[MEncoder-users] converting and subtitle questions

[Erik Slagter]

Jorge Peixoto de Morais Neto wrote:

> a) H.264 for low-bitrate encoding when you have little storage
> b) MPEG-4 part 2 for high-bitrate encoding when you need little CPU usage.

Myself I am convinced that h264 is always superior to mpeg4-2, given the 
right options.

I found an article when googling (about something else) that explains 
why h264 sometimes looks "washed out" compared to mpeg4-2 clips. They 
state that actually the h264 picture is "better" (more truthful to the 
original) but the deblocking filter masks blocky artifacts that in it's 
turn tend to mask missing details. So you're actually masking the 
masking ;-). It sounds a bit like sharpening and denoising filters in 
photo camera's. Once you're used to them, you need to get used to the 
"clean" pictures shot with a more expensive camera. At first sight it 
looks like it lacks details (of course you turn off completely the 
sharpening and denoising in the camera itself) and then when you apply 
just a very mild sharpening, suddenly the picture is stunning. You just 
don't get the details that aren't there ;-)

> My remarks:
> a) x264's constant quality (crf) option is excellent. 

I also like that one. One disadvantage is that is completely ignores any 
buffer requirements imposed by the device you're going to play the video 
on. If your device doesn't care, you're fine.

> It is hard to understand what lmin and lmax exactly do. I have studied
> lagrange multipliers, but I cannot understand what lmin and lmax
> really do.

Seconded. I have been staring at these options (including the source) 
for hours, but it doesn't get any clearer. Also the docs do not help.

One time even Michael has had a go at explaining it (in two 
sentences...) but it didn't quite help. It looks like lmin and lmax are 
the counterparts of qmin and qmax, but then for encoding at a target 
bitrate and vbv. It seems though you still can use qmin and qmax then...

> My specific requirement is to capture TV at (of course) realtime with
> constant quality. The quality should probably be quite high, so I can
> later (if I decide so) reencode with a super-high encoding efficiency
> (probably H.264).

I have done this for year, until I bought me a satellite dish :-)

> b) H.264's crf option does not really yield 'constant' quality. The
> quality varies a lot; in my case, the intro looked bad, probably
> because it has lots of motion. While I don't care about the intro of
> my cartoons, I wouldn't like a, say, war movie to have bad looking
> high motion scenes. Can the Mencoder guys fix this?

No, the x264 guys need to fix this :-)

Although don't put your money on bitrate control, the computer cannot 
ever exactly "see" what you see.