Difference between revisions of "Oggless"

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{{draft}}
 
 
 
==Abstract==
 
==Abstract==
This page will document how to embed the different Xiph codecs like Vorbis or Theora in containers other than Ogg.  It's still in the drating stage, and most of it was taken from the [http://svn.mplayerhq.hu/nut/docs/oggless-xiph-codecs.txt?view=log MPlayer SVN], authored by Michael Niedermayer.
+
This page documents how to embed the different Xiph codecs like Vorbis or Theora in containers other than Ogg.  It's still in the drafting stage, and most of it was taken from a [http://svn.mplayerhq.hu/nut/docs/oggless-xiph-codecs.txt?revision=486&pathrev=577 version] that was previously a part of the NUT Subversion repository.
 +
Said document was originally authored by Michael Niedermayer.
  
 
==Current Version==
 
==Current Version==
* 2007-07-07
+
* 2007-07-21
  
 
==Status==
 
==Status==
This is a proposal being discussedIt's currently not ready to be used on real-life situations.
+
Information on how to convert losslessly from one format to another is missing, as is Ogg timestampingRegardless, it is mostly finished and likely won't be updated further.
  
 
==Minimum container requirements==
 
==Minimum container requirements==
This appendix only explains how to store xiph codecs in containers which  
+
This appendix only explains how to store Xiph codecs in containers which  
support at least one global header per stream, can separate individual codec
+
support at least one global header per stream, can separate individual codec packets and in principle support the codec. So for example in the case of Vorbis, that would be variable bitrate and variable number of samples/packetStorage in other containers is outside the scope of this appendix.
packets and in principle support the codec, so for example in the case of
 
vorbis that would be variable bitrate and variable number of samples/packet
 
Storage in other containers is outside the scope of this appendix
 
  
 +
===Global header:===
 +
If the container can store 3 headers per stream in an unambiguous and ordered way then they shall be stored in that way. If OTOH the container is only capable of storing a single global header, then the 3 codec headers shall be concatenated without any additional header, footer or separator between them. To recover the 3 headers from such a global header the following procedure shall be used:
  
FIXME non vorbis/theora
+
: 1) Search for the 1st occurrence of ID1. The found match and the following ID1_LEN bytes are the 1st header packet.
===Global header:===
 
If the container can store 3 headers per stream in an unambiguous and ordered
 
way then they shall be stored in that way, if OTOH the container is only
 
capable to store a single global header then the 3 codec headers shall be
 
concatenated without any additional header, footer or separator between them
 
to recover the 3 headers from such a global header the following procedure
 
shall be used:
 
: 1) search for the 1st occurrence of ID1 the found match and the following ID1_LEN bytes are the 1st header packet
 
 
: 2) search for the 1st occurrence of ID2 after here
 
: 2) search for the 1st occurrence of ID2 after here
 
:: 3) read an unsigned integer of 32 bits and skip that many bytes
 
:: 3) read an unsigned integer of 32 bits and skip that many bytes
Line 35: Line 25:
 
:: 7) skip 1 byte
 
:: 7) skip 1 byte
 
: 8) the match in 2) and what follows until here is the 2nd header packet
 
: 8) the match in 2) and what follows until here is the 2nd header packet
: 9) search for the 1st occurrence of ID3 after here the matching part and what follows is the 3rd header packet
+
: 9) Search for the 1st occurrence of ID3 after here. The matching part and what follows is the 3rd header packet.
  
 
====Constants:====
 
====Constants:====
{|
+
{| border="1" cellpadding="4"
 
! Codec
 
! Codec
 
! ID1
 
! ID1
Line 58: Line 48:
 
|}
 
|}
  
if the container needs an identifier for the global header, for example a 4cc
+
If the container needs an identifier for the global header, for example a fourcc for a global header chunk then glbl shall be used.
for a global header chunk then glbl shall be used
 
  
  
 
===Storing packets:===
 
===Storing packets:===
Each codec packet shall be stored in exactly one "container packet"
+
Each codec packet shall be stored in exactly one "container packet" and one "container packet" must not contain more then one codec packet. "container packet" here means the smallest separable data unit in the container.
and one "container packet" must not contain more then one codec packet
 
"container packet" here means the smallest separatable unit of data in the
 
container
 
  
  
 
===Codec Identifier:===
 
===Codec Identifier:===
{|
+
{| border="1" cellpadding="4"
! xiph-codec
+
! Xiph codec
! 4-cc id
+
! fourcc ID
! long id
+
! long ID
 
|-
 
|-
 
| Vorbis       
 
| Vorbis       
Line 87: Line 73:
 
| tarkin
 
| tarkin
 
|-
 
|-
| Flac
+
| FLAC
 
| flac
 
| flac
 
| flac
 
| flac
Line 97: Line 83:
 
|}
 
|}
  
if the container uses 4-character codes 4-cc identifier from the table above
+
If the container uses 4-character codes, the fourcc identifier from the table above shall be used. If the container uses arbitrary length strings as identifiers, then the long ID from the table above shall be used.
shall be used
 
if the container uses arbitrary length strings as identifiers then the long
 
id from the table above shall be used
 
  
 +
===Examples and Discussions about specific containers===
 +
What follows are some notes about specific containers, these notes are just informative as they just repeat what is written above or in the
 +
specification of the specific container.
  
