rfc3190.txt

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   DV audio/video streams using the native DV block structure may use
   the payload format defined in [8] instead.

   Most of the existing RTP audio payload formats follow the AIFF-C
   convention for channel ordering as specified in [2] when sending more
   than two audio channels within a single RTP stream.  However, this
   convention does not cover some applications.  For example, some DV
   audio formats define a "woofer" channel, but AIFF-C does not include
   this frequency-dependent channel.  Thus, it is necessary to specify
   the audio channel allocation information explicitly when the contents
   of the audio stream are beyond the scope of AIFF-C.

   For DV audio streams of 4 or more channels, the channel order MUST be
   specified out-of-band.  This applies both to the payload formats
   defined in this document and to the L16 payload format.  A "channel-



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   order" parameter is defined here for this purpose and may be conveyed
   either as a MIME optional parameter or with the SDP a=fmtp attribute
   using the following syntax:

      a=fmtp:<payload type> channel-order=<convention>.<order>

   The first component of the value, <convention>, specifies the type of
   channel assignment convention used.  This allows for conventions
   other than AIFF-C and DV to be defined in the future.  This document
   defines only one convention for use in the channel-order parameter:

      DV

   The second component of the value, <order>, indicates the arrangement
   of channels within the stream.  The DV video specification [4]
   defines the types of audio channels that may be present and in what
   order.  The symbols used to denote the channel types are reproduced
   in the Appendix at the end of this document.  For the DV convention,
   the following values, which were formed from the concatenation of the
   individual channel symbols in the allowed channel orders, are defined
   for the <order> component:

      4 channels: LRLsRs, LRCS, LRCWo
      5 channels: LRLsRsC
      6 channels: LRLsRsCS, LmixRmixTWoQ1Q2
      8 channels: LRCWoLsRsLmixRmix, LRCWoLs1Rs1Ls2Rs2, LRCWoLsRsLcRc

   The <convention> and <order> symbols are case-insensitive, but are
   shown here in mixed case to make the individual channel symbols more
   apparent.  These concatenated symbols were deliberately constructed
   without separators to make clear the fact that the channels MUST NOT
   be assembled in other, arbitrary orders.

   For interworking with DV video systems, some of the audio encodings
   are defined only for a subset of the channel combinations listed
   above.  The DV video specification lists the channel combinations
   that are allowed for each encoding.

   The channel-order parameter MUST be consistent with the number of
   channels specified in the MIME optional parameter "channels" or in
   the a=rtpmap attribute of SDP.  For RTP audio streams of 1, 2 or 3
   channels, the AIFF-C channel order is used and is implicit in the
   number of audio channels specified.  To allow backward compatibility,
   the channel-order parameter MUST NOT be included in this case.

   Note that for the DV convention with 5 channels only one channel
   order is allowed, but for consistency the channel-order parameter
   MUST be included nonetheless.



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   An example of an SDP session description using the channel-order
   parameter is:

      v=0
      o=ikob 2890844526 2890842807 IN IP4 126.16.64.4
      s=POI (Audio only)
      i=A Seminar on making Presentations on the Internet
      u=http://www.koganei.wide.ad.jp/~ikob/POI/index.html
      e=[e-mail] (Katsushi Kobayashi)
      c=IN IP4 224.2.17.12/127
      t=2873397496 2873404696
      m=audio 49170 RTP/AVP 112 113
      a=rtpmap:112 L16/48000/2
      a=rtpmap:113 DAT12/32000/4
      a=fmtp:113 emphasis=50-15; channel-order=DV.LRCWO

   This session description shows the audio medium being transmitted in
   two formats, L16 and DAT12, using payload type numbers 112 and 113,
   respectively.  For the L16 format, the audio data contains 2-channel
   stereo following the implicit, default AIFF-C convention for left
   channel first and right channel second.  For the DAT12 format, the
   audio data contains 4 channels following the DV audio convention for
   the channels left, right, center, and woofer.

   This example also shows how multiple MIME optional parameters
   ("emphasis" and "channel-order") for these payload formats are mapped
   to a single a=fmtp attribute as a semicolon separated list of
   parameter=value pairs.

   The channel-order parameter described here provides a generic out-of-
   band mechanism to define alternatives to the AIFF-C channel order.
   However, if multi-channel audio data could be sent following the
   AIFF-C channel convention after simple processing, such as a data
   shuffling on the sender side, the alternative channel order SHOULD
   NOT be defined and instead the AIFF-C order SHOULD be employed to
   maximize interoperability.

   Moreover, multiple channels of audio data should only be multiplexed
   within a single RTP stream when all of the audio channels are
   intended to be reproduced together, such as the left and right
   channels in a stereo program.  Independent audio channels, such as
   multiple language translations, SHOULD be sent in separate RTP
   sessions.  This reduces bandwidth requirements by allowing receivers
   to tune in to only those channels which are desired.







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8. MIME registration

   This document defines some new RTP payload format names which are
   also registered as MIME subtypes: DAT12, L20 and L24.  The
   registration forms for these MIME subtypes are provided in the next
   sections.

8.1 MIME registration form for audio/DAT12

   MIME media type name: audio

   MIME subtype name: DAT12

   Required parameters:
      rate: number of samples per second -- RECOMMENDED values for rate
         are 8000, 11025, 16000, 22050, 24000, 32000, 44100 and 48000
         samples per second.  Other values are permissible.

