[Live-devel] Doubts reagrding the SDP informations sent for MP3

[Ross Finlayson]

>
>May I know why the LiveMediaServer is not sending rtpmap information?
>
>With the Helix server, I tried streaming a Mp3 clip using VLC player.
>
>The SDP Information sent by the Helix Server is as follows,
>
>a=rtpmap:101 X-MP3-draft-00/44100/2
>
>In our Application, If this information is coming through SDP then 
>major overhead can be avoided.
>
>This information comes even for 3gp clips why not for mp3??
>
>Kindly through some light on this.

The "a=rtpmap:" line is needed only for dynamic payload type numbers 
(e.g., 101 in this case), for which a RTP payload format is not 
already defined.  For MPEG-1 or 2 audio (including 'mp3'), however, a 
static payload type of 14 is already defined for this RTP payload 
format (see Table 4 in RFC 3551), and we use that instead (note the 
line "m=audio 0 RTP/AVP 14").  Because of this, a "a=rtpmap:" line is 
not needed.

Note that receivers that use our code do not need to concern 
themselves with this, because we handle the SDP description 
automatically.

(Note also that the "X-MP3-draft-00" in the Helix server's SDP line 
tells us that it using an experimental RTP payload format; not an 
IETF standard one.  Standard receivers therefore cannot be expected 
to receive that stream.)
-- 

Ross Finlayson
Live Networks, Inc.
http://www.live555.com/