Vorbis - Jun 2001 - file(1) magic for Ogg Vorbis

I downloaded `file' for djgpp, and it verbosly identified my mp3 by
bitrate, sample rate, mono/stereo, option bits, etc.  WAVs are also
uidentified well.  Only vorbis was identified simply as "Ogg-Vorbis
compressed sound file" without any info.  So I decided I must fix this to
replace my aliases that use `od' to read the bitrate and number of
channels.

Here is the result (attached).  I need your feedback before sending to the
maintainer <christos@astron.com>:

- Magic:
  + I currently check for Ogg framing of the first page and vorbis headers
on first and second packets (which are also separate pages).  Should I
check less/more?
    * Partial recognition is possible, i.e. Ogg but not vorbis, or first
vorbis header but no comment header.  What should be printed then?  I
should probably fix it to print "Ogg data" not just "Ogg" in
case it's not
vorbis.
  + I verify the ogg reverion and the encoder version to be 0.  Should I?
Is the encoder version checked at the right place at all (first thing
after `\x01vorbis', before the number of channels)?

- I report way too much for the average user.  What would you like too
see?  I guess the following should be commented out (but left there for
somebody needing it to turn on):
  + The "revision 0" and "version 0" messages (the normal
case).
  + Serial number - does anybody care?
  + The heavy vendor string, probably only the beta number should be
printed (exact cvs date?).
  + The "no comments" message (but leave the "%lu comments"
for >0).

- Are the beta dates correct?  What was beta1's date?  Any other releases
you wish to identify?  (I will maintain the entry to track future
releases.)

- Is anything else possible to detect (for the fun of it)?


-- 
Beni Cherniavsky <cben@crosswinds.net>
                 (also scben@t2,cben@tx in Technion)

PS: The magic(4) format has probably been designed for viewing in email
readers that highlight quotations ;-)



<HR NOSHADE>
<UL>
<LI>TEXT/PLAIN attachment: magic.txt
</UL>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: magic.txt
Type: application/octet-stream
Size: 2077 bytes
Desc: not available
Url :
http://lists.xiph.org/pipermail/vorbis/attachments/20010617/bc1f3539/magic-0001.obj

On Sun, Jun 17, 2001 at 12:40:53PM +0300, Beni Cherniavsky
wrote:
> I downloaded `file' for djgpp, and it verbosly identified my mp3 by
> bitrate, sample rate, mono/stereo, option bits, etc.  WAVs are also
> uidentified well.  Only vorbis was identified simply as "Ogg-Vorbis
> compressed sound file" without any info.  So I decided I must fix this
to
> replace my aliases that use `od' to read the bitrate and number of
> channels.
> 
> Here is the result (attached).  I need your feedback before sending to the
> maintainer <christos@astron.com>:
> 
> - Magic:
>   + I currently check for Ogg framing of the first page and vorbis headers
> on first and second packets (which are also separate pages).  Should I
> check less/more?
It is sufficient to check the first page/packet.  Second is overkill,
but if you're getting the comments, I guess it can't hurt.
>     * Partial recognition is possible, i.e. Ogg but not vorbis, or first
> vorbis header but no comment header.  What should be printed then?  I
> should probably fix it to print "Ogg data" not just
"Ogg" in case it's not
> vorbis.
No official in-stone spec for other codecs yet.  Vorbis I, however,
will always follow the current magic.
>   + I verify the ogg reverion and the encoder version to be 0.  Should I?
Yes, a good idea.
> Is the encoder version checked at the right place at all (first thing
> after `\x01vorbis', before the number of channels)?
Correct.  32 bits, LSB first immediately after \0x01vorbis.
> - I report way too much for the average user.  What would you like too
> see?  I guess the following should be commented out (but left there for
> somebody needing it to turn on):
>   + The "revision 0" and "version 0" messages (the
normal case).
Sure.
>   + Serial number - does anybody care?
Very unlikely.  Advanced usageonly would be my preference. 
>   + The heavy vendor string, probably only the beta number should be
> printed (exact cvs date?).
I'd say make this advanced usage too, really...  This string does not
actually require a specific format and parsing out date will
eventually break.
>   + The "no comments" message (but leave the "%lu
comments" for >0).
comments are up to you. :-)
> - Are the beta dates correct?  What was beta1's date?  Any other
releases
> you wish to identify?  (I will maintain the entry to track future
> releases.)
20000508 IIRC.  There are more dates floating around from intermediate
CVS versions.
> - Is anything else possible to detect (for the fun of it)?
ample rate, # channels would be the only other thing I'd always print.

Monty

--- >8 ----
List archives:  http://www.xiph.org/archives/
Ogg project homepage: http://www.xiph.org/ogg/
To unsubscribe from this list, send a message to
'vorbis-request@xiph.org'
containing only the word 'unsubscribe' in the body.  No subject is
needed.
Unsubscribe messages sent to the list will be ignored/filtered.