[FFmpeg-devel] [Issue 664] [PATCH] Fix AAC PNS Scaling
Tue Oct 21 20:04:43 CEST 2008
On Tue, Oct 21, 2008 at 06:50:02PM +0100, Robert Swain wrote:
> 2008/10/21 Alex Converse <alex.converse at gmail.com>:
> > On Tue, Oct 21, 2008 at 1:29 PM, Alex Converse <alex.converse at gmail.com> wrote:
> >> On Tue, Sep 30, 2008 at 11:25 PM, Alex Converse <alex.converse at gmail.com> wrote:
> >>> The attached patch should fix AAC PNS scaling [Issue 664]. It will not
> >>> fix PNS conformance.
> >> Here is my understanding of the current situation:
> >> 1) PNS is part of the MPEG-4 AAC-LC object type
> >> 2) PNS is part of the most commonly used family of 14496-3sp4
> >> profiles, the AAC family of profiles (the AAC profile, the HE-AAC, and
> >> the HE-AACv2 profile)
> >> 3) PNS is *broken* in FFMPEG svn [Issue 664], *regardless of per band scaling*
> >> 4) (For better or worse) PNS requires per band scaling in the latest
> >> standard (ISO/IEC 14496-3:2005)
> >> 5) PNS is a low bitrate tool
> >> (<http://www.hydrogenaudio.org/forums/index.php?s=&showtopic=34652&view=findpost&p=305762>,
> >> <http://www.hydrogenaudio.org/forums/index.php?s=&showtopic=53340&view=findpost&p=478068>)
> >> 6) ffaac is enabled by default in FFmpeg
> >> It seems counterproductive to let this broken situation remain while
> >> arguing the merits of square roots and other normalization schemes.
> >> I propose we:
> >> A) Fix PNS using one sqrtf() per band (aac-pns-scale-v3.diff)
> > Apologies, I attached the reversed diff. The patch attached to this
> > message is what I actually propose.
> >> B) People interesting in a non-inner-most-loop optimal 1/sqrt can duke
> >> it out afterwards. Alternative normalization schemes (like
> >> pregenerating noise) can also be explored by interested parties
> >> This will allow users to immediately stop using broken PNS
> >> accidentally (6,1, 2, 3) while the computational hit of one sqrtf per
> >> band (A) should be mitigated by the decreased complexity in decoding a
> >> low bitrate stream (5).
> >> Thoughts?
> I'm happy with this patch.
then apply it, you are aac maintainer
or do you think one of my patch application monkeies will do it for you? ;)
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
If you really think that XML is the answer, then you definitly missunderstood
the question -- Attila Kinali
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