# Format of an SDP file for audio


```
v=0
o=- 1443716955 1443716955 IN IP4 10.xx.xxx.236
s=st2110 0-1-0
t=0 0
m=audio 20000 RTP/AVP 97
c=IN IP4 239.x.x.x/64
a=source-filter: incl IN IP4 239.x.x.x 10.xx.xxx.236
a=rtpmap:97 L24/48000/2
a=mediaclk:direct=0 rate=48000
a=framecount:48
a=ptime:1
a=ts-refclk:ptp=IEEE1588-2008:04-5c-6c-ff-fe-0a-53-70:127
```

Following is information about the data in this example:
+ `o=` This line identifies the source IP for the stream
+ `m=audio`. This identifies the file as an audio description. `20000` is the port of the stream. This line must occur before the `a` lines.
+ `c=` identifies the destination IP address. This is a unicast or multicast address.
+ `a=source-filter` identifies a filter. This line is optional. 

  In a file for an input to Elemental Live: 
  + If the line is included, Elemental Live will listen only to the source IP (10.xx.xxx.236) for packets. 
  + If the line isn't included, Elemental Live will listen to any packets on the destination IP address (239.x.x.x).

  In a file for an output: Elemental Live always includes this line in any SDP file that it creates.
+ **a=rtpmap** provides information about the audio format:
  + An example for PCM: 

    `a=rtpmap:97 L24/48000/2`

    `L24` is the number of bits per PCM audio sample. `48000` is the sample rate. `2` is the number of channels, in this example, a single stereo track.
  + An example for a Dolby Digital codec:

    `a=rtpmap:96 AM824/48000/5 a=fmtp:96 channel-order=SMPTE2110.(AES3,AES3)`

    `48000` is the sample rate. `6` is the number of AM824 subframe pairs, and must be an even number.