Vorbis dev - Jul 2001 - Comment Tag for Multichannel Streams

Hallo,

the specification in vorbis/doc proposes a set of comment tags, but I think
there's one missing for multichannel configurations. There should be a value
for
mapping the individual channels to spatial locations. Lets assume a Vorbis
stream contains 4 channels, two front channels and two back channels, then the
corresponding comment value could be

CHANNELS=FRONT_LEFT,FRONT_RIGHT,BACK_LEFT,BACK_RIGHT

where the first value corresponds to channel 0, the second to 1 and so on.

Using the following values for channel mappings would allow a 1:1 translation
with DirectShow:

FRONT_LEFT
FRONT_RIGHT
FRONT_CENTER
LOW_FREQUENCY
BACK_LEFT
BACK_RIGHT
FRONT_LEFT_OF_CENTER
FRONT_RIGHT_OF_CENTER
BACK_CENTER
SIDE_LEFT
SIDE_RIGHT
TOP_CENTER
TOP_FRONT_LEFT
TOP_FRONT_CENTER
TOP_FRONT_RIGHT
TOP_BACK_LEFT
TOP_BACK_CENTER
TOP_BACK_RIGHT

One can define also special values for commomly used combinations, e.g.

STEREO (=FRONT_LEFT,FRONT_RIGHT) or 5POINT1
(=FRONT_LEFT,FRONT_RIGHT,FRONT_CENTER,LOW_FREQUENCY,BACK_LEFT,BACK_RIGHT).

Of course such a tag is only useful, if it is standardized or at least proposed
like the other tags in the docs.

If there is already a mechanism to map the channels to their spatial locations
please point me to the URL.

One additional question: The date tag should contain a date, I suppose. Do
values of this tag have a special format like the ISO date format, which is used
commonly in databases and is easily parsable, or is it just a text field, that
is not meant to be parsed by applications?

Regards Ingo

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At 01:25 PM 7/4/01 +0200, you wrote:
>Hallo,
>
>the specification in vorbis/doc proposes a set of comment tags, but I think
>there's one missing for multichannel configurations. There should be a
value for
>mapping the individual channels to spatial locations. Lets assume a Vorbis
>stream contains 4 channels, two front channels and two back channels, then
the
>corresponding comment value could be
Obviously, such a mapping will eventually be required. However, the comment
header is _only_ for human readable 'tags'. It is not, and will not be,
used
for important information like this, ever.
>If there is already a mechanism to map the channels to their spatial
locations
>please point me to the URL.
Not yet, but there will be. It'll be done properly.
>One additional question: The date tag should contain a date, I suppose. Do
>values of this tag have a special format like the ISO date format, which is
used
>commonly in databases and is easily parsable, or is it just a text field,
that
>is not meant to be parsed by applications?
We should probably recommend that the date tag be in a particular format, but
we won't require this (people would ignore such a requirement anyway, if we
did). Remember, it's not MEANT to be understood by applications, but having
a standard format here would be sensible.

Michael

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