ref: ccfad2756fba4076922f5c90993db2001cbc3b25
parent: f4695988cc920c7e867a2320ea32219059d4896e
author: Gregory Maxwell <[email protected]>
date: Wed Mar 4 08:31:49 EST 2009
A stereo example.
--- a/doc/ietf/draft-valin-celt-rtp-profile.xml
+++ b/doc/ietf/draft-valin-celt-rtp-profile.xml
@@ -490,7 +490,9 @@
Note that the RTP payload type code of 97 is defined in this media
definition to be 'mapped' to the CELT codec at a 48kHz sampling
frequency using the 'a=rtpmap' line. Any number from 96 to 127
-could have been chosen (the allowed range for dynamic types).
+could have been chosen (the allowed range for dynamic types). If there are
+is more than one channel being encoded the rtpmap MUST specify the channel
+count.
</t>
<t>
@@ -530,15 +532,8 @@
This examples illustrate an offerer that wishes to receive
a CELT stream at 44100 Hz, by packing two 512-sample frames in each packet.
</t>
-
-
-
-
</section>
-
-
-
<section anchor="Multichannel Mapping" title="Multichannel Mapping">
<t>
When more than two channels are used, a mapping parameter MUST be provided.
@@ -576,11 +571,12 @@
</t>
<t>
-Ambisonic channels MUST follow the "Malham notation" for up to third order spherical. Higher
-order ambisonic support is application defined but MUST NOT reuse any of WXYZRSTUVKLMNOPQ for
-higher order components. For example, second order spherical ambisonics SHOULD use the mapping
-"mapping=1,1,1,1,1,1,1,1,1/AW,AX,AY,AZ,AR,AS,AT,AU,AV". Any set of Ambisonic channels MUST
-contain at least one "AW" channel.
+Ambisonic channels MUST follow the Furse-Malham naming and weighing
+conventions for up to third order spherical<xref target="Higher-order-Ambisonic-systems"></xref>.
+Higher order ambisonic support is application defined but MUST NOT reuse any of WXYZRSTUVKLMNOPQ
+for higher order components. For example, second order spherical ambisonics SHOULD use the
+mapping "mapping=1,1,1,1,1,1,1,1,1/AW,AX,AY,AZ,AR,AS,AT,AU,AV". Any set of Ambisonic channels
+MUST contain at least one "AW" channel.
</t>
<t>
@@ -590,9 +586,23 @@
channels in 7.1 channel surround. Additional speaker-feeds are application specific but should not
reuse the prior identifiers.
For 5.1 surround in non-ambisonic form the mapping SHOULD be "mapping=2,2,1,1/L,R,LR,RR,C,MLFE/ITU-RBS.775-1".
-When only one or two channels are used, the mapping parameter MAY be omitted, in which case the default mapping is used. For one channel, the default is "mapping=1/C", while for two channels, the default is "mapping=2/L,R".
+When only one or two channels are used, the mapping parameter MAY be omitted, in which case the
+default mapping is used. For one channel, the default is "mapping=1/C", while for two channels,
+the default is "mapping=2/L,R".
</t>
+<t>
+For example a stereo configuration might signal:
+<vspace blankLines="1" />
+<list style="empty">
+<t>m=audio 8008 RTP/AVP 97</t>
+<t>a=rtpmap:97 CELT/44100/2</t>
+<t>a=fmtp:97 frame-size=256;nb-frames=1;</t>
+</list>
+Which specifies a single two-channel CELT stream according to the default
+mapping.
+</t>
+
</section>
@@ -606,10 +616,6 @@
</t>
<t>
-Do we support more than 2 channels (and how)?
-</t>
-
-<t>
Support for redundant data (how)?
</t>
@@ -806,6 +812,16 @@
<seriesInfo name="CELT website" value="http://www.celt-codec.org/" />
</reference>
+<reference anchor="Higher-order-Ambisonic-systems">
+<front>
+<title>Higher order Ambisonic systems</title>
+<author initials="D." surname="Malham" fullname="Dave
+Malham"><organization/></author>
+<date month="December" year="2003" />
+</front>
+<seriesInfo name="Paper"
+value="http://www.york.ac.uk/inst/mustech/3d_audio/higher_order_ambisonics.pdf" />
+</reference>
</references>