How does boolean entropy coder works in VP8?

[Ahlucard]

I can't find any useful reference.
can u help me?

:thanks:

[Dark Shikari]

It's a dead-simple arithmetic coder -- there's not much to explain. The code is almost identical to x264's, except that it's multiply-driven instead of table-driven.

[Ahlucard]

I know what u mean.
Infact, what i want to know is:
While VP8 is using multiply-driven entropy coder , there must be a "Probability Table".
I can't understand how this "Probability Table" use in entropy coder and especially how it updata.

[foxyshadis]

You just want to know how Arithmetic coding works in general? Start with http://en.wikipedia.org/wiki/Arithmetic_coding.

[Ahlucard]

I know how Arithmetic coding works in general.
In fact, i am making a detailed compare of h.264 and VP8 .
I found that their entroy coder is quite different ,
but i can't understand how VP8's entropy coder works in detailed by reading its spec. (Especially at how the probability table update in every frame)
So, if somebody know that, please share the experience with me. Thank you very much.

[Goldfist]

Unlike H.264 CABAC, which updates parobability every time after bool is coded, the probability tables of VP8 can only be updated in frame header.
That is why people said that VP8 entropy has less adaptive than H.264 because the former can only updates them at "frame-level".
You can find the detail about how to update the prob. at the end of VP8 spec. document.