[MEncoder-users] encoding technical question

[James Hastings-Trew]

Philippe MONROUX wrote:
> Hi,
>
> Assuming I want a fixed size final file in a h264 encoding. 
>
> What are the criterion to choose between :
>
>      - XxY=600x200 with CQ=0.10
>      - XxY=450x150 with CQ=0.177... 
>
> which give (approximately) the same bitrate
>
> Thanks
>
>   
1) None of those dimensions are evenly divisible by 16 so your 
compression efficiency will suffer.
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.
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?" 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.