Example SDP File

  • Updated on Sep 18, 2025
  • Published on Dec 17, 2024
  • 2 minute(s) read
  • Bryan Jones
  • Migration Team
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Scope

Sometimes you need an SDP file, but depending on what device you have, you might not be able to download one. That's OK, it's pretty easy to write your own. This article provides an example that you can follow.

If you are working with a Livewire device and you need to convert a Livewire channel to a multicast address, click here and use the calculator.

The example below presumes that the following are true. Change the values to suit your purpose:

  • The IP address of the device is 172.30.8.37 ('o' line)

  • Stream1 is the arbitrary name of the stream ('s' line)

  • The multicast address of the stream is 239.30.22.1 ('c' line)

  • The MAC address of the PTP clock generator is 01:23:45:67:89:AB:CD:EF('a=ts-refclk' line)

  • And the PTP domain is 127 (listed after the PTP mac address in the 'a=ts-refclk' line)

v=0
o=Node 1 1 IN IP4 172.30.8.37
s=Stream1
t=0 0
m=audio 5004 RTP/AVP 96
c=IN IP4 239.30.22.1
a=rtpmap:96 L24/48000/2
a=recvonly
a=ptime:1
a=ts-refclk:ptp=IEEE1588-2008:01-23-45-67-89-AB-CD-EF:127
a=mediaclk:direct=0
a=sync-time:0

Finally, save the text tile with the *.sdp extension.

The name of the file should match the stream name given in the 's' line for consistency, but is not required. In this example, Stream1.sdp

Breakdown of THIS example

There is no single place where you can find information about SDP files.  If you Google SDP files for AES67 or SMPTE-2110, you should find more than enough reading material.

v=0

Version: SDP protocol version. Always 0

o=Node 1 1 IN IP4 172.30.8.37

  • Origin field: Who/where the session was created

    • Node 1 → username or identifier of the session originator

    • 1 → session ID

    • 1 → session version.

    • IN → network type (Internet)

    • IP4 → address type (IPv4)

    • 172.30.8.37 → originating host's IP address

s=Stream1

  • Session name: A human-readable label for the stream ("Stream1")

t=0 0

  • Time: When the session is active.

    • 0 0 means "unbounded" — always active

m=audio 5004 RTP/AVP 96

  • Media description:

    • audio → media type

    • 5004 → port where RTP packets are sent

    • RTP/AVP → transport protocol (RTP using the Audio/Video Profile)

    • 96 → dynamic payload type number (to be defined in rtpmap)

c=IN IP4 239.30.22.1

  • Connection info:

    • IN → network type (Internet)

    • IP4 → IPv4

    • 239.30.22.1 → multicast address carrying the stream.

a=rtpmap:96 L24/48000/2

  • RTP mapping: Payload type 96 maps to L24 (linear PCM, 24-bit)

    • 48000 → sample rate (48 kHz)

    • 2 → channels (stereo).

a=recvonly

  • Direction attribute: This endpoint only receives media (no sending).

a=ptime:1

  • Packetization time: Each RTP packet contains 1 ms of audio.

a=ts-refclk:ptp=IEEE1588-2008:01-23-45-67-89-AB-CD-EF:127

  • Timestamp reference clock:

    • Uses IEEE 1588-2008 Precision Time Protocol (PTP)

    • 01-23-45-67-89-AB-CD-EF → the PTP grandmaster clock identity

    • 127 → domain number.

      • This tells receivers how RTP timestamps are tied to a reference clock.

a=mediaclk:direct=0

  • Media clock source:

    • direct=0 → the media clock is derived directly from the reference (in this case, the PTP clock).

---

a=sync-time:0

  • Synchronization time:

    • Indicates the media synchronization epoch

    • 0 → sync starts at RTP timestamp zero (reference point for alignment).

Put together: this SDP describes a multicast, 48 kHz, stereo, 24-bit LPCM audio stream sent via RTP to 239.30.22.1:5004, with packet timing and synchronization locked to an IEEE 1588 PTP clock.

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