Add support for a=extmap-allow-mixed (RFC 8285)

Author: ibc

src/grammar.cpp

@@ -443,6 +443,22 @@ namespace sdptransform
 						}
 					},
 
+					// a=extmap-allow-mixed
+					{
+						// name:
+						"extmapAllowMixed",
+						// push:
+						"",
+						// reg:
+						std::regex("^(extmap-allow-mixed)"),
+						// names:
+						{ },
+						// types:
+						{ 's' },
+						// format:
+						"%s"
+					},
+
 					// a=crypto:1 AES_CM_128_HMAC_SHA1_80 inline:PS1uQCVeeCFCanVmcjkpPywjNWhcYD0mXXtxaVBR|2^20|1:32
 					{
 						// name:

test/data/normal.sdp

@@ -11,6 +11,7 @@ a=rtpmap:0 PCMU/8000
 a=rtpmap:96 opus/48000
 a=extmap:1 URI-toffset
 a=extmap:2/recvonly URI-gps-string
+a=extmap-allow-mixed
 a=ptime:20
 a=sendrecv
 a=candidate:0 1 UDP 2113667327 203.0.113.1 54400 typ host

test/parse.test.cpp

@@ -70,6 +70,7 @@ SCENARIO("normalSdp", "[parse]")
 			"uri"       : "URI-gps-string"
 		})"_json
 	);
+	REQUIRE(audio.at("extmapAllowMixed") == "extmap-allow-mixed");
 
 	auto& video = media[1];
 	auto videoPayloads = sdptransform::parsePayloads(video.at("payloads"));