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

webrtc/modules/video_coding/generic_encoder.cc

 /*
 *  Copyright (c) 2012 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/modules/video_coding/generic_encoder.h"
 
 #include <vector>
 
 #include "webrtc/api/video/i420_buffer.h"
+#include "webrtc/modules/pacing/alr_detector.h"

[sprang_webrtc, 2017/07/26 14:13:43]

Don't add dependency between modules. If we need this only for the experiment
name, then move that to some shared lower level dependency instead.

[ilnik, 2017/07/26 14:49:48]

We also need |AlrDetector::ParseAlrSettingsFromFieldTrial()|
This is now non trivial logic. If you have time, could you please move it and
experiment names out of that file somewhere else?

 #include "webrtc/modules/video_coding/encoded_frame.h"
 #include "webrtc/modules/video_coding/media_optimization.h"
 #include "webrtc/rtc_base/checks.h"
 #include "webrtc/rtc_base/logging.h"
 #include "webrtc/rtc_base/optional.h"
 #include "webrtc/rtc_base/timeutils.h"
 #include "webrtc/rtc_base/trace_event.h"
+#include "webrtc/system_wrappers/include/field_trial.h"
 
 namespace webrtc {
 
 VCMGenericEncoder::VCMGenericEncoder(
     VideoEncoder* encoder,
     VCMEncodedFrameCallback* encoded_frame_callback,
     bool internal_source)
     : encoder_(encoder),
       vcm_encoded_frame_callback_(encoded_frame_callback),
       internal_source_(internal_source),
@@ skipping 254 matching lines @@
 
   // If encode start is not available that means that encoder uses internal
   // source. In that case capture timestamp may be from a different clock with a
   // drift relative to rtc::TimeMillis(). We can't use it for Timing frames,
   // because to being sent in the network capture time required to be less than
   // all the other timestamps.
   if (is_timing_frame && encode_start_ms) {
     encoded_image.SetEncodeTime(*encode_start_ms, rtc::TimeMillis());
   }
 
+  // Piggyback ALR experiment group id and simulcast id into the content type.
+  uint8_t experiment_id = 0;
+  rtc::Optional<AlrDetector::AlrExperimentSettings> experiment_settings =
+      AlrDetector::ParseAlrSettingsFromFieldTrial();
+  if (experiment_settings) {
+    // 0 would mean no experiment, therefore adding 1. It will be subtracted at
+    // the receive side before reporting fake field trial.
+    experiment_id = experiment_settings->group_id + 1;
+  }
+
+  // TODO(ilnik): This will force content type extension to be present even
+  // for realtime video. At the expense of miniscule overhead we will get
+  // sliced receive statistics.
+  encoded_image.content_type_.SetExperimentId(experiment_id);
+  // We number simulcast streams from 1 on the network.
+  encoded_image.content_type_.SetSimulcastId(
+      static_cast<uint8_t>(simulcast_svc_idx + 1));
+
   Result result = post_encode_callback_->OnEncodedImage(
       encoded_image, codec_specific, fragmentation_header);
   if (result.error != Result::OK)
     return result;
 
   if (media_opt_) {
     media_opt_->UpdateWithEncodedData(encoded_image);
     if (internal_source_) {
       // Signal to encoder to drop next frame.
       result.drop_next_frame = media_opt_->DropFrame();
     }
   }
   return result;
 }
 
 }  // namespace webrtc