[FFmpeg-devel] [PATCH] Dolby Digital dynamic range compression (drc_scale) is now 0 by default

Michael Niedermayer michaelni at gmx.at
Mon Mar 30 13:35:24 CEST 2015

On Mon, Mar 30, 2015 at 11:28:29AM +0100, Kieran Kunhya wrote:
> On 30 March 2015 at 11:24, madshi <madshi at gmail.com> wrote:
> > 2015-03-30 12:10 GMT+02:00 Kieran Kunhya <kierank at obe.tv>:
> >> We should have DRC enabled in AAC and other codecs
> >> if it's considered a normative part of the spec.
> >
> > So basically you do what the spec says regardless of whether it makes sense
> > or not?
> Yes,

for FFmpeg, this is not true.
ISO mpeg4 specified one way to do QPEL, but the reference
implementation did it the other way. Our decoder tries hard to figure
out which of the 2 was used on the encoder side and matches it when
IIRC the mpeg4 spec was changed to match the implementation at some
point then as well

Some mpeg4 encoders do the edge handling for MC wrong, we detect them
and match it in the decoder. That way the user sees a nice video
instead of one with minor or not so minor artifacts. We clearly
violate a normative part of the spec by displaying these videos
without artifacts

we also detect some ancient buggy version of x264 and decode that
different from what the spec would require to match what the encoder

the above examples are of course bug workarounds
but then there is no spec that says
"output video with a modified gamma compared to the encoder input
 unless the user override that" or does one ? 


> and we let power users change things from the API - I don't see
> why that's so hard.
> Kieran
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Concerning the gods, I have no means of knowing whether they exist or not
or of what sort they may be, because of the obscurity of the subject, and
the brevity of human life -- Protagoras
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