stoth68000 / sdp_parser

A session description protocol (SDP - RFC4566) parser

sdp_parser

A session description protocol parser (RFC4566 - SDP).

The motivation for writing this parser was to parse SDP messges for the SMPTE ST 2110-20 protocol (Professional Media over Managed IP networks: Uncompressed Active Video). As such, it only parses SDP fields which are essential for defining a video media session, and does so with some constraints.

An example SDP

v=0
o=- 123456 11 IN IP4 192.168.100.2
s=Example of a SMPTE ST2110-20 signal
i=this example is for 720p video at 59.94
t=0 0
a=recvonly
a=group:DUP primary secondary
m=video 50000 RTP/AVP 112
c=IN IP4 239.100.9.10/32
a=source-filter:incl IN IP4 239.100.9.10 192.168.100.2
a=rtpmap:112 raw/90000
a=fmtp:112 sampling=YCbCr-4:2:2; width=1280; height=720; exactframerate=60000/1001; depth=10; TCS=SDR; colorimetry=BT709; PM=2110GPM; TP=2110TPN; SSN=ST2110-20:2017;
a=ts-refclk:ptp=IEEE1588-2008:39-A7-94-FF-FE-07-CB-D0:37
a=mediaclk:direct=0
a=mid:primary
m=video 50020 RTP/AVP 112
c=IN IP4 239.101.9.10/32
a=source-filter:incl IN IP4 239.101.9.10 192.168.101.2
a=rtpmap:112 raw/90000
a=fmtp:112 sampling=YCbCr-4:2:2; width=1280; height=720; exactframerate=60000/1001; depth=10; TCS=SDR; colorimetry=BT709; PM=2110GPM; TP=2110TPN; SSN=ST2110-20:2017;
a=ts-refclk:ptp=IEEE1588-2008:39-A7-94-FF-FE-07-CB-D0:37
a=mediaclk:direct=0
a=mid:secondary

This SDP defines two streams with the same parameters received at 239.100.9.10:50000 and at 239.101.9.10:50020 (this is clearly an old version of 2110-10 since the required TP= parameter in the a=fmtp attribute is missing).

A few notes

• Highlighted in bold are the clauses which get parsed by my parser (a.k.a supported fields)
• Supported fields are parsed as defined in RFC4566 (order of appearance/required/optional/format/etc…)
• All non-supported fields can be omitted from the SDP file – the parser will not complain even if they're defined as required by RFC4566
• For any non-supported field of the form x=... the parser only asserts that x is a field defined in RFC4566. If it is not, parsing will return an error
• media-level attribute a=fmtp:<fmt> <params>, has its params fully parsed according to 2110-20 and 2110-21, section 8 (according to the versions of the spec I have)
• The parser can easily be extended as required