===Examples and Discussions about specific containers===
+
====Example and Discussion of the AVI container====
What follows are some notes about specific containers, these notes are just
+
AVI supports everything needed to store Vorbis, this does not mean that all applications will support Vorbis in AVI, as Vorbis is rather different from other audio codecs commonly stored in AVI.
informative as they just repeat what is written above or in the
 
specification of the specific container
 
  
 +
AVI supports a single global header like WAV does, the 3 Vorbis headers
 +
shall be stored in it and only in it as described above.  dwSampleSize must be set to zero as vorbis is VBR, many applications do this incorrectly for other VBR codecs and consequently VBR audio in AVI
 +
becomes problematic.
  
====Example and Discussion of the avi container====
+
AVI does not have timestamps, but each chunk has a constant duration,
avi supports everything needed to store vorbis, this does not mean that all
+
while Vorbis packets can have one of 2 durations.
application will support vorbis in avi as vorbis is rather different from
+
If now the AVI header is set up in a way that each AVI chunk has the
other audio codecs commonly stored in avi ...
+
same duration as the smaller duration of the 2 possibilities in Vorbis,
avi supports a single global header like wav does, the 3 vorbis headers
+
then simply inserting empty AVI chunks will allow every AVI chunk to
shall be stored in it and only in it as described above
+
have the correct duration.
dwSampleSize must be set to zero as vorbis is vbr, many applications do
+
This is of course not the most beautiful solution but it is the only way
this incorrectly for other vbr codecs and consequently vbr audio in avi
+
to keep things exact.
becomes problematic
+
Additionally, note that empty chunks have been used since ages in AVI to
avi does not have timestamps but each chunk has a constant duration, while
+
lengthen the duration of video chunks.
vorbis packets can have one of 2 durations, if now the avi header is setup
 
so that each avi chunk has the same duration as the smaller duration of
 
the 2 possibilities in vorbis then simply inserting empty avi chunks will
 
allow every avi chunk to have the correct duration, this is of course
 
not the most beautiful solution but it is the only way to keep things
 
exact, additionally note, that empty chunks have been used since ages
 
in avi to lengthen the duration of video chunks
 
  
 
Some Links:
 
Some Links:
* [http://svn.xiph.org/tags/vorbisacm_20020708/ vorbisacm]
+
* [http://svn.xiph.org/tags/vorbisacm_20020708/ Vorbisacm]
 
* [http://www.alexander-noe.com/video/documentation/avi.pdf AVI File Format] (PDF), 5.7 (p.21) VFR Audio - Storing Vorbis in AVI
 
* [http://www.alexander-noe.com/video/documentation/avi.pdf AVI File Format] (PDF), 5.7 (p.21) VFR Audio - Storing Vorbis in AVI
  
====Example and Discussion of the asf container====
+
====Example and Discussion of the ASF container====
asf supports a single global header per stream and has timestamps so
+
ASF supports a single global header per stream and has timestamps, so
storing xiph codecs in it should be possible but asf is patented and  
+
storing Xiph codecs in it should be possible, but ASF is patented and  
microsoft has already threatened individuals so we strongly urge you to  
+
Microsoft has already threatened individuals, so we strongly urge you to  
avoid this container
+
avoid this container.
 
 
 
 
====Example and Discussion of the matroska container====
 
matroska supports storing 3 headers using a codec specific
 
format, which should be used for storing the 3 headers
 
Note, the above procedure to split one header into 3 works with the
 
vorbis-matroska specific format too
 
 
 
  
====Example and Discussion of the nut container====
+
====Example and Discussion of the Matroska container====
nut supports a single global header per stream so the 1<->3 merge/split
+
Matroska supports storing 3 headers using a codec-specific format.
procedure above must be used, except that theres nothing special with
+
This should be used for storing the 3 headers.
storing xiph codecs in nut
 
  
 +
Note that the above procedure to split one header into 3 works with the
 +
Vorbis-Matroska-specific format, too.
  
====Example and Discussion of mpeg-ps / mpeg-ts container====
+
====Example and Discussion of the NUT container====
These containers neither support a global header nor provide the neccessary
+
NUT supports a single global header per stream so the 1<->3 merge/split
packet separation / framing, so storing xiph codecs in them is outside the
+
procedure above must be used. Except that there is nothing special with
scope of this appendix
+
storing Xiph codecs in NUT.
  
 +
====Example and Discussion of MPEG-PS / MPEG-TS container====
 +
These containers neither support a global header nor do they provide
 +
the necessary packet separation / framing.
 +
Storing Xiph codecs in them is thus outside the scope of this appendix.
  
