Add content type information to encoded images and corresponding rtp extension header

webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc

Index: webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc b/webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc
index 167f29ee956ed5000c0da40007aa3a1867e954d4..e115b766ab019431e28cbacb899ea17103405770 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc
@@ -196,4 +196,28 @@ bool PlayoutDelayLimits::Write(uint8_t* data,
   return true;
 }
 
+// Video Content Type.
+//
+// E.g. default video or screenshare.
+//
+//    0                   1
+//    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//   |  ID   | len=0 | Content type  |
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+constexpr RTPExtensionType VideoContentType::kId;
+constexpr uint8_t VideoContentType::kValueSizeBytes;
+constexpr const char* VideoContentType::kUri;
+
+bool VideoContentType::Parse(const uint8_t* data,
+                             VideoContentTypeId* content_type) {
+  *content_type = static_cast<VideoContentTypeId>(data[0]);
+  return true;
+}
+
+bool VideoContentType::Write(uint8_t* data, VideoContentTypeId content_type) {
+  data[0] = content_type;
+  return true;
+}
+
 }  // namespace webrtc