[SIPForum-discussion] SDP attribute codec definitions

Mon Jun 23 07:13:32 UTC 2008

Hi,

Maybe you should check RFC 3555, later replaced by RFC 4855/4856 (what
you're looking for really is in 4856).

In theory, there should be all the fmtp parameters for the codecs defined in
the RTP profile for audio/video.

If the specific codec you're looking for is not one of them, then you can
probably find the proper information with its MIME type registration.

This can be found at the IANA, either "directly", or through the RFC of the
codec for RTP (check MIME registration part).

I personally use: http://www.iana.org/assignments/media-types/index.html

I can find what I need from there, even if it might not be the most
efficient way.

Regards,

Herve

  _____  

From: discussion-bounces at sipforum.org
[mailto:discussion-bounces at sipforum.org] On Behalf Of Malcolm Howlett
Sent: mercredi 18 juin 2008 16:40
To: sandeep01it22 at yahoo.co.in; discussion at sipforum.com
Subject: Re: [SIPForum-discussion] SDP attribute codec definitions

Thank you Sandeep, but whilst that might tell me what the base attributes
are, it doesn't tell me how to express them in an attribute line.

I suspect my initial email was poorly worded, so here's another go:-

If I take the following sample SDP

    m=video 5132 RTP/AVP 34 99\r\n

    a=rtpmap:34 h263-1998/90000\r\n

    a=fmtp:34 profile=0; level=10\r\n

    b=AS:48\r\n

    a=sendrecv\r\n

    a=rtcp:5133\r\n

    a=rtpmap:99 h264/90000\r\n

    a=fmtp:99 profile-level-id=420033; packetization-mode=0\r\n

    m=audio 5130 RTP/AVP 96 0 8 101\r\n

    a=rtpmap:96 amr/8000\r\n

    a=fmtp:96 mode-set=7; octet-align=1; robust-sorting=0\r\n

    a=sendrecv\r\n

    a=rtcp:5131\r\n

    a=maxptime:20\r\n

    a=ptime:20\r\n

    a=rtpmap:0 pcmu/8000\r\n

    a=silenceSupp:off - - -\r\n

    a=rtpmap:8 pcma/8000\r\n

    a=rtpmap:101 telephone-event/8000\r\n

    a=fmtp:101 0-15,36\r\n

I can estimate what some of the attributes mean, and I know which payload
type they refer to.

However, for example, to work out where to look to find what the line

    a=fmtp:34 profile=0; level=10\r\n

might mean for H263-1998, or even more importantly how to express other
attributes  in SDP that I might want to construct and send out.

In short is there any where that for each codec/payload type tells me what
attributes can be specified, and what text strings are used in order to
specify them in a universally understandable way?

Thanks

Malcolm

  _____  

From: Sandeep Mohapatra [mailto:sandeep01it22 at yahoo.co.in] 
Sent: 17 June 2008 18:36
To: discussion at sipforum.com; Malcolm Howlett
Subject: Re: [SIPForum-discussion] SDP attribute codec definitions

Hi Malcom,

You can refer to RFC-1890..
The snippet of the codec definitions from RFC-1890 is as follows.

PT         encoding      audio/video    clock rate    channels

                 name          (A/V)          (Hz)          (audio)

      _______________________________________________________________

      0          PCMU          A              8000          1

      1          1016          A              8000          1

      2          G721          A              8000          1

      3          GSM           A              8000          1

      4          unassigned    A              8000          1

      5          DVI4          A              8000          1

      6          DVI4          A              16000         1

      7          LPC           A              8000          1

      8         
 PCMA          A              8000          1

      9          G722          A              8000          1

      10         L16           A              44100         2

      11         L16           A              44100         1

      12         unassigned    A

      13         unassigned    A

      14         MPA           A              90000        (see text)

      15         G728          A              8000          1

      16--23     unassigned    A

      24         unassigned    V

      25         CelB          V              90000

      26         JPEG          V              90000

      27         unassigned    V

      28         nv            V              90000

      29         unassigned    V

      30         unassigned    V

      31         H261          V              90000

      32         MPV           V              90000

      33         MP2T          AV             90000

  34--71     unassigned    ?

      72--76     reserved      N/A            N/A           N/A

      77--95     unassigned    ?

      96--127    dynamic       ?

--- On Mon, 16/6/08, Malcolm Howlett <malcolm at c3.co.uk> wrote:

From: Malcolm Howlett <malcolm at c3.co.uk>
Subject: [SIPForum-discussion] SDP attribute codec definitions
To: discussion at sipforum.com
Date: Monday, 16 June, 2008, 9:33 PM

Dear folks

I understand the principle of media attributes in SDP as specified in RFCs
4566, 2327 etc. I am less clear as to where to find definitions of
attributes for each type of codec. Even for the most common of codecs such
as G711, I must admit I struggle to find a definitive list of attributes,
and what textual form they might take, and to interpret them all for the
setting of the RTP packetisers. 

Is there a repository of definitions anywhere, please?

Thanks

Malcolm Howlett

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