[FFmpeg-devel] [PATCH/RFC] set qscale_type for MPEG-4

[Michael Niedermayer]

On Wed, Feb 03, 2010 at 07:12:46PM +0100, Reimar D?ffinger wrote:
> On Wed, Feb 03, 2010 at 01:16:02AM +0100, Michael Niedermayer wrote:
> > On Tue, Feb 02, 2010 at 11:54:26PM +0100, Reimar D?ffinger wrote:
> > > Hello,
> > > I have no idea if this actually makes sense, but MPlayer's -vf fspp seems to
> > > look a lot better with it for me - no idea if MPEG-4 qscale is more similar
> > > to MPEG-2 or MPEG-1.
> > 
> > mpeg4 has 2 quantizer types, one matches h263 one mpeg2 with a factor of 2
> > difference in qscale
> 
> So in neither case the patch I made makes any sense?
> Or is the H.263 one somewhat close to MPEG-2?

why dont you read the code?
get_qscale()
mpeg1_decode_block_inter()
mpeg2_decode_block_non_intra()

mpeg4_decode_block()


> 
> > mpeg1 and 2 depend on the used quant matrixes as well, thus make tripple sure
> > your test files use the default matrixes and mpeg4 uses h263 style
> 
> The MPEG-4 used H.263 style, quantizer 15. And with fspp and spp the
> picture looked far worse than without while with the patch it gave
> a decent improvement (particularly any areas of large, identical colour).

also keep in mind that a encoder might behave different from what one
expects that is it might create blockier output than another at the same
quantizer.
i guess to figure out what is wrong you could just encode your own
video at constant quantizer and then test which constant with spp looks
best. Also you could add a user settable factor to spp so people can
adjust the strength ...

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Old school: Use the lowest level language in which you can solve the problem
            conveniently.
New school: Use the highest level language in which the latest supercomputer
            can solve the problem without the user falling asleep waiting.
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