====Example and Discussion of wav container====
+
====Example and Discussion of WAV container====
wav does not provide the necessary packet separation / framing, so storing  
+
WAV does not provide the necessary packet separation / framing, so storing Xiph codecs in it is outside the scope of this appendix.
xiph codecs in it is outside the scope of this appendix
 
  
 +
====Example and Discussion of the MOV container====
 +
A single glbl atom shall be placed in the stsd atom in which the the global header shall be stored.
  
====Example and Discussion of the mov container====
+
[[Category:Drafts]]
a single glbl atom shall be placed in the stsd atom in which the the global
 
header shall be stored
 

Revision as of 15:27, 15 February 2008

Abstract

This page documents how to embed the different Xiph codecs like Vorbis or Theora in containers other than Ogg. It's still in the drafting stage, and most of it was taken from a version that was previously a part of the NUT Subversion repository. Said document was originally authored by Michael Niedermayer.

Current Version

  • 2007-07-21

Status

Information on how to convert losslessly from one format to another is missing, as is Ogg timestamping. Regardless, it is mostly finished and likely won't be updated further.

Minimum container requirements

This appendix only explains how to store Xiph codecs in containers which support at least one global header per stream, can separate individual codec packets and in principle support the codec. So for example in the case of Vorbis, that would be variable bitrate and variable number of samples/packet. Storage in other containers is outside the scope of this appendix.

Global header:

If the container can store 3 headers per stream in an unambiguous and ordered way then they shall be stored in that way. If OTOH the container is only capable of storing a single global header, then the 3 codec headers shall be concatenated without any additional header, footer or separator between them. To recover the 3 headers from such a global header the following procedure shall be used:

1) Search for the 1st occurrence of ID1. The found match and the following ID1_LEN bytes are the 1st header packet.
2) search for the 1st occurrence of ID2 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 occurrence of ID3 after here. The matching part and what follows is the 3rd header packet.

Constants:

Codec ID1 ID2 ID3 ID1_LEN
Vorbis 0x01,'v','o','r','b','i','s' 0x03,'v','o','r','b','i','s' 0x05,'v','o','r','b','i','s' 23
Theora 0x80,'t','h','e','o','r','a' 0x81,'t','h','e','o','r','a' 0x82,'t','h','e','o','r','a' 35

If the container needs an identifier for the global header, for example a fourcc for a global header chunk then glbl shall be used.


Storing packets:

Each codec packet shall be stored in exactly one "container packet" and one "container packet" must not contain more then one codec packet. "container packet" here means the smallest separable data unit in the container.


Codec Identifier:

Xiph codec fourcc ID long ID
Vorbis vrbs vorbis
Theora ther theora
Tarkin trkn tarkin
FLAC flac flac
Speex spex speex

If the container uses 4-character codes, the fourcc identifier from the table above shall be used. If the container uses arbitrary length strings as identifiers, then the long ID from the table above shall be used.

Examples and Discussions about specific containers

What follows are some notes about specific containers, these notes are just informative as they just repeat what is written above or in the specification of the specific container.

Example and Discussion of the AVI container

AVI supports everything needed to store Vorbis, this does not mean that all applications will support Vorbis in AVI, as Vorbis is rather different from other audio codecs commonly stored in AVI.

AVI supports a single global header like WAV does, the 3 Vorbis headers shall be stored in it and only in it as described above. dwSampleSize must be set to zero as vorbis is VBR, many applications do this incorrectly for other VBR codecs and consequently VBR audio in AVI becomes problematic.

AVI does not have timestamps, but each chunk has a constant duration, while Vorbis packets can have one of 2 durations. If now the AVI header is set up in a way that each AVI chunk has the same duration as the smaller duration of the 2 possibilities in Vorbis, then simply inserting empty AVI chunks will allow every AVI chunk to have the correct duration. This is of course not the most beautiful solution but it is the only way to keep things exact. Additionally, note that empty chunks have been used since ages in AVI to lengthen the duration of video chunks.

Some Links:

Example and Discussion of the ASF container

ASF supports a single global header per stream and has timestamps, so storing Xiph codecs in it should be possible, but ASF is patented and Microsoft has already threatened individuals, so we strongly urge you to avoid this container.

Example and Discussion of the Matroska container

Matroska supports storing 3 headers using a codec-specific format. This should be used for storing the 3 headers.

Note that the above procedure to split one header into 3 works with the Vorbis-Matroska-specific format, too.

Example and Discussion of the NUT container

NUT supports a single global header per stream so the 1<->3 merge/split procedure above must be used. Except that there is nothing special with storing Xiph codecs in NUT.

Example and Discussion of MPEG-PS / MPEG-TS container

These containers neither support a global header nor do they provide the necessary packet separation / framing. Storing Xiph codecs in them is thus outside the scope of this appendix.

Example and Discussion of WAV container

WAV does not provide the necessary packet separation / framing, so storing Xiph codecs in it is outside the scope of this appendix.

Example and Discussion of the MOV container

A single glbl atom shall be placed in the stsd atom in which the the global header shall be stored.