Add support for a forced software encoder fallback.

webrtc/media/engine/videoencodersoftwarefallbackwrapper.h

 /*
  *  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 31 matching lines @@
   int32_t SetChannelParameters(uint32_t packet_loss, int64_t rtt) override;
   int32_t SetRateAllocation(const BitrateAllocation& bitrate_allocation,
                             uint32_t framerate) override;
   bool SupportsNativeHandle() const override;
   ScalingSettings GetScalingSettings() const override;
   const char *ImplementationName() const override;
 
  private:
   bool InitFallbackEncoder();
 
+  // If |forced_fallback_possible_| is true:
+  // The forced fallback is requested if the target bitrate is below |low_kbps|
+  // for more than |min_low_ms| and the input video resolution is not larger
+  // than |kMaxPixels|.
+  // If the bitrate is above |high_kbps|, the forced fallback is requested to
+  // immediately be stopped.
+  class ForcedFallbackParams {
+   public:
+    bool Start(uint32_t kbps, const VideoCodec& codec);

[brandtr, 2017/08/09 09:05:03]

How about naming these ShouldStart and ShouldStop ?

[åsapersson, 2017/08/09 09:50:36]

Done.

+    bool Stop(uint32_t kbps) const { return kbps >= high_kbps; }
+    void Reset() { start_ms.reset(); }
+    bool IsValid(const VideoCodec& codec) const {
+      return codec.width * codec.height <= kMaxPixels;
+    }
+    rtc::Optional<int64_t> start_ms;  // Set when bitrate is below |low_kbps|.
+    uint32_t low_kbps = 100;
+    uint32_t high_kbps = 150;
+    int64_t min_low_ms = 10000;
+    const int kMaxPixels = 320 * 240;
+  };
+
+  bool RequestForcedFallback();
+  bool TryReleaseForcedFallbackEncoder();
+  bool TryReInitForcedFallbackEncoder();
+  void ValidateSettingsForForcedFallback();
+  bool IsForcedFallbackActive() const;
+
   // Settings used in the last InitEncode call and used if a dynamic fallback to
   // software is required.
   VideoCodec codec_settings_;
   int32_t number_of_cores_;
   size_t max_payload_size_;
 
   // The last bitrate/framerate set, and a flag for noting they are set.
   bool rates_set_;
   BitrateAllocation bitrate_allocation_;
   uint32_t framerate_;
 
   // The last channel parameters set, and a flag for noting they are set.
   bool channel_parameters_set_;
   uint32_t packet_loss_;
   int64_t rtt_;
 
   const cricket::VideoCodec codec_;
   webrtc::VideoEncoder* const encoder_;
 
   std::unique_ptr<webrtc::VideoEncoder> fallback_encoder_;
   std::string fallback_implementation_name_;
   EncodedImageCallback* callback_;
+
+  bool forced_fallback_possible_;
+  ForcedFallbackParams forced_fallback_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MEDIA_ENGINE_VIDEOENCODERSOFTWAREFALLBACKWRAPPER_H_