[MPlayer-dev-eng] mencoder problem

[Michael Niedermayer]

Hi

On Friday 17 May 2002 16:47, D Richard Felker III wrote:
[...]
> > i guess all frames are encoded with qscale=3
>
> It seems there are several issues at hand. AFAIK, lavc always enforces
> the qscale min/max unless the caller has specified fixed qscale, as
> the second pass of mencoder's external 2pass (-pass 2) does. This
> could be a good or a bad thing, but right now, lavc's handling of this
> situation is broken.
>
> For example, suppose I encode a file with lavc's internal 2pass and
> request qmin=3, qmax=12, bitrate=1000. On the first pass, the file
> comes out a lot smaller than it should, because lavc is "too good" and
> doesn't need that many bits for qscale=3 in most frames. Then, when it
> comes time for the second pass, lavc rescales the qscales to make more
> efficient use of the available bits. BUT, when it scales down the
> qscale for a frame below qmin, it seems to just truncate the scaledown
> to qmin, rather than going lower, and it doesn't return the excess
> bits gained by this truncation to be distributed over the more
> complicated frames that could benefit from these extra bits!
it does redistribute the bits, otherwise its a bug ...

>
> At least in the meantime until lavc's 2pass code is improved to deal
> with this situation, and perhaps in the longterm as well, it's
> probably desirable NOT to use qmin/max in the second pass of encoding.
> I propose the following possible solution, although I don't know if
> it's the best or most intuitive:
>
> In mencoder, have the default values for vqmin/vqmax be 0, which will
> mean initialize defaults based on pass number. For vpass 1, it would
> just initialize them with the old defaults that exist now. For vpass
> 2, it would initialize them to 1 and 31.
i doubt that would be good, why dont u just set vqmin=1 vqmax=31 for both 
pass 1 and 2 ?

[...]

Michael