[FFmpeg-devel] [GSoC] [PATCH 2/2] mlpenc: Working MLP/TrueHD encoder

Jai Luthra me at jailuthra.in
Sun Sep 18 08:22:02 EEST 2016

On Sat, Sep 17, 2016 at 05:07:28PM +0100, Andy Furniss wrote:
> Nice work, this is just a sort of related question really from a user
> who hasn't taken any notice of TrueHD for a few years.
> Last I looked I couldn't find much in the way of specs for TrueHD and
> noticed that the Decoder didn't have anything related to dynamic range
> control.
> Is there more info about now?
> IIRC testing decoder - (depending on content) for downmix or 2 channel
> sub stream the absence of DRC was a bit of a show stopper in that full
> range can be way too much. The AC3 version of course did have DRC meta
> and ffmpeg would correctly fully apply it for downmix, so for a stereo
> listener like me AC3 = good, TrueHD (or DTS) = bad.

The proprietary suite for TrueHD does support dynamic range compression, but I'm
unsure if (and where) the metadata for DRC is present in the bitstream.

The bitstream isn't fully reversed yet, just enough to get things working. I
think this is a very useful feature for downmixed substream to sound good, so
I'll try to figure it out in my spare time.



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