[MEncoder-users] encoding technical question

[Jorge Peixoto de Morais Neto]

> In http://www.mplayerhq.hu/DOCS/tech/encoding-tips.txt you can read:
> < 0.10: don't do it. Please. I beg you!
> < 0.15: It will look bad.
> < 0.20: You will notice blocks, but it will look ok.
> < 0.25: It will look really good.
>  > 0.25: It won't really improve visually.
>  > 0.30: Don't do that either - try a bigger resolution instead.
This seems very radical. Perhaps this is for an outdated encoding technology.
I have obtained good video quality for a 480x276 25 fps video at 288
kbps. This is about 0.087 bits per pixel. There are blocks, but most
of the time they aren't very serious.
Note: This encoding was done some time ago; I don't remember why I
left the height as 276 instead of cropping to 272 (which is a multiple
of 16).
I have used the options
lavcopts=keyint=300:vmax_b_frames=1:vb_strategy=1:b_sensitivity=10:mbd=2:trell=yes:v4mv=yes:cbp=yes:preme=2:mbcmp=3:vqcomp=0.6:predia=3:dia=3:mv0=yes

>
> You formulas just calculate the resolution, based on the BPP you want
> (quality) and the bitrate you wish to spend (size), while keeping an eye
> on video and pixel aspect ratios.
>
> This is a little problematic, because clearly quality and filesize _must
> be_ conflicting properties! When keeping the original resolution, you
> can only choose one of them (as you somehow do with constant
> quantizer/VBR (choosing quality) opposed to constant bitrate/CBR/ABR
> (choosing size)), the other one then depends on the first one.
>
> The author finds a way out of this dilemma by varying the resolution. Of
> course this works, but a lower resolution also means less detail, very
> much like higher compression. So in the end it boils down to filesize
> versus quality, again.
>
> As for your original question: I would suspect that 600x200 with CQ=0.10
> will look just as bad as 450x150 with CQ=0.177 _on average_ depending on
> the movie characteristics).
> The difference is, that the latter will have less artifacts! Both will
> lose about the same amount of detail (the first because of higher
> quantizers, cutting off more of the high frequencies, the second because
> of the sampling theorem, which just "forgets" about the high frequencies
> and leaves more bits for encoding the low ones).
> It's just that you don't see the lost frequencies on nicely (= low pass
> filtered) scaled down images, whereas you DO see blocking artifacts on
> images with quantizers too large!
I don't like scaling the video down. I see this as the victory of
aesthetics (absence of artifacts) over functionality (visual detail).
Please, at least try encoding the video at its original resolution and
see if you like the results. ***Do not*** automatically scale the
video down according to some internet guy's formula.
-- 
Software is like sex: it is better when it is free - Linus Torvalds