[XviD-devel] Xvid v's H.264/AVC

[Christoph Lampert]

On Tue, 6 Jul 2004, Hans K. Rosbach wrote:
> I assume that this is not as valid when re-encoded to lower resolution
> and/or
> with some kind of filtering before re-encoding..?

You are right, possibly not. Although the resizing filters might 
have to somehow smooth the image as well to avoid aliasing. 
What kind of filtering did you think of? 

gruel

P.S. I might have stated it wrong in the original posting: It's not that 
MPEG-4 Qpel is bad at encoding MPEG-2 material or anything. It's just that 
MPEG-4 Hpel is extremely good at it, otherwise it would be impossible to 
reduce a 8 Mbps to less than 2 Mbps with almost no visual quality loss. 
QPel doesn't make improve it any further. 
But this is also a problem of measuring performance, because a high PSNR 
value (which many people take as "good quality") here only means that the 
MPEG-4 result is close to MPEG-2's output including all visual artefacts 
that that might have had. 
In fact, some people say that Qpel images look better than Hpel ones, even 
at same PSNR. 

For input material that wasn't recompressed (as little as there is 
available), much higher bitrates are needed to get similar PSNR numbers.