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

[Alex Converse]

On Fri, May 29, 2009 at 1:17 PM, Kostya <kostya.shishkov at gmail.com> wrote:
> 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.
>

Applied

> [...]

--Alex