Move kMinPixelsPerFrame constant in VideoStreamEncoder to VideoEncoder::ScalingSettings.

Make it possible for forced VP8 SW fallback encoder to set min_pixels_per_frame via GetScalingSettings().

Add a min required resolution (in addition to bitrate) before releasing forced SW fallback.

BUG=webrtc:6634

Review-Url: https://codereview.webrtc.org/3000693003
Cr-Commit-Position: refs/heads/master@{#19390}
diff --git a/webrtc/modules/video_coding/BUILD.gn b/webrtc/modules/video_coding/BUILD.gn
index 52d0327..ef6c262 100644
--- a/webrtc/modules/video_coding/BUILD.gn
+++ b/webrtc/modules/video_coding/BUILD.gn
@@ -464,6 +464,7 @@
       "../../api:video_frame_api",
       "../../common_video:common_video",
       "../../rtc_base:rtc_base_approved",
+      "../../test:field_trial",
       "../../test:test_support",
       "../../test:video_test_common",
       "../video_capture",
diff --git a/webrtc/modules/video_coding/codecs/vp8/test/vp8_impl_unittest.cc b/webrtc/modules/video_coding/codecs/vp8/test/vp8_impl_unittest.cc
index 7e04167..d987187 100644
--- a/webrtc/modules/video_coding/codecs/vp8/test/vp8_impl_unittest.cc
+++ b/webrtc/modules/video_coding/codecs/vp8/test/vp8_impl_unittest.cc
@@ -20,9 +20,11 @@
 #include "webrtc/rtc_base/checks.h"
 #include "webrtc/rtc_base/optional.h"
 #include "webrtc/rtc_base/timeutils.h"
+#include "webrtc/test/field_trial.h"
 #include "webrtc/test/frame_utils.h"
 #include "webrtc/test/gtest.h"
 #include "webrtc/test/testsupport/fileutils.h"
+#include "webrtc/test/video_codec_settings.h"
 
 namespace webrtc {
 
@@ -39,6 +41,10 @@
 constexpr uint32_t kTestTimestamp = 123;
 constexpr int64_t kTestNtpTimeMs = 456;
 constexpr uint32_t kTimestampIncrementPerFrame = 3000;
+constexpr int kNumCores = 1;
+constexpr size_t kMaxPayloadSize = 1440;
+constexpr int kMinPixelsPerFrame = 12345;
+constexpr int kDefaultMinPixelsPerFrame = 320 * 180;
 
 }  // namespace
 
@@ -143,6 +149,10 @@
 
 class TestVp8Impl : public ::testing::Test {
  protected:
+  TestVp8Impl() : TestVp8Impl("") {}
+  explicit TestVp8Impl(const std::string& field_trials)
+      : override_field_trials_(field_trials) {}
+
   virtual void SetUp() {
     encoder_.reset(VP8Encoder::Create());
     decoder_.reset(VP8Decoder::Create());
@@ -190,9 +200,11 @@
     codec_settings_.VP8()->tl_factory = &tl_factory_;
     codec_settings_.VP8()->numberOfTemporalLayers = 1;
 
+    EXPECT_EQ(
+        WEBRTC_VIDEO_CODEC_OK,
+        encoder_->InitEncode(&codec_settings_, kNumCores, kMaxPayloadSize));
     EXPECT_EQ(WEBRTC_VIDEO_CODEC_OK,
-              encoder_->InitEncode(&codec_settings_, 1, 1440));
-    EXPECT_EQ(WEBRTC_VIDEO_CODEC_OK, decoder_->InitDecode(&codec_settings_, 1));
+              decoder_->InitDecode(&codec_settings_, kNumCores));
   }
 
   size_t WaitForEncodedFrame() const {
@@ -228,6 +240,7 @@
   const int kWidth = 172;
   const int kHeight = 144;
 
+  test::ScopedFieldTrials override_field_trials_;
   std::unique_ptr<Vp8UnitTestEncodeCompleteCallback> encode_complete_callback_;
   std::unique_ptr<Vp8UnitTestDecodeCompleteCallback> decode_complete_callback_;
   std::unique_ptr<uint8_t[]> source_buffer_;
@@ -266,12 +279,13 @@
                                         codec_settings_.maxFramerate));
 
   EXPECT_EQ(WEBRTC_VIDEO_CODEC_OK,
-            encoder_->InitEncode(&codec_settings_, 1, 1440));
+            encoder_->InitEncode(&codec_settings_, kNumCores, kMaxPayloadSize));
 
   // Decoder parameter tests.
   // Calls before InitDecode().
   EXPECT_EQ(WEBRTC_VIDEO_CODEC_OK, decoder_->Release());
-  EXPECT_EQ(WEBRTC_VIDEO_CODEC_OK, decoder_->InitDecode(&codec_settings_, 1));
+  EXPECT_EQ(WEBRTC_VIDEO_CODEC_OK,
+            decoder_->InitDecode(&codec_settings_, kNumCores));
 }
 
