[MEncoder-users] Compressing the photo camera Canon A610 video to mpeg4 at the best quality.

[Lennart Börjeson]

torsdag 21 september 2006 18:50 skrev Strong:
>
> Thank You. The following statement
>
> for V in 1: 3 3:qns=3
>
> should not be turned to
>
> for V in 1: 2 3:qns=3
>
> ?

In the beginning there was only two-pass mode, then the sequence was vpass=1 
follwed by vpass=2. "vpass=1" means "this is the first pass in two-pass mode" 
and "vpass=2" means "this is the final pass in two-pass mode". When multipass 
was introduced, the meaning of "vpass=2" couldn't easily be changed. So 
"vpass=3" DOES NOT mean "this is the third pass...", it means "this is any 
pass after the first in multipass mode".


>
> I did like this line very much:
> $ mencoder -oac copy -ovc lavc -lavcopts
> vcodec=mpeg4:vbitrate=4400:autoaspect=yes:v4mv=yes:trell=yes:mbd=2:vpass=$V
> -ffourcc DIVX
>

I have understood from postings on this list that it is prudent to always 
re-encode audio on all passes, so don't use -oac copy. Often when I've tried 
-oac copy the audio and video has gone out of sync.

> But a question arised: as my camera gives noisy video clips (the
> pixels around the object are moving around randomly) which
> codec parameter I should tune up to minimize that effect to save the
> basic object quality the most? I know there is smooth key but I would
> use it by codec as the quality unavoidably reduces.

There are many noise-reduction options in mencoder. You could use -vf 
hqdn3d=2:1:2 or something similar (look up the documentation and play around 
with the values), which is independent on the codec, or use a code-specific 
option like -lavcopts nr=500. Again, play around with the value.

Also note that specifying qns as I did in my example is very cpu intensive. It 
might do wonders on some clips but most of the time I can't notice the 
difference. I only use it as a last-ditch approach.

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