Sample SDP Specification
SDP (Session Description Protocol) for SMPTE requires the following fields to be present.
Fields must appear in the order shown below, except that multiple adjacent 'a' fields can be in any order.
The SDP format is defined by RFC4566 (https://tools.ietf.org/html/rfc4566). SMPTE SDP is defined in the ST2110-10-2017 standard.
Note: AES67 descriptors use the same format but do not support redundant flows.
Sample SDP for a Multicast Flow
v=0 o=- 123456 123458 IN IP4 10.0.1.2 s=My sample flow i=4 channels: c1, c2, c3, c4 t=0 0 a=recvonly m=audio 5004 RTP/AVP 98 c=IN IP4 239.69.11.44/32 a=rtpmap:98 L24/48000/4 a=ptime:1 a=ts-refclk:ptp=IEEE1588-2008:00-11-22-FF-FE-33-44-55:0 a=mediaclk:direct=0
Sample SDP for a Redundant Multicast Flow
v=0 o=- 345678 345979 IN IP4 10.0.1.2 s=My sample redundant flow i=2 channels: c6, c7 t=0 0 a=recvonly a=group:DUP prim sec m=audio 5004 RTP/AVP 98 c=IN IP4 239.69.22.33/32 a=rtpmap:98 L24/48000/2 a=ptime:1 a=ts-refclk:ptp=IEEE1588-2008:00-11-22-FF-FE-33-44-55:0 a=mediaclk:direct=0 a=mid:prim m=audio 5004 RTP/AVP 98 c=IN IP4 239.69.22.33/32 a=rtpmap:98 L24/48000/2 a=ptime:1 a=ts-refclk:ptp=IEEE1588-2008:00-11-22-FF-FE-33-44-55:0 a=mediaclk:direct=0 a=mid:prim m=audio 5004 RTP/AVP 98 c=IN IP4 239.69.44.55/32 a=rtpmap:98 L24/48000/2 a=ptime:1 a=ts-refclk:ptp=IEEE1588-2008:00-11-22-FF-FE-33-44-55:0 a=mediaclk:direct=0 a=mid:sec
Keys and Attributes
Session Level Keys
Key | Name | Example | Notes |
---|---|---|---|
v | Version | v=0 | Always zero |
o | Origin | o=- 345678 345979 IN IP4 10.0.1.2 | See https://tools.ietf.org/html/rfc4566#section-5.2 for details |
s | Session name | s=My sample redundant flow | Non-empty text string 'naming' flow |
i | Session information | i=2 channels: c6, c7 |
|
c | Connection information | c=IN IP4 239.69.22.33/32 |
|
t | Time description | t=0 0 |
|
Session Level Attributes
Attribute | Example | Notes |
---|---|---|
Receive-only session | a=recvonly | Multicast flows are receive only |
Media grouping | a=group:DUP prim sec |
|
Media Level Keys
Key | Name | Example | Notes |
---|---|---|---|
m | Media name and transport | m=audio 5004 RTP/AVP 98 |
|
c | Connection data | c=IN IP4 239.69.22.33/32 |
|
Media Level Attributes
Attribute | Example | Notes |
---|---|---|
RTP payload type mapping | a=rtpmap:98 L24/48000/2 |
|
RTP packet time | a=ptime:1 |
|
Reference clock | a=ts-refclk:ptp=IEEE1588-2008:00-11-22-FF-FE-33-44-55:0 |
|
Clock mapping | a=mediaclk:direct=0 |
|
Media identifier | a=mid:prim |
|
Other fields and attributes are ignored by Dante devices.
If there is no a=group:DUP attribute then the first valid audio media descriptor is used and any further descriptors are ignored. If there is an a=group:DUP attribute then only the specified media descriptors are used, and any others are ignored.
Note: Descriptors that are legal SDP but not well-formed for SMPTE will be silently ignored by Dante Controller and Dante devices.