencoder's
bitrate use is only an estimate based on vbitrate and what it thinks it
can use. If you use two or more passes (see the vpass= parameter)
mencoder knows how many bits to allocate to each frame in order to meet
the target vbitrate.

In general, you should always use more than one pass so that mencoder is
able to allocate bits more accurately.

By the way, why are you using vcodec=msmpeg4v2 instead of mpeg4?
vcodec=mpeg4 is better, unless you have some constraints with regard to
the playback software.

-Corey