   Optional parameters:
      channels: how many audio streams are interleaved -- defaults to 1;
         stereo would be 2, etc.  Interleaving takes place between
         individual 12-bit samples.

      emphasis: analog preemphasis applied to the data before
         quantization.  The only emphasis value defined here is
         emphasis=50-15 to indicate 50/15 microsecond preemphasis.  This
         parameter MUST be omitted if no analog preemphasis was applied.

      channel-order: specifies the sample interleaving order for
         multiple-channel audio streams (see RFC 3190 Section 7).
         Permissible values are DV.LRLsRs, DV.LRCS, DV.LRCWo,
         DV.LRLsRsC, DV.LRLsRsCS, DV.LmixRmixTWoQ1Q2,
         DV.LRCWoLsRsLmixRmix, DV.LRCWoLs1Rs1Ls2Rs2, DV.LRCWoLsRsLcRc.
         For interoperation with DV video systems, only a subset of
         these channel combinations is specified for use with 12-bit
         nonlinear encoding in the DV video specification [4]; that
         subset is all of the above except DV.LmixRmixTWoQ1Q2.  This
         parameter MUST be omitted when the AIFF-C channel order
         convention is in use.

   Encoding considerations:
      DAT12 audio can be transmitted with RTP as specified in RFC 3190.

   Security considerations: See Section 9.

   Interoperability considerations: NONE





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   Published specification:
      IEC 61119 Standard [4] and RFC 3190.

   Applications which use this media type:
      Audio communication.

   Additional information:
      Magic number(s): None
      File extension(s): None
      Macintosh File Type Code(s): None

   Person & email address to contact for further information:
      Katsushi Kobayashi
      e-mail: [e-mail]

   Intended usage: COMMON

   Author/Change controller:
      Katsushi Kobayashi
      e-mail: [e-mail]

8.2 MIME registration form for audio/L20

   MIME media type name: audio

   MIME subtype name: L20

   Required parameters:
      rate: number of samples per second -- RECOMMENDED values for rate
         are 8000, 11025, 16000, 22050, 24000, 32000, 44100 and 48000
         samples per second.  Other values are permissible.

   Optional parameters:
      channels: how many audio streams are interleaved -- defaults to 1;
         stereo would be 2, etc.  Interleaving takes place between
         individual 20-bit samples.

      emphasis: analog preemphasis applied to the data before
         quantization.  The only emphasis value defined here is
         emphasis=50-15 to indicate 50/15 microsecond preemphasis.  This
         parameter MUST be omitted if no analog preemphasis was applied.

      channel-order: specifies the sample interleaving order for
         multiple-channel audio streams (see RFC 3190 Section 7).
         Permissible values are DV.LRLsRs, DV.LRCS, DV.LRCWo,
         DV.LRLsRsC, DV.LRLsRsCS, DV.LmixRmixTWoQ1Q2,
         DV.LRCWoLsRsLmixRmix, DV.LRCWoLs1Rs1Ls2Rs2, DV.LRCWoLsRsLcRc.
         For interoperation with DV video systems, none of these channel



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         combinations is specified for use with 20-bit linear encoding
         in the DV video specification [4]; only mono and stereo are
         allowed.  This parameter MUST be omitted when the AIFF-C
         channel order convention is in use.

   Encoding considerations:
      L20 audio can be transmitted with RTP as specified in RFC 3190.

   Security considerations: See Section 9.

   Interoperability considerations: NONE

   Published specification:
      RFC 3190.

   Applications which use this media type:
      Audio communication.

   Additional information:
      Magic number(s): None
      File extension(s): None
      Macintosh File Type Code(s): None

   Person & email address to contact for further information:
      Katsushi Kobayashi
      e-mail: [e-mail]

   Intended usage: COMMON

   Author/Change controller:
      Katsushi Kobayashi
      e-mail: [e-mail]

8.3 MIME registration form for audio/L24

   MIME media type name: audio

   MIME subtype name: L24

   Required parameters:
      rate: number of samples per second -- RECOMMENDED values for rate
         are 8000, 11025, 16000, 22050, 24000, 32000, 44100 and 48000
         samples per second.  Other values are permissible.

   Optional parameters:
      channels: how many audio streams are interleaved -- defaults to 1;
         stereo would be 2, etc.  Interleaving takes place between
         individual 24-bit samples.



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      emphasis: analog preemphasis applied to the data before
         quantization.  The only emphasis value defined here is
         emphasis=50-15 to indicate 50/15 microsecond preemphasis.  This
         parameter MUST be omitted if no analog preemphasis was applied.

      channel-order: specifies the sample interleaving order for
         multiple-channel audio streams (see Section 7).  Permissible
         values are DV.LRLsRs, DV.LRCS, DV.LRCWo, DV.LRLsRsC,
         DV.LRLsRsCS, DV.LmixRmixTWoQ1Q2, DV.LRCWoLsRsLmixRmix,
         DV.LRCWoLs1Rs1Ls2Rs2, DV.LRCWoLsRsLcRc.  This parameter MUST be
         omitted when the AIFF-C channel order convention is in use.

   Encoding considerations:
      L24 audio can be transmitted with RTP as specified in RFC 3190.

   Security considerations: See Section 9.