[vdr] Re: Mplayer-plugin output blocky..

[Ari Huttunen <Ari.Huttunen@f-secure.com>]

Patrick Cernko wrote:
> Also sprach Ari Huttunen zu "02.12.2003 14:21" Anno Domini:
> > I think having a qmax should limit quantization in the most difficult
> > scenes, and forces the kbit/s value there to a higher value. I'm not
> > exactly
> > sure, though, it's so hard to get good specifications about the command
> > line arguments for these tools.
>
> That's right! the man-page for ffmpeg is quiet short there. mencoder's
> man-page tells some more:
>
>        vqmax=<1-31>
>               maximum quantizer (pass 1/2) 10-31 should be a sane range
>               (default: 31)
>
> I'm not sure, if this is the same quatization as I mentioned.
> Please try encoding with the default. I never set this when I used
> ffmpeg for encoding, so I always implicitly used the default.
OK, there's definitely something there that I don't get, but no matter.
I tried encoding without limiting that quantizer and without the 4mv too.
I also tried it via encoder/lavc, with various options or not, like
filtering, quarterpels, etc. I couldn't try divx4 in mencoder since
that wasn't seemingly installed, and I didn't feel like recompiling again.

In the end, the only thing that had any real noticable difference was
the bit rate. 1500 kbit/s looked sort of bad, 1800 kbit/s had noticable
macroblock visibility, and 2500 kbit/s was only marginally better than
1800 kbit/s. And I think that by using mencoder and not ffmpeg directly
I got slightly better results.

Still, I don't think the encoder is necessarily bad. I just think it uses
all those extra bits to enhance the part of the picture that I *don't* look at,
or for other scenes. (I don't know for how long a time period a 2-pass encoder
can allocate those kbit/s.) It's not like the overall quality of all these
recordings wouldn't be generally good, since it is.

I do think this problem would be better solved by an output filter that would
somehow smooth out the macroblock boundaries when decoding. I believe this is
called a deblocking filter. I did try to apply it when playing it with
mplayer-plugin, but I apparently failed because it had no effect. Thus, my
suspicion that the MPEG-1 phase re-introduced those boundaries due to
insufficient bandwidth.

> > > Overall, I would suggest, to leave as most options as possible at their
> > > default values, which most often are the best choise for standard tasks.
> > > This is also true for other applications like mencoder!
> >
> > That's not compatible with the basic Linux ideology :-).
>
> I don't understand that. Is it better to specify all options explicitly,
> e.g.
>
> boot: linux vga=normal root=/dev/hda1 ...
>
> :-)
No, I meant that if I would be happy with the stuff as it came out of
the box, my Shuttle would still be noisy as hell, I would still be using
the lousy TV-application Technotrend wrote, etc.

Besides, both ffmpeg and mencoder have defaults that are pretty much useless
for my purposes. They may work for somebody who wants highly compressed
video for web streaming, or something.

Ari

--
Everything is not as bad as it seems. <Poolzmaiden>



--
Info:
To unsubscribe send a mail to ecartis@linuxtv.org with "unsubscribe vdr" as subject.