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<div class="moz-cite-prefix">Hi Aaron,<br>
<br>
I had some discussion and analysis regarding their coding part,
and there is a few percents to easily squeeze there (5-10%).<br>
In contrast to nasty CABAC scheme - start with binarization then
try to model these bits, Daala has very nice general scheme: <br>
send to coding part sequence of (ID, symbol),<br>
where symbol is from up to size 16 alphabet,<br>
each ID is statistically modeled as independent random variable -
hence ID itself contains both data type and context (like
neighborhood). <br>
<br>
However, they have a few inefficiencies:<br>
1) start each frame with flat uniform probability distribution
(this is the worst!),<br>
2) use approximated multi-symbol range coder:
<a class="moz-txt-link-freetext" href="https://people.xiph.org/~tterribe/tmp/StuiverMoffat98-%20Piecewise%20Integer%20Mapping%20for%20Arithmetic%20Coding.pdf">https://people.xiph.org/~tterribe/tmp/StuiverMoffat98-%20Piecewise%20Integer%20Mapping%20for%20Arithmetic%20Coding.pdf</a><br>
the cost of this approximation is 1-3% ratio loss for binary
alphabet: <a class="moz-txt-link-freetext" href="https://dl.dropboxusercontent.com/u/12405967/Moffat.nb">https://dl.dropboxusercontent.com/u/12405967/Moffat.nb</a><br>
3) use costly every symbol adaptation (mainly to handle the flat
initial distribution problem), but with <br>
freq[s] = count[s] / total<br>
poor type of adaptation: a symbol far in the past has the same
influence on the probability as the most recent symbols,<br>
4) use fixed adaptation rate.<br>
<br>
These can be improved by:<br>
1) Start with a probability distribution characteristic for a
given ID, for example a fixed parametric, eventually modified
somewhere in the file (better behaves in the beginning and allows
for more subtle adaptation),<br>
2) use an accurate entropy coder, like rANS in VP10,<br>
3) use adaptation with exponential forgetting to make recent
symbol more important, like <br>
for (int i = 1; i < m; i++) CDF[i] -= (CDF[i] - mixCDF[i])
>> rate;
<br>
where mixCDF is for the new part, can be tabled for symbol-wise
adaptation such that frequencies of not used symbol will drop to
the minimal nonzero frequency,<br>
4) Allow for varying adaptation rate - for example some ID use
more static probability distribution, for some it is beneficial to
allow encoder to choose one of a few possible adaptation rates.<br>
<br>
Kind regards,<br>
Jarek Duda<br>
<br>
<br>
<br>
On 16/04/24 05:36, Aaron Boxer wrote:<br>
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<div>Dear Daala-istas,<br>
<br>
</div>
I took a look at the PSNR and PSNR-HVS charts for daala vs
H.264 and H.265.<br>
</div>
May I ask at what PSNR value you would consider Daala to be
competitive with H.265 ? From the graph, it looks like you are
asymptotically matching H.264 quality, but there is still
significant difference with HEVC, and progress is flattening
out. <br>
<br>
</div>
<div>I don't mean to be that guy, but when do you think you will
be able to meet your project goal of meeting or beating HEVC
quality? I am asking because I think this is a great project,
and want to see it beating out the $$-driven competition.<br>
<br>
<br>
</div>
<div>Kind Regards,<br>
</div>
<div>Aaron Boxer<br>
<br>
</div>
<div><br>
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<pre class="moz-signature" cols="72">--
dr Jarosław Duda
Institute of Computer Science and Computer Mathematics,
Jagiellonian University, Cracow, Poland
<a class="moz-txt-link-freetext" href="http://th.if.uj.edu.pl/~dudaj/">http://th.if.uj.edu.pl/~dudaj/</a></pre>
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