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

Michael Niedermayer michaelni at gmx.at
Mon Mar 30 16:28:24 CEST 2015

On Mon, Mar 30, 2015 at 11:37:10AM +0200, Wiebe Cazemier wrote:
> ----- Original Message -----
> > From: "Kieran Kunhya" <kierank at obe.tv>
> > To: "Wiebe Cazemier" <wiebe at halfgaar.net>
> > Sent: Monday, 30 March, 2015 10:47:49 AM
> > Subject: Re: [FFmpeg-devel] [PATCH] Dolby Digital dynamic range compression (drc_scale) is now 0 by default
> > >>
> > >> It is not an option and I quote ETSI 102 366:
> > >>
> > >> "Therefore, the AC-3 decoder shall, by default, implement the
> > >> compression characteristic indicated by the dynrng values in the data
> > >> stream. AC-3 decoders may optionally allow listener control over the
> > >> use of the dynrng values, so that the listener may select full or
> > >> partial dynamic range reproduction."
> > >>
> > >> If an application doesn't want to expose drc settings then that's
> > >> their problem. FFmpeg does the right thing and lets you turn it off if
> > >> you wish.
> > >>
> > >> Kieran
> > >>
> > >
> > > (can you reply-all, so that your reply goes to the list?)
> > >
> > > If you say "it's not an option", that's putting it harder than the spec
> > > say. Dolby engineers never meant AC3 audio to be played compressed
> > > everywhere, and that's what we're seeing happening.
> > >
> > > Also, I feel that the word 'decoder' in your quote is written in a time
> > > where it had a different context and that quote has to be interpreted that
> > > way. Open source software libraries weren't available at that point, and a
> > > decoder was a piece of hardware, or a chip embedded in something. Sure,
> > > you don't have to allow the user to control it when you embed an AC3
> > > decoder in your budget TV so ATSC demanding that you do would be silly
> > > here, but all high end receivers I know, do allow you to set the option.
> > > Now that we do have a library that people can use, an honest mistake to
> > > forget to implement it turns into something that they probably didn't
> > > intend. As proven by the Kodi developer denying that they applied DRC.
> > >
> > > I think we have to consider user experience, and it's great when they can
> > > control it, but we're getting the situation where everybody gets it (yet
> > > only for AC3), whether they want to or not. That automatically crosses off
> > > Kodi and VLC (for example) for use in high quality sound reproduction. And
> > > the bad thing is, they may not even know it...
> > 
> > It's the complete opposite - most people are watching on laptop
> > speakers without the dynamic range you have in your setup. FFmpeg lets
> > you turn it off and it's the fault of the player for not exposing
> > that.
> What about those people playing AAC, which is the majority currently.
> In any case, I made my point. How do we proceed? I have no idea who is in charge of what, and how the decision making process goes in ffmpeg development.

Generally decissions are made based on consensus or absence of
objections. If that doesnt work there should be a maintainer for the
specific part of the code. Iam not sure AC3 in FFmpeg does have a
maintainer, justin is listed in MAINTAINERs but iam not sure if justin
still (wants) to maintain ac3 in FFmpeg.
so considering that kierank and andy seem to object to this patch
someone should
1. ask justin if he is still MAINTAINING AC3 in FFmpeg
2a. if yes, ask him what to do
2b. if no send a patch to update the MAINTAINERs file and if noone
    else wants to maintain AC3 the decission would proably fall onto
    me, unless theres something resembling a consensus by then

also independant of this, its probably a good idea if we make our
users more aware of the drc_scale option. A news entry and or some
mention in the next release notes is probably a good idea
patches in that direction are welcome



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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