[flac-dev] Flac multi channel

Brian Willoughby brianw at audiobanshee.com
Sat Jan 28 06:37:10 UTC 2017

Don't overlook the FLAC in Ogg container solution. That's established as a standard for some time now, as far as I know, and would probably be better than a new, proprietary multi mono bundle. I haven't used it myself, but people have been talking about it for a while, and I believe that some "FLAC" users are actually working with FLAC in Ogg container files.

Brian Willoughby

On Jan 27, 2017, at 12:55 AM, Olivier Tristan <o.tristan at uvi.net> wrote:
> Thanks everybody for their answer.
> This is quite unfortunate for me, but hey, that's life.
> I will probably end up doing some multi mono bundle similar to what Protools did back in the days with its .L .R files
> Le 26/01/2017 à 18:58, Martin Leese a écrit :
>> Federico Miyara wrote:
>> ...
>>> The file format allows some unused fields for future use, such as the
>>> padding block. It could include a flag to indicate a change in the
>>> format adding one more streaminfo byte which would allow up to 256
>>> channels (actually, 256 + 8), or it could trigger a new byte when 11111111.
>>> There is also an invalid block identifier (127) which could be used with
>>> the same purpose.
>> The problem isn't *just* the 3-bit field used for
>> the number of channels.  As Brian Willoughby
>> explained:
>> ...
>>>> As you cram more channels into a block, you get fewer samples per block for
>>>> each individual channel. There simply isn't any advantage to having lots of
>>>> channels in a single stream.
>>>> I believe that Ogg allows you to create a file that interleaves multiple
>>>> FLAC files.
>> Perhaps comparing FLAC with the Ogg
>> container and Vorbis codec will aid
>> understanding.
>> With Ogg, different streams can be either
>> chained (sequential) or grouped
>> (parallel/interleaved).  Typically, metadata
>> streams would be chained (so they appear
>> before any audio data) and audio streams
>> would be grouped.
>> Within a single FLAC stream the audio is
>> split into blocks which are grouped.  But within
>> each block the eight channels are chained.
>> This makes sense with a maximum of only
>> eight channels.  Within a Vorbis stream the
>> audio is split into frames which are grouped.
>> Because a Vorbis stream can contain up to
>> 256 channels, within each frame the channels
>> are also grouped.
>> So the maximum of eight channels is really
>> embedded into the FLAC standard.  To change
>> this would require a whole new standard (or
>> the use of multiple grouped FLAC streams in
>> an Ogg container).
>> Regards,
>> Martin

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