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misc changes to rtp draft

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This commit is contained in:
Jean-Marc Valin 2009-02-27 17:12:09 -05:00
parent aa4c217f2a
commit af2b0f7e69
1 changed files with 13 additions and 15 deletions
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28
doc/ietf/draft-valin-celt-rtp-profile.xml
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@ -38,7 +38,7 @@
</address> </address>
</author> </author>
<date day="20" month="November" year="2008" /> <date day="27" month="February" year="2009" />
<area>General</area> <area>General</area>
<workgroup>AVT Working Group</workgroup> <workgroup>AVT Working Group</workgroup>
@ -50,11 +50,12 @@
<abstract> <abstract>
<t> <t>
CELT is an open-source voice codec suitable for use in very low delay CELT is an open-source voice codec suitable for use in very low delay
Voice over IP (VoIP) type applications. This document describes the payload audio communication applications, including Voice over IP (VoIP).
format for CELT generated bit streams within an RTP packet. Also This document describes the payload format for CELT generated bit
included here are the necessary details for the use of CELT with streams within an RTP packet. Also included here are the necessary
the Session Description Protocol (SDP). At the time of this writing, the CELT details for the use of CELT with the Session Description Protocol
bit-stream has NOT been finalized yet, and compatibility is usually broken with (SDP). At the time of this writing, the CELT bit-stream has NOT
been finalized yet, and compatibility is usually broken with
every new release of the codec. every new release of the codec.
</t> </t>
</abstract> </abstract>
@ -78,7 +79,7 @@ CELT stands for "Constrained Energy Lapped Transform". It applies some of the CE
<t> <t>
<list style="symbols"> <list style="symbols">
<t>Ultra-low latency (typically from 3 to 9 ms)</t> <t>Ultra-low algorithmic delay (typically from 3 to 9 ms)</t>
<t>Full audio bandwidth (44.1 kHz and 48 kHz)</t> <t>Full audio bandwidth (44.1 kHz and 48 kHz)</t>
<t>Support for both voice and music</t> <t>Support for both voice and music</t>
<t>Stereo support</t> <t>Stereo support</t>
@ -189,12 +190,9 @@ CELT the following values are used.
<t>Timestamp: 32 bits</t><t> <t>Timestamp: 32 bits</t><t>
A timestamp representing the sampling time of the first sample of A timestamp representing the sampling time of the first sample of
the first CELT frame in the RTP packet. The clock frequency the first CELT frame in the RTP payload. The clock frequency
MUST be set to the sample rate of the encoded audio data. MUST be set to the sample rate of the encoded audio data and is
conveyed out-of-band (e.g., as an SDP parameter).
CELT can use different frame sizes and a variable sampling rate clock.
The RTP timestamp MUST be in units of 1/X of a second where X
is the sample rate used.
</t> </t>
<t>SSRC/CSRC identifiers:</t><t> <t>SSRC/CSRC identifiers:</t><t>
@ -292,9 +290,9 @@ The bit-rate used by CELT is implicitly determined by the size of the
compressed data. When more than one frame is encoded in the same packet, compressed data. When more than one frame is encoded in the same packet,
it is not possible to determine the size of each encoded frame, so the it is not possible to determine the size of each encoded frame, so the
information must be explicitly encoded. If N frames are present in a information must be explicitly encoded. If N frames are present in a
packet, N-1 values compressed frame sizes need to be encoded at the packet, N-1 compressed frame sizes need to be encoded at the
beginning of the packet. Each size that is less than 255 bytes is encoded beginning of the packet. Each size that is less than 255 bytes is encoded
in one byte. For sizes greater or equal to 255, a 0xff byte is encoded, in one byte (unsigned 8-bit integer). For sizes greater or equal to 255, a 0xff byte is encoded,
followed by the size-255. Multiple 0xff bytes are allowed if there are followed by the size-255. Multiple 0xff bytes are allowed if there are
more than 510 bytes transmitted. A size of zero indicates silence for the more than 510 bytes transmitted. A size of zero indicates silence for the
current frame. current frame.