[FFmpeg-devel] [PATCH] AAC Encoder: clipping avoidance

[Claudio Freire]

On Mon, Jul 20, 2015 at 11:39 PM, Claudio Freire <klaussfreire at gmail.com> wrote:
> On Fri, Jul 17, 2015 at 8:42 PM, Michael Niedermayer
> <michael at niedermayer.cc> wrote:
>>> If you mean a transition in time, I don't think it makes any
>>> difference. 0.95 is a ~0.5db change in intensity, which ought to be
>>> inaudible, and windowing will already take care to make the transition
>>> smooth. And the logic wouldn't be completely free either to ramp
>>> gradually, as it would have to ramp fully to 0.95 by the time it
>>> reaches the first window marked as clipping hazard, and it could very
>>> well be the frist window.
>>
>> what i meant was that whatever condition is used to hard switch
>> between 1.0 and 0.95 could be rather a soft transition that is
>> for example
>> insteda of
>> if (x > 0.0) f = 0.95
>>
>> something like
>> if (x > 0.0 && x<1.0) f = 1.0 + (0.95 - 1.0)*x
>>
>> so theres no discontinuity in the transition
>
> Attached is a patch with something like that.
>
> 1. It measures per-window minimum clip avoidance factor
> 2. Computes a whole-frame factor (minimum of all)
> 3. Applies the clip avoidance factor to the whole frame (to make it
> smooth and almost linear, and avoid adding harmonic distortion).


Sorry, that one had trailing whitespace again.

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