[FFmpeg-devel] Video codec design for very low-end decoder

Michael Niedermayer michael at niedermayer.cc
Mon Jan 7 18:42:58 EET 2019

On Mon, Jan 07, 2019 at 03:38:35PM +0200, Lauri Kasanen wrote:
> On Mon, 7 Jan 2019 13:44:56 +0100
> Michael Niedermayer <michael at niedermayer.cc> wrote:
> > > The modern approaches, DCT, FFT, wavelets and such transforms, are all
> > > likely too slow to decode.
> > 
> > you said it can do mpeg1 and xvid, these are DCT based
> > have you tried H.264 ? (i imagine that might with asm optimizations
> > and avoidance of more complex features like CABAC and the loop filter
> > work maybe, maybe not)
> > also if h.264 with everything disabled works maybe some features can
> > be turned on sometimes like the loop filter for key frames, that 
> > might then help compression ...
> > 
> > and beating an existing codec, while certainly possible might be hard
> According to a 2010 comparison
> https://keyj.emphy.de/video-encoder-comparison/
> x264 constrained baseline (everything off) takes something like 30%
> longer to decode vs xvid at the same rate. Probably more because that
> site used xvid's full features, while I used it "everything off".

constrained baseline is not "everything off"

> The issue with xvid simple and mpeg1 were that they were slightly too
> slow, and looked too bad. The platform does not have any SIMD, so I
> doubt asm optimizations will help much.

I would guess that with rare or odd architectures
compilers are not so good when it comes to generating efficient code.

I would not be surprised if someone who knows the target CPUs pipeline
and timings could beat the compiler by quite some amount.
This is one part where the amount of man hours needed is significant
of course. Would that be worth it, well its your project you have
to know what amount of work you are willing to do for this, 
i wouldnt do that work ;)

besides, why this low end chip ?

> Cinepak is almost 30 years old, surely it should be possible to match
> the decoding & quality, but at a 5x lower bitrate :P
> - Lauri
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Dictatorship naturally arises out of democracy, and the most aggravated
form of tyranny and slavery out of the most extreme liberty. -- Plato
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