ref: 05bf400a7a7ae9cd2d9fa39b8d7b8e3b6edf5c92
parent: c763a35e9c1a5df1c983ee9f3588777e9560d12f
author: Ralph Giles <[email protected]>
date: Wed Dec 19 07:21:06 EST 2012
Update ogg draft based on comments from Tina le Grand. http://www.ietf.org/mail-archive/web/codec/current/msg02951.html
--- a/doc/draft-ietf-codec-oggopus.xml
+++ b/doc/draft-ietf-codec-oggopus.xml
@@ -423,7 +423,8 @@
<section anchor="headers" title="Header Packets">
<t>
-An Opus stream contains exactly two mandatory header packets.
+An Opus stream contains exactly two mandatory header packets:
+ an identification header and a comment header.
</t>
<section anchor="id_header" title="Identification Header">
@@ -506,8 +507,9 @@
This is the number of samples (at 48 kHz) to discard from the decoder
output when starting playback, and also the number to subtract from a page's
granule position to calculate its PCM sample position.
-When constructing cropped Ogg Opus streams, a pre-skip of at least
- 3,840 samples (80 ms) is RECOMMENDED to ensure complete convergence.
+When cropping the beginning of existing Ogg Opus streams, a pre-skip of at
+ least 3,840 samples (80 ms) is RECOMMENDED to ensure complete
+ convergence in the decoder.
<vspace blankLines="1"/>
</t>
<t><spanx style="strong">Input Sample Rate</spanx> (32 bits, unsigned, little
@@ -729,10 +731,32 @@
</t>
<t>Family 1 (Vorbis channel order):
<vspace blankLines="1"/>
-Allowed numbers of channels: 1...8.<vspace/>
-Channel meanings depend on the number of channels.
-See <xref target="vorbis-mapping"/> for the assignments from output channel
- number to specific speaker locations.
+Allowed numbers of channels: 1...8.
+<vspace/>
+Each channel is assigned to a speaker location in a conventional surround
+ configuration.
+Specific locations depend on the number of channels, and are given below
+ in order of the corresponding channel indicies.
+<list style="symbols">
+ <t>1 channel: monophonic (mono).</t>
+ <t>2 channels: stereo (left, right).</t>
+ <t>3 channels: linear surround (left, center, right)</t>
+ <t>4 channels: quadraphonic (front left, front right, rear left, rear right).</t>
+ <t>5 channels: 5.0 surround (front left, center, front right, rear left, rear right).</t>
+ <t>6 channels: 5.1 surround (front left, center, front right, rear left, rear right, LFE).</t>
+ <t>7 channels: 6.1 surround (front left, center, front right, side left, side right, rear center, LFE).</t>
+ <t>8 channels: 7.1 surround (front left, center, front right, side left, side right, rear left, rear right, LFE)</t>
+</list>
+This set of surround configurations and speaker location orderings is the same
+ as the one used by the Vorbis codec. <xref target="vorbis-mapping"/>
+The ordering is different from the one used by the
+ WAVE <xref target="wave-multichannel"/> and
+ FLAC <xref target="flac"/> formats,
+ although the configurations match, so correct ordering requires permutation
+ of the output channels when encoding from or decoding to those formats.
+Implementations SHOULD identify 'side' or 'rear' speaker locations with
+ 'surround' as appropriate when interfacing with audio formats or systems
+ which prefer that terminology.
<vspace blankLines="1"/>
</t>
<t>Family 255 (no defined channel meaning):
@@ -829,7 +853,7 @@
<vspace blankLines="1"/>
This is a simple human-readable tag for vendor information, encoded as a UTF-8
string <xref target="RFC3629"/>.
-No terminating NUL octet is required.
+No terminating null octet is required.
<vspace blankLines="1"/>
This tag is intended to identify the codec encoder and encapsulation
implementations, for tracing differences in technical behavior.
@@ -1094,6 +1118,15 @@
<!--?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.3550.xml"?-->
&rfc4732;
+<reference anchor="flac"
+ target="https://xiph.org/flac/format.html">
+ <front>
+ <title>FLAC - Free Lossless Audio Codec Format Description</title>
+ <author initials="J." surname="Coalson" fullname="Josh Coalson"/>
+ <date month="January" year="2008"/>
+ </front>
+</reference>
+
<reference anchor="replay-gain"
target="http://wiki.xiph.org/VorbisComment#Replay_Gain">
<front>
@@ -1124,6 +1157,15 @@
fullname="Christopher "Monty" Montgomery"/>
<date month="November" year="2008"/>
</front>
+</reference>
+
+<reference anchor="wave-multichannel"
+ target="http://msdn.microsoft.com/en-us/windows/hardware/gg463006.aspx">
+ <front>
+ <title>Multiple Channel Audio Data and WAVE Files</title>
+ <author fullname="Microsoft Corporation"/>
+ <date month="March" year="2007"/>
+ </front>
</reference>
</references>