[MPlayer-dev-eng] 2 pass encoding - need explanation

[D Richard Felker III]

On Sat, Feb 22, 2003 at 08:39:57PM +0100, Jonas Jermann wrote:
> Hi
> 
> On Sat, Feb 22, 2003 at 04:23:55PM -0500, D Richard Felker III wrote:
> > BTW, you should try with vqscale=2 on the first pass and see if that
> > works well, rather than vqscale=5. The latter will encode the whole
> > first pass at very low quality so it probably won't estimate
> > complexity well.
> 
> What about the encoding speed? Someone told me that it is the 
> same for each quantizer (I doubt it). And what about quant=1? I 

Encoding speed should not be affected by quantizer directly. Of
course, the quantizer will affect motion estimation some, so it may
change a little, but shouldn't change too much.

> heard it shouldn't be used. Does this apply to 1. pass too?

It's probably safe to use q=1, but there's not much benefit and it can
actually waste bits and reduce the quality if you use vqmin=1 with
rate control.

> And do small differences off quantizers matter for the 
> estimation anyway? It doesn't encode yet, so my common sense tells 
> me it will almost be the same result.

Yes it does encode. The first pass encodes *and* collects statistics
from the encode to use in better distributing bits/adjusting quantizer
in the second pass. So it's beneficial for the stats to be good.

Rich