[FFmpeg-devel] [GSoC] [PATCH 2/2] mlpenc: Working MLP/TrueHD encoder
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Sun Sep 18 12:56:37 EEST 2016
Jai Luthra wrote:
> 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
Thanks, it would be really good if the meta could be found even just for
the the decoder. I guess it would be a lot more complex for encode anyway.
I notice we both use the term downmix, maybe that's not quite the right
thing to say WRT substreams. I mean that in the sense that THD
substreams are AIUI the base and the higher channel counts are derived.
Which means the stereo mix can be different from what a downmix would
make. I've got a 7.1 speaker check sample somewhere and the stereo
substream has all the speakers at the same level, which is a nice
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