Add support for a forced software encoder fallback.

webrtc/media/engine/videoencodersoftwarefallbackwrapper.h

Index: webrtc/media/engine/videoencodersoftwarefallbackwrapper.h
diff --git a/webrtc/media/engine/videoencodersoftwarefallbackwrapper.h b/webrtc/media/engine/videoencodersoftwarefallbackwrapper.h
index 61c1a11c8d32e798b043c033c3cbecde17b91df8..2003c2b9bff8e9ad53f5ab5dc5461af1f0eedbef 100644
--- a/webrtc/media/engine/videoencodersoftwarefallbackwrapper.h
+++ b/webrtc/media/engine/videoencodersoftwarefallbackwrapper.h
@@ -46,9 +46,27 @@ class VideoEncoderSoftwareFallbackWrapper : public VideoEncoder {
   ScalingSettings GetScalingSettings() const override;
   const char *ImplementationName() const override;
 
+  // If |forced_fallback_enabled_| is true and the encoded resolution
+  // is <= |max_pixels|:
+  // The forced fallback is enabled if the target bitrate is below |low_kbps|
+  // for more than |min_low_ms|. If the bitrate is above |high_kbps|, the forced

[sprang_webrtc, 2017/08/07 08:59:12]

Does same time limit apply for high_kbps?

[åsapersson, 2017/08/08 10:40:54]

No, updated comment.

+  // fallback is disabled.
+  struct ForcedFallbackParams {
+    rtc::Optional<int64_t> start_ms;

[brandtr, 2017/08/04 11:16:23]

IIUC, start_ms is the timestamp when we go below |low_kbps| ?

[åsapersson, 2017/08/08 10:40:54]

Added comment.

[brandtr, 2017/08/09 09:05:02]

Thanks. It's easier to understand now.

+    uint32_t low_kbps = 100;
+    uint32_t high_kbps = 150;
+    int64_t min_low_ms = 10000;
+    const int max_pixels = 76800;  // 320 * 240

[brandtr, 2017/08/04 11:16:23]

Maybe remove comment and write max_pixels = 320 * 240 ?

[åsapersson, 2017/08/08 10:40:54]

Done.

+  };
+
  private:
   bool InitFallbackEncoder();
 
+  bool StartForcedFallback();
+  bool TryReleaseForcedFallbackEncoder();
+  bool TryReInitForcedFallbackEncoder();
+  void ValidateSettingsForForcedFallback();
+
   // Settings used in the last InitEncode call and used if a dynamic fallback to
   // software is required.
   VideoCodec codec_settings_;
@@ -71,6 +89,9 @@ class VideoEncoderSoftwareFallbackWrapper : public VideoEncoder {
   std::unique_ptr<webrtc::VideoEncoder> fallback_encoder_;
   std::string fallback_implementation_name_;
   EncodedImageCallback* callback_;
+
+  bool forced_fallback_enabled_;

[brandtr, 2017/08/04 11:16:23]

How about |forced_fallback_possible_|? This member only shows if we can do the
forced fallback, not if we have actually done it.

[åsapersson, 2017/08/08 10:40:54]

Done.

+  ForcedFallbackParams forced_fallback_;
 };
 
 }  // namespace webrtc