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

[Michael Niedermayer]

Hi

On Mon, Jul 27, 2015 at 07:28:35PM +0200, Michael Niedermayer wrote:
> On Mon, Jul 20, 2015 at 11:40:54PM -0300, Claudio Freire wrote:
> > 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.
> > 
> > Attached.
> 
> >  libavcodec/aac.h      |    4 +
> >  libavcodec/aaccoder.c |  108 ++++++++++++++++++++++++++++++++------------------
> >  libavcodec/aacenc.c   |   38 +++++++++++++++++
> >  libavcodec/aacenc.h   |    2 
> >  libavcodec/aacpsy.c   |   30 +++++++++++++
> >  libavcodec/psymodel.h |    1 
> >  tests/fate/aac.mak    |    4 -
> >  7 files changed, 145 insertions(+), 42 deletions(-)
> > fb3816accbd479ea10b2be6c104e28eee81ce743  0001-AAC-Encoder-clipping-avoidance.patch
> > From 57522de7c5fcdbef222c2425a4add6fa4528f0e7 Mon Sep 17 00:00:00 2001
> > From: Claudio Freire <klaussfreire at gmail.com>
> > Date: Mon, 20 Jul 2015 22:53:24 -0300
> > Subject: [PATCH] AAC Encoder: clipping avoidance
> 
> applied

it seems this breaks mips-qemu

see:
http://fate.ffmpeg.org/report.cgi?time=20150729171949&slot=mips-ubuntu-qemu-gcc-4.4

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

What does censorship reveal? It reveals fear. -- Julian Assange
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