[FFmpeg-devel] AAC encoder questions

[Alex Converse]

On Fri, Apr 24, 2009 at 1:30 PM, Kostya <kostya.shishkov at gmail.com> wrote:
> On Fri, Apr 24, 2009 at 01:04:56PM -0400, Alex Converse wrote:
>> On Fri, Apr 24, 2009 at 9:34 AM, Kostya <kostya.shishkov at gmail.com> wrote:
>> > On Fri, Apr 24, 2009 at 03:51:13AM -0400, Alex Converse wrote:
>> >> On Fri, Apr 24, 2009 at 3:16 AM, Kostya <kostya.shishkov at gmail.com> wrote:
>> >> > On Fri, Apr 24, 2009 at 03:07:18AM -0400, Alex Converse wrote:
> [...]
>>
>> Trying to work through the logic of it:
>>
>> Normally we do t - pow(clip(floor(pow(t * Q, .75)+0.4504), 8191), 1.333)*IQ
>> the top case is a shortcut where we know that the clip will resolve to
>> 8191. (I'm also not sure why we are using 8192 up there, but that is a
>> separate issue. "The maximum allowed absolute amplitude for x_quant is
>> 8191.")
>
> That value is still < pow(8192, 4.0/3), so it resolves to 8191 after all.
>

It's fine for the comparison but (if I'm understanding the code
correctly) when subtracting it understates quantization error.