Update sink wants with ranges for both pixel count and frame rate.

webrtc/media/base/videobroadcaster.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 55 matching lines @@
     if (sink_pair.wants.black_frames) {
       sink_pair.sink->OnFrame(webrtc::VideoFrame(
           GetBlackFrameBuffer(frame.width(), frame.height()), frame.rotation(),
           frame.timestamp_us()));
     } else {
       sink_pair.sink->OnFrame(frame);
     }
   }
 }
 
+void VideoBroadcaster::MergeWantsRange(
+    rtc::Optional<rtc::VideoSinkWants::Range>* merged_range,
+    const rtc::VideoSinkWants::Range& item) {
+  if (!*merged_range) {
+    merged_range->emplace(item);
+    return;
+  }

[nisse-webrtc, 2017/02/21 09:33:59]

I think this is in the right direction. Might be even prettier with a
non-destructive function like

  Range Intersect(const Range& a, const Range& b);

(And can we find a better name than Range for an object which is a range + a
target value? For lack of better ideas, maybe RangeWant ?).

[sprang_webrtc, 2017/02/21 09:42:38]

I think I'll revisit this when/if removing the Optional part.
RangeWant could work... or maybe TargetRange ? :)

+
+  // Merge the constraints if there are more than one wants. Lowest max
+  // will set the max cap and the highest min will set the min cap, as
+  // these are pretty hard bounds. For now chose the min of the targets as
+  // well, erring of the side of caution so that we don't overutilize some
+  // resource.
+  // TODO(sprang): Consider using median of targets?
+  (*merged_range)->max = std::min<uint32_t>((*merged_range)->max, item.max);
+  (*merged_range)->target =
+      std::min<uint32_t>((*merged_range)->target, item.target);
+  (*merged_range)->min = std::max<uint32_t>((*merged_range)->min, item.min);
+
+  // Make sure there is no contradiction in the merged wants.
+  (*merged_range)->min =
+      std::min<uint32_t>((*merged_range)->min, (*merged_range)->max);
+  (*merged_range)->target =
+      std::min<uint32_t>((*merged_range)->target, (*merged_range)->max);
+  (*merged_range)->target =
+      std::max<uint32_t>((*merged_range)->target, (*merged_range)->min);
+}
+
 void VideoBroadcaster::UpdateWants() {
   RTC_DCHECK(thread_checker_.CalledOnValidThread());
 
   VideoSinkWants wants;
   wants.rotation_applied = false;
   for (auto& sink : sink_pairs()) {
     // wants.rotation_applied == ANY(sink.wants.rotation_applied)
-    if (sink.wants.rotation_applied) {
+    if (sink.wants.rotation_applied)
       wants.rotation_applied = true;
-    }
-    // wants.max_pixel_count == MIN(sink.wants.max_pixel_count)
-    if (sink.wants.max_pixel_count &&
-        (!wants.max_pixel_count ||
-         (*sink.wants.max_pixel_count < *wants.max_pixel_count))) {
-      wants.max_pixel_count = sink.wants.max_pixel_count;
-    }
-    // Select the minimum requested target_pixel_count, if any, of all sinks so
-    // that we don't over utilize the resources for any one.
-    // TODO(sprang): Consider using the median instead, since the limit can be
-    // expressed by max_pixel_count.
-    if (sink.wants.target_pixel_count &&
-        (!wants.target_pixel_count ||
-         (*sink.wants.target_pixel_count < *wants.target_pixel_count))) {
-      wants.target_pixel_count = sink.wants.target_pixel_count;
-    }
+
+    if (sink.wants.pixel_count)
+      MergeWantsRange(&wants.pixel_count, *sink.wants.pixel_count);
+    if (sink.wants.framerate_fps_)
+      MergeWantsRange(&wants.framerate_fps_, *sink.wants.framerate_fps_);
   }
 
-  if (wants.max_pixel_count && wants.target_pixel_count &&
-      *wants.target_pixel_count >= *wants.max_pixel_count) {
-    wants.target_pixel_count = wants.max_pixel_count;
-  }
   current_wants_ = wants;
 }
 
 const rtc::scoped_refptr<webrtc::VideoFrameBuffer>&
 VideoBroadcaster::GetBlackFrameBuffer(int width, int height) {
   if (!black_frame_buffer_ || black_frame_buffer_->width() != width ||
       black_frame_buffer_->height() != height) {
     rtc::scoped_refptr<webrtc::I420Buffer> buffer =
         webrtc::I420Buffer::Create(width, height);
     webrtc::I420Buffer::SetBlack(buffer.get());
     black_frame_buffer_ = buffer;
   }
 
   return black_frame_buffer_;
 }
 
 }  // namespace rtc