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

[gabor farkas]

it works like this:

you want to put a video on a cd.

the cd has 700Mbyte of free space

so you take your video file, and make the audio-data let's say a
96kbit/sec mp3 file... that means 96kbit/s = 12kbyte/s.

let's say your video file is 1hour long.

the audio-data will have a size of 12*3600=43200kbyte=approx 42mega

so yuo have approx. 700-42=658MB=658*1024KB=673792KByte  place for the video data,
that means that for an 1hour video data,
it can be 6573792/3600=approx 187kbyte/sec = 1497kbit/sec

so you do the following
(i assume your audio track is in the required form

mencoder -oac copy -ovc lavc -lacopts vcodec=mpeg4:vhq:vbitrate=1497
infile.avi -o outfile.avi


hope this helps

if still not clear, reply and i'll try to help

btw. by those calculations i'm never sure where do you have to multiply
by 1000 and where by 1024, so those numbers can be wrong

and of course the resulting file won't ever be exactly that long.. there
can be +-1-2mbyte ( or more ) difference.

bye,
gabor

On Wed, Aug 07, 2002 at 11:18:51AM -0700, Steven M. Schultz wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> > From: Arpi <arpi at thot.banki.hu>
> > 
> > hmm? you use fixed bitrate - and filesize depends only on bitrate, so why
> > should it be different? quality and cpu usage will differ for IP and IPB,
> > but the file size won't unless you change bitrate...
> 
> 	I thought 'vbitrate' set the desired maximum limit - and that the
> 	actual bitrate was variable (VBR).   It was a surprise to find such a
> 	small difference between the B and non-B cases - that's all.
> 
> 	Is the lavc encoding VBR or CBR?   If it's CBR then yes  I understand
> 	the filesize being constant and depending only on the bitrate.   
> 
> 	Thanks.
> 
> 	Steven Schultz
> 	sms at 2bsd.com
> 
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