Re: [FFmpeg-devel] [PATCH] ffprobe/eac3/mlp/dca: add detection of spatial audio extensions

[Hendrik Leppkes <h.leppkes@gmail.com>]

On Thu, Feb 9, 2023 at 5:42 AM Marth64 <marth64@proxyid.net> wrote:
>
> Signed-off-by: Marth64 <marth64@proxyid.net>
> ---
> Adds detection of spatial/object-based audio extensions in E-AC-3,
> TrueHD, and DCA XLL (DTS). This includes Atmos, DTS:X, and IMAX formats.
> Please let me know what I could improve, I'm learning still.
> Thank you.
>

The detection itself seems fine to me, however we should talk about
how the presence is communicated back to the user.

A new flag in AVCodecContext goes against a variety of designs we try
to avoid - namely having codec-specific things in a global struct, as
well as having only one value, rather then per-frame values.

So options that present themself to me:
(a) Use "profile". At least for DTS that would fit quite nicely, as it
already has profiles, and it seems like a logical extension. TrueHD
and eac3 do not have profiles, but it might still be sensible to put
it there. The advantage here is that it also automatically is conveyed
in AVCodecParameters after avformat opens a stream, so the information
is available early and lets players decide how to handle the stream.
(b) Use per-frame side data. The early-availability advantage is not
present here, so its not my favorite. side-data could be used in the
future to transport the actual object metadata, if needed.

So from where I'm standing we should maybe define profiles to use for
these. In the past profiles were at least suggested for TrueHD Atmos
before, but there were some objections, so maybe a good time to
revisit and see where we go from here.

- Hendrik
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