[MEncoder-users] lavc or xvid

[Loren Merritt]

On Tue, 4 Sep 2007, RC wrote:
> On Tue, 4 Sep 2007, Phil Ehrens wrote:
>
>> Eek! nr=300?! Alright, I admit it... I reported the same thing
>> once (or twice). If the source genuinely has significant gaussian
>> noise, nr=300 can perform miracles... HOWEVER, if you are starting
>> with good clean source (like a well-made dvd), nr=10 to nr=30 is
>> more realistic.
>
> Almost every DVD I've seen has significant noise, and nr=300 helps a
> lot (and I've done several visual and PSNR tests to demonstrate that).

Are you really saying that nr=300 improved PSNR? It intentionally changes 
the content, so it intentionally reduces PSNR if you compare input to 
reconstructed output. Which is not to say that it's impossible: maybe you 
save so many bits by removing the noise that when those bits are 
reallocated to other regions of the movie they make up for the earlier 
PSNR loss.

>> These numbers are for 2-pass encodes. If you are doing single-pass
>> encodes, hqdn3d will behave much more sanely than nr. But if you
>> are doing multi-pass, nr will be better on all live action. Anime
>> seems to really love hqdn3d, however.

Interesting. The only difference between 1 and 2pass I can think of that 
might cause that is that 2pass allocates bits as a function of bits (i.e. 
magnitude of quantized DCT coefficients), while 1pass allocates bits as a 
function of SSD. DCT coefficients have passed through nr, while SSD 
hasn't. So scenes with little content but much noise will be allocated 
lots of bits in 1pass nr, but not in 2pass nr nor 1pass hqdn3d.

> Unless it's extremely noisy material, I wouldn't use hqdn3d at all. With
> default values, it causes blockiness, fades color, and leaves a very
> noticable trail behind objects in motion.

hqdn3d doesn't have any block structure at all, so the only possible way 
it could cause blocking is if your video was already blocky but hidden 
behind all the noise, and hqdn3d just removed the noise.

--Loren Merritt