[MEncoder-users] encoding technical question

[Philippe MONROUX]

De (from) (von) <jimht at shaw.ca> :

> 1)  None of  those dimensions  are evenly  divisible by  16  so your
> compression efficiency will suffer.

I know but It was just an example. The question is not about resolution.

> 2) Unless I am very much  mistaken, CQ will not give you predictable
> file sizes, since it will  use whatever bitrate is needed to provide
> the quality specified., so the  basis of your question is flawed. In
> my experience, the only way to achieve a fixed final file size is to
> do two pass encoding specifying bitrate, not CQ or CR.

Sure but, read in doc :

resolution x CQ = (bitrate x 1000)/25 (if 25 fps)

In my example :

600x200x0.10=12000
450x150x0.177=11947.5

> 3) I am  assuming that the underlying question is,  "is it better to
> have more  pixels at a  lower quality, or  fewer pixels at  a higher
> quality?"

Sure (perhaps my question wasn't clear...)
 
> In reality  the answer is bit  more complex. Smaller  images tend to
> have higher entropy (each pixel  is more likely to be different from
> its neighbors) and therefore require slightly more bits per pixel to
> encode.   Bitrate  requirements do  not  scale  linearly with  image
> resolution.

> These are just my opinions, based  on my experience, so take em with
> a grain of salt.

-- 
mxph