Citando Marc Lavallée <m...@hacklava.net>:
Le 2018-07-29 à 03:08 PM, Stefan Schreiber a écrit :
Citando Marc Lavallée <m...@hacklava.net>:
Excerpt from https://xiph.org/flac/faq.html#general__channels :
"FLAC supports from 1 to 8 channels per stream. Channels are
only grouped in FLAC to take advantage of interchannel correlation
and to define common channel assignments (like stereo L/R, 5.1
surround, et cetera). When encoding a large number of independent
channels it is expected that they are coded separately and if
required, multiplexed together in a suitable container like Ogg or
Matroska."
Good info.
But this is a bit typical as an “answer”: HOW would you code many
channels separately in Flac (available sw to use etc.), and how to
multiplex into a “suitable container”?
Ok, no problem for anybody else... I am supposed to see! 😇
(https://xiph.org/flac/ogg_mapping.html
They don’t explain this at all, unless you take the faq answer as
a definition.)
Best,
Stefan
P.S.: They just have to extend (too) old definitions.
As Fons says, the limit is a limit (paraphrasing Theresa May) -
and not justified from a current perspective.
A few years ago I hacked the opusenc command line tool to encode
channels without inter-channel correlation, because the correlations
in the Opus codec were programmed for specific multi-channel
schemes, limited to 8 channels. The "joint stereo" MP3 mode is an
example of such a scheme, where channels are internally converted
before encoding (see:
https://en.wikipedia.org/wiki/Joint_%28audio_engineering%29).The
Opus codec now have an Ambisonics mode with new inter-channel
correlation schemes. I don't know if the fine Xiph developers can
"just" extend the definitions of FLAC, if a special Ambisonics mode
would be required, and to what extent the 8-channel limit (as a
limit) is a political issue. For the multiplexing of multiple
streams in a suitable container, it is left as an exercise. And if
the issue is just disk space, file compression softwares (zip, gzip,
etc) are still valid tools.
Marc
- - - - -
1. I believe that the opus encoders/decoders have always supported
more than 8 channels.
2. The next question is what ogg channel mapping and consequently
real-world browsers allow...
But in some sense the hack you did is known. (More complicated is
maybe to make it work...)
3. If they already plan to issue some ogg ambisonics standard (using
ogg opus of course) since at least 2016: You also need an associated
mastering standard, which would not change or compress any audio data.
Correct?
So what is “political” about extending the channel count of FLAC?
Compromise proposal:
4. So let’s maybe use .wav or .caf for the “mastering format”.
Microsoft and Apple already allow more than 8 channels... 🤔
Best,
Stefan
P.S.: “Joint stereo” you could classify as parametric coding.
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