Piggybacking simulcast id and ALR experiment id into video content type extension.

webrtc/api/video/video_content_type.cc

Index: webrtc/api/video/video_content_type.cc
diff --git a/webrtc/api/video/video_content_type.cc b/webrtc/api/video/video_content_type.cc
new file mode 100644
index 0000000000000000000000000000000000000000..7ec14951bad50762dc4554a7430290f0b032a613
--- /dev/null
+++ b/webrtc/api/video/video_content_type.cc
@@ -0,0 +1,90 @@
+/*
+ *  Copyright (c) 2017 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.
+ */
+
+#include "webrtc/api/video/video_content_type.h"
+#include "webrtc/rtc_base/checks.h"
+
+// VideoContentType stores a single byte, which is sent other the network.
+// Structure:
+//
+//  0 1 2 3 4 5 6 7
+// +---------------+
+// |r r e e e s s c|
+//
+// where:
+// r - reserved bits.
+// e - 3-bit number of an experiment group counted from 1. 0 means there's no
+// experiment ongoing.
+// s - 2-bit simulcast stream id or spatial layer, counted from 1. 0 means that
+// no simulcast information is set.
+// c - content type. 0 means real-time video, 1 means screenshare.
+//
+static const uint8_t kScreenshareBitsMask = 0x01;
+
+static const uint8_t kSimulcastShift = 1;
+static const uint8_t kSimulcastBitsMask = 0x06;  // 0b00000110
+static const uint8_t kSimulcastBitsSize = 2;
+
+static const uint8_t kExperimentShift = 3;
+static const uint8_t kExperimentBitsMask = 0x38;  // 0b00111000
+static const uint8_t kExperimentBitsSize = 3;
+
+namespace webrtc {
+const VideoContentType VideoContentType::UNSPECIFIED = VideoContentType({0});
+const VideoContentType VideoContentType::SCREENSHARE = VideoContentType({1});
+
+VideoContentType::operator uint8_t() const {
+  return content_type;
+}
+
+uint8_t VideoContentType::operator=(uint8_t value) {
+  content_type = value;
+  return value;
+}
+
+bool VideoContentType::operator==(const VideoContentType& other) {
+  return content_type == other.content_type;
+}
+
+bool VideoContentType::operator==(uint8_t value) {
+  return content_type == value;
+}
+
+void VideoContentType::SetExperimentId(uint8_t experiment_id) {
+  // Store in bits 3-5.
+  RTC_DCHECK(experiment_id < (1 << kExperimentBitsSize));
+  content_type = (content_type & ~kExperimentBitsMask) |
+                 ((experiment_id << kExperimentShift) & kExperimentBitsMask);
+}
+
+void VideoContentType::SetSimulcastId(uint8_t simulcast_id) {
+  // Store in bits 1-2.
+  RTC_DCHECK(simulcast_id < (1 << kSimulcastBitsSize));
+  content_type = (content_type & ~kSimulcastBitsMask) |
+                 ((simulcast_id << kSimulcastShift) & kSimulcastBitsMask);
+}
+
+uint8_t VideoContentType::GetExperimentId() const {
+  return (content_type & kExperimentBitsMask) >> kExperimentShift;
+}
+
+uint8_t VideoContentType::GetSimulcastId() const {
+  return (content_type & kSimulcastBitsMask) >> kSimulcastShift;
+}
+
+bool VideoContentType::IsValidContentType(uint8_t value) {
+  // Any 6-bit value is allowed.
+  return value < (1 << 6);
+}
+
+bool VideoContentType::IsScreenshare() const {
+  return (content_type & kScreenshareBitsMask) > 0;
+}
+}  // namespace webrtc