minor Vorbis specification amendment proposal

Hi

Vorbis has 3 "global" header packets, while
generic containers generally
have only a single global header per stream

my proposal to solve this, would be to add a few lines to
the vorbis
specification to clarify how to convert between the 3
headers and the single
header needed for non ogg containers
currently (without any standarized way) various groups
simply use their own
self-invented method to store vorbis in non ogg and
consequently either
merge the 3 headers as they see fit or just dump them into
the file like
normal packets leading to problems with random access
(seeking) ... 
all that leads to many problems and incompatibilites


Proposed amendment------------

To split a global header from a non ogg container:

1) search for the 1st occurance of
01,'v','o','r','b','i','s'
   the found match and the following 23 bytes are the 1st
header packet
2) search for the 1st occurance of
03,'v','o','r','b','i','s' after here
  3) read an unsigned integer of 32 bits and skip that many
bytes
  4) [user_comment_list_length] = read an unsigned integer
of 32 bits
  5) iterate [user_comment_list_length] times {
       6) read an unsigned integer of 32 bits and skip that
many bytes
     }
  7) skip 1 byte
8) the match in 2) and what follows until here is the 2nd
header packet
9) search for the 1st occurance of
05,'v','o','r','b','i','s' after here
   the matching part and what follows is the 3rd header
packet

To convert the 3 header packets to a single one for storege
in a non ogg
container, simple concatenate the 3 header packets without
anything before,
after or between them

-------------------------------

the proposed spliting method will work with pretty much any
way the
packets can be merged, it will specifically work with
1. simple concatenation
2. the format in matroska (2<p1 size><p2
size><p1><p2><p3>, sizes stored 
   like packet sizes in ogg)
3. 16/32bit size for packet 0, packet 0, 16/32bit size for
packet 1, ...
4. 16bit size for packet 0, 16bit size for packet 1, ...,
packet 0, ...
5. 16/32bit size for packet 0, 16/32bit size for packet 1,
packet 0, ...

one format it could fail with is if the 3 32bit sizes are
put infront of 
the 3 packets, though that would require the packets to be
large 
(giga bytes) for it to fail

-- 
Michael     GnuPG fingerprint:
9FF2128B147EF6730BADF133611EC787040B0FAB

In the past you could go to a library and read, borrow or
copy any book
Today you'd get arrested for mere telling someone where the
library is
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Hi

Vorbis has 3 "global" header packets, while
generic containers generally
have only a single global header per stream

my proposal to solve this, would be to add a few lines to
the vorbis
specification to clarify how to convert between the 3
headers and the single
header needed for non ogg containers
currently (without any standarized way) various groups
simply use their own
self-invented method to store vorbis in non ogg and
consequently either
merge the 3 headers as they see fit or just dump them into
the file like
normal packets leading to problems with random access
(seeking) ... 
all that leads to many problems and incompatibilites


Proposed amendment------------

To split a global header from a non ogg container:

1) search for the 1st occurance of
01,'v','o','r','b','i','s'
   the found match and the following 23 bytes are the 1st
header packet
2) search for the 1st occurance of
03,'v','o','r','b','i','s' after here
  3) read an unsigned integer of 32 bits and skip that many
bytes
  4) [user_comment_list_length] = read an unsigned integer
of 32 bits
  5) iterate [user_comment_list_length] times {
       6) read an unsigned integer of 32 bits and skip that
many bytes
     }
  7) skip 1 byte
8) the match in 2) and what follows until here is the 2nd
header packet
9) search for the 1st occurance of
05,'v','o','r','b','i','s' after here
   the matching part and what follows is the 3rd header
packet

To convert the 3 header packets to a single one for storege
in a non ogg
container, simple concatenate the 3 header packets without
anything before,
after or between them

-------------------------------

the proposed spliting method will work with pretty much any
way the
packets can be merged, it will specifically work with
1. simple concatenation
2. the format in matroska (2<p1 size><p2
size><p1><p2><p3>, sizes stored 
   like packet sizes in ogg)
3. 16/32bit size for packet 0, packet 0, 16/32bit size for
packet 1, ...
4. 16bit size for packet 0, 16bit size for packet 1, ...,
packet 0, ...
5. 16/32bit size for packet 0, 16/32bit size for packet 1,
packet 0, ...

one format it could fail with is if the 3 32bit sizes are
put infront of 
the 3 packets, though that would require the packets to be
large 
(giga bytes) for it to fail

-- 
Michael     GnuPG fingerprint:
9FF2128B147EF6730BADF133611EC787040B0FAB

In the past you could go to a library and read, borrow or
copy any book
Today you'd get arrested for mere telling someone where the
library is
_______________________________________________
NUT-devel mailing list
NUT-develmplayerhq.hu

http://lists.mplayerhq.hu/mailman/listinfo/nut-devel

On Thu, Jul 20, 2006 at 03:56:48PM +0200, Michael
Niedermayer wrote:

> Vorbis has 3 "global" header packets, while
generic containers generally
> have only a single global header per stream

I think this is a useful idea, but giving specific parse
rules to try on 
*any* container format seems unwise. I'd rather see an
appendix 
documenting a standard embedding proceedure for various
other 
containers, and perhaps some guidelines for creating new
mappings 
including the parsability information you included.

Would you be willing to write up and contribute something
like that?

 -r
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