Introduction
If we talk about Streaming Media Industry then there are lot of protocols which take place like RTMP, RTSP, SRT, HLS, HDS and MPEG DASH etc. All of these protocols we have explained earlier in our previous articles.
So today in this article we are going to describe about SDP Protocol in brief with example.
What Is SDP For Streaming Media ?
SDP is called the Session Description Protocol. SDP was introduced by IETF as RFC 4566. Where IETF represents Internet Engineering Task Force.
So SDP is a IETF standard for Streaming Media. SDP is encapsulated with SIP (Session Initialization Protocol ).
Session Description Protocol is used to define all the parameters needed to start a streaming media session for all endpoints. Where these parameters can be Protocol Version, Origin Name and Description of Media etc.
SDP itself never transfer the media files while it defines parameters needed to transfer it.
A SDP File contains all of these parameters for streaming session.
If you want to connect with a streaming server which is streaming MPEG2 TS you normally do not need any SDP File. Because you can use the Uniform Resource Identifier like,
rtp://{Server-IP}:{Port}
udp://{Server-IP}:{Port}
But in case if you want to have more control on the streaming server then you can go for SDP File like,
name_sdp_file.sdp (For Root Directory)
http://my_server/name_sdp_file.sdp (For SDP In remote server)
Lets now discuss about how to define SDP File.
Explain Me What Is RTMP Protocol ?
What Is SDP File Format ?
As Shown Above in the figure SDP File Format is divided into two sections Which are described below,
(1) Session Description
In this section we need to define only session related parameters. Which can be four things. These are Version of the protocol, Origin and Session ID, Name Of the Session and Time for this session etc.
But for a SDP File below mentioned four things are mandatory to define,
v = Version Of Protocol
o = Origin Of Session
s = Name Of Session
t = time of session
(2) Media Description
This section of SDP File contain all media related information which is implementing in the streaming media session.
Where we need to define the type of media , its port number, Its format and what kind of protocol we are going to use for this media. We can also define RTP Payload Format.
We are mentioning below mandatory things which we need to define in Media Description,
m = [media]
Type Of Your Media
Port Number
Transport Protocol
Media Format
A Complete SDP File Format With Optional & Mandatory Fields Is Described Below,
Session Format
v = protocol Version
o = Origin
s = Name Of Session
i = Information Of Session
u = URI
e = Email Address
p = Phone Number
c = Connection Information
b = bandwidth inforamtion
t = time description
r = repeat information
z = timezone
k = key of encryption
a = attribute
Media Format
m = description of media
i = information of media
c = information of connection
b = information of bandwidth
k = key of encryption
a = attribute
Example Of SDP File Format
As shown above in the file there is version number which is 0 here. Then after “o” is indicating the origin name server.
“s” it indicates the name of the session. “c” is indicating the multicast IP address of streaming server which is 239.192.33.44.
“t” it is defines the session start time and end time too. So all of these fields which we discussed yet comes under Session Description.
“m” it comes under media descritpion. Where media type is Video. 1024 is the streaming port. UDP is format of streaming media. This format can be RTP/AVP.
v=0
o=HeadendInfoStreamer 5236523123 5487920126 IN IP4 11.12.13.14
s=HeadendInfoStreamer video Session
c=IN IP4 (Streaming_Serer_IP)
t=0 0
m=video (streaming_port) (streaming_format) 33
Conclusion
Session Description Protocol defines the all the parameters of a streaming media session before starting it. It is just like video conferencing in corporate.
It defines various things of session like time of session , name of session, type of media file with port number and its format too. All of these things are contained in SDP file. Session Description Protocol can also be used for to start audio session.
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reference : ietf
