[FFmpeg-devel] [PATCH v2 6/8] aaccoder: add a new perceptual noise substitution implementation

Michael Niedermayer michaelni at gmx.at
Sun Jul 5 16:52:44 CEST 2015

On Fri, Jul 03, 2015 at 12:07:42AM -0300, Claudio Freire wrote:
> On Thu, Jul 2, 2015 at 3:13 PM, Rostislav Pehlivanov
> <atomnuker at gmail.com> wrote:
> > This commit finalizes the PNS implementation previously added to the encoder by moving it to a seperate function search_for_pns() and thus making it coder-generic. This new implementation makes use of the spread field of the psy bands and the lambda quality feedback paremeter. The spread of the spectrum in a band prevents PNS from being used excessively and thus preserve more phase information in high frequencies.  The lambda parameter allows the number of PNS-marked bands to vary based on the lambda parameter and the amount of bits available, making better choices on which bands are to be marked as noise. Comparisons with the previous PNS implementation can be found here: https://trac.ffmpeg.org/attachment/wiki/Encode/AAC/
> >
> > This is V2 of the patch, the changes from the previous version being that this version uses the new band->spread metric from aacpsy and normalizes the energy using the group size. These changes were suggested by Claudio Freire on the mailing list. Another change is the use of lambda to alter the frequency threshold. This change makes the actual threshold frequencies vary between +-2Khz of what's specified, depending on frame encoding performance.
> LGTM. I probably should mention I already thoroughly tested a WIP
> version of the patch (which looks identical).



Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Into a blind darkness they enter who follow after the Ignorance,
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to the Knowledge alone. -- Isha Upanishad
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