Michael,
I haven't been so active in mjpeg tools stuff in the past few months
and left my work in an unfinished state.
However, I had been working on a more useful version of the
'lav2mpeg' tool. One of the things I wanted to add was a "--fit"
option, that would function as follows:
- if CBR, calculate appropriate bitrate and use that.
- if VBR, calculate a guess on the maximum bitrate, based on what
CBR would fit (was using 1.2 * CBR). then try -q values to
mpeg2enc over a subset of the video ( say 2 minutes taken from
random places in the video, in 15 second or so clips). Get the
output size of that, and project out to full length. if the
projected size was going to be more than the value given to
"--fit", then try a lower "-q" value, if smaller, try a larger
value until you have one you think will work.
- if it ends up not working, consult a variable as to whether or
not thats ok. if not ok, then respin the entire encode with a
lower -q and or lower max bitrate.
The process is wastefull and not perfect, but if it can be taylored
to work, then the only real waste to the end user is in the effective
FPS.
I had some shell script code that would calculate all the needed
bitrates and kick out an edit list file that was of the desired length,
but never got to tying it all together or testing it.
If your'e interested in what i have i can fish it up.
Scott
On Sat, 25 Jan 2003, michael wrote:
>
> Can anyone point me at a source of information on calculating bitrates for
> transcoding to svcd with mjpeg tools. Or even a calculator that runs under
> linux. At present I transcode my captured video with a best guess bitrate
> and then modify the bitrate accordingly to fit it on 1 or more 80 min cd-r's.
>
> My attempts so far result in bitrates that don't work in the real world.
> Guess the formulas I constructed are based on insufficient/inaccurate/not
> fully grocked data.
>
> -oOo-
>
> Not that it's relevant: Capture is with either lavrecord from a buz or, more
> recently, using a digital8 camcorder to transcode analogue to video and
> dvgrab. All that talk about Canopus boxes made me jealous so I figured out
> that my camcorder ought to be able to do the same and with a little play it
> did.
>
> I'm keeping the buz in my machine for now but the quality and rock solid
> reliability means I'm using dv almost exclusively.
>
>
> Thanks,
>
>
> Michael.
>
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