[FFmpeg-soc] [PATCH] AACENC: Fix HCB selection

[Kostya]

On Fri, May 29, 2009 at 12:41:10PM -0400, Alex Converse wrote:
> On Fri, May 29, 2009 at 12:00 AM, Kostya <kostya.shishkov at gmail.com> wrote:
> >
> > On Thu, May 28, 2009 at 05:53:51PM -0400, Alex Converse wrote:
> > > Hi,
> > >
> > > This patch seems to vastly improve HCB selection in the AAC encoder.
> > > The screenshot demonstrates its results. (out-1 is before, out-2 is
> > > after, chunk is input)
> > >
> > > Regards,
> > > Alex Converse
> >
> > I believe it does, the question is why?
> > I see two changes - in codebook selection (which does the same thing
> > on the first glance) and in its traversal.
> 
> The first chunk of the new code iterates over each stage (swb) and
> figures out the total cost to get to each state (hcb) by staying in
> that state from the previous stage and by transitioning to that state
> from the lowest cost state of the previous stage.
> 
> The old code seems to also iterate over each chunk and figures out the
> cost to get to each state (hcb) by staying in that state from the
> previous stage then it seems to compute, as it's alternate cost, the
> cost of navigating to that state in the previous stage plus the cost
> of the lowest cost stage of *this state* (including run increase
> penalties but not the navigation cost). If that cost is lower, we mark
> it as a transition from the lowest cost state this stage. That second
> quantity and how it is handled doesn't seem to make a lot of sense.

Indeed, so that was my error.
 
> > Does the second part fix some bug, simple ineffectiveness or simply
> > needed for changed codebook selection scheme?
> >
> 
> The second part simply walks us back to the proper place to look at
> the previous state on a run > 1. It's hard to evaluate on it's own
> since the old code it interfaced with doesn't make a lot of sense.

Apply as single patch then.

> [...]
> 
> --Alex