[FFmpeg-devel] Default dynamic range compression on AC3

Wiebe Cazemier wiebe at halfgaar.net
Thu Mar 26 15:51:02 CET 2015

----- Original Message -----
> From: "Zach Swena" <zcybercomputing at gmail.com>
> To: "FFmpeg development discussions and patches" <ffmpeg-devel at ffmpeg.org>
> Sent: Thursday, 26 March, 2015 3:34:22 PM
> Subject: Re: [FFmpeg-devel] Default dynamic range compression on AC3
> Something to keep in mind, AC3 is a broadcast format, so it makes sense to
> have range compression built in because many listeners are viewing on TV
> sets with limited range capabilities.  I wasn't aware of this option, but
> will probably end up using it for a program I am making.  I don't care
> about the default value, as long as I can change it and the feature and
> default value get proper documentation.  That is just a bit of background
> on why the AC3 spec has this feature.  Theoretically it should be turned
> off at the decoder if connected to proper speakers though.

This was brought up in the Kodi discussion as well. I haven't answered there (yet), but it has been my experience that TV networks already apply a whole bunch of compression on the stream itself, outside of the meta data. Disabling DRC doesn't help in preventing horrible compressed sound quality.

In any case, the use of AC3 for broadcasting shouldn't mean that DRC is on by default. Settop etc boxes that want this should turn it on themselves, not rely on a library that performs it with the developer using ffmpeg not even knowing about the existence of it. And the developers that do know, will simply set drc_scale.

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