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

webrtc/modules/rtp_rtcp/source/rtp_header_extensions.cc

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 178 matching lines @@
   RTC_DCHECK_LE(0, playout_delay.min_ms);
   RTC_DCHECK_LE(playout_delay.min_ms, playout_delay.max_ms);
   RTC_DCHECK_LE(playout_delay.max_ms, kMaxMs);
   // Convert MS to value to be sent on extension header.
   uint32_t min_delay = playout_delay.min_ms / kGranularityMs;
   uint32_t max_delay = playout_delay.max_ms / kGranularityMs;
   ByteWriter<uint32_t, 3>::WriteBigEndian(data, (min_delay << 12) | max_delay);
   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 VideoContentTypeExtension::kId;
+constexpr uint8_t VideoContentTypeExtension::kValueSizeBytes;
+constexpr const char* VideoContentTypeExtension::kUri;
+
+bool VideoContentTypeExtension::Parse(const uint8_t* data,
+                                      VideoContentType* content_type) {
+  *content_type = static_cast<VideoContentType>(data[0]);
+  return true;
+}
+
+bool VideoContentTypeExtension::Write(uint8_t* data,
+                                      VideoContentType content_type) {
+  data[0] = static_cast<uint8_t>(content_type);
+  return true;
+}
+
 }  // namespace webrtc