 // We only test the encoder here, since the decoded frame rotation is set based
@@ -374,7 +388,7 @@
   // Override default settings.
   codec_settings_.VP8()->numberOfTemporalLayers = 2;
   EXPECT_EQ(WEBRTC_VIDEO_CODEC_OK,
-            encoder_->InitEncode(&codec_settings_, 1, 1440));
+            encoder_->InitEncode(&codec_settings_, kNumCores, kMaxPayloadSize));
 
   // Temporal layer 0.
   EXPECT_EQ(WEBRTC_VIDEO_CODEC_OK,
@@ -410,7 +424,7 @@
   // Reinit.
   EXPECT_EQ(WEBRTC_VIDEO_CODEC_OK, encoder_->Release());
   EXPECT_EQ(WEBRTC_VIDEO_CODEC_OK,
-            encoder_->InitEncode(&codec_settings_, 1, 1440));
+            encoder_->InitEncode(&codec_settings_, kNumCores, kMaxPayloadSize));
 
   // Temporal layer 0.
   input_frame_->set_timestamp(input_frame_->timestamp() +
@@ -445,4 +459,46 @@
                   1);
 }
 
+TEST_F(TestVp8Impl, ScalingDisabledIfAutomaticResizeOff) {
+  webrtc::test::CodecSettings(kVideoCodecVP8, &codec_settings_);
+  codec_settings_.VP8()->tl_factory = &tl_factory_;
+  codec_settings_.VP8()->automaticResizeOn = false;
+
+  EXPECT_EQ(WEBRTC_VIDEO_CODEC_OK,
+            encoder_->InitEncode(&codec_settings_, kNumCores, kMaxPayloadSize));
+  VideoEncoder::ScalingSettings settings = encoder_->GetScalingSettings();
+  EXPECT_FALSE(settings.enabled);
+}
+
+TEST_F(TestVp8Impl, ScalingEnabledIfAutomaticResizeOn) {
+  webrtc::test::CodecSettings(kVideoCodecVP8, &codec_settings_);
+  codec_settings_.VP8()->tl_factory = &tl_factory_;
+  codec_settings_.VP8()->automaticResizeOn = true;
+
+  EXPECT_EQ(WEBRTC_VIDEO_CODEC_OK,
+            encoder_->InitEncode(&codec_settings_, kNumCores, kMaxPayloadSize));
+  VideoEncoder::ScalingSettings settings = encoder_->GetScalingSettings();
+  EXPECT_TRUE(settings.enabled);
+  EXPECT_EQ(kDefaultMinPixelsPerFrame, settings.min_pixels_per_frame);
+}
+
+class TestVp8ImplWithForcedFallbackEnabled : public TestVp8Impl {
+ public:
+  TestVp8ImplWithForcedFallbackEnabled()
+      : TestVp8Impl("WebRTC-VP8-Forced-Fallback-Encoder/Enabled-1,2,3," +
+                    std::to_string(kMinPixelsPerFrame) + "/") {}
+};
+
+TEST_F(TestVp8ImplWithForcedFallbackEnabled, MinPixelsPerFrameConfigured) {
+  webrtc::test::CodecSettings(kVideoCodecVP8, &codec_settings_);
+  codec_settings_.VP8()->tl_factory = &tl_factory_;
+  codec_settings_.VP8()->automaticResizeOn = true;
+
+  EXPECT_EQ(WEBRTC_VIDEO_CODEC_OK,
+            encoder_->InitEncode(&codec_settings_, kNumCores, kMaxPayloadSize));
+  VideoEncoder::ScalingSettings settings = encoder_->GetScalingSettings();
+  EXPECT_TRUE(settings.enabled);
+  EXPECT_EQ(kMinPixelsPerFrame, settings.min_pixels_per_frame);
+}
+
 }  // namespace webrtc
diff --git a/webrtc/modules/video_coding/codecs/vp8/vp8_impl.cc b/webrtc/modules/video_coding/codecs/vp8/vp8_impl.cc
index 3f9f879..5933073 100644
--- a/webrtc/modules/video_coding/codecs/vp8/vp8_impl.cc
+++ b/webrtc/modules/video_coding/codecs/vp8/vp8_impl.cc
@@ -42,6 +42,8 @@
 
 const char kVp8PostProcArmFieldTrial[] = "WebRTC-VP8-Postproc-Arm";
 const char kVp8GfBoostFieldTrial[] = "WebRTC-VP8-GfBoost";
+const char kVp8ForceFallbackEncoderFieldTrial[] =
+    "WebRTC-VP8-Forced-Fallback-Encoder";
 
 const int kTokenPartitions = VP8_ONE_TOKENPARTITION;
 enum { kVp8ErrorPropagationTh = 30 };
@@ -110,6 +112,31 @@
   return num_disabled;
 }
 
+rtc::Optional<int> GetForcedFallbackMinPixelsFromFieldTrialGroup() {
+  if (!webrtc::field_trial::IsEnabled(kVp8ForceFallbackEncoderFieldTrial))
+    return rtc::Optional<int>();
+
+  std::string group =
+      webrtc::field_trial::FindFullName(kVp8ForceFallbackEncoderFieldTrial);
+  if (group.empty())
+    return rtc::Optional<int>();
+
+  int low_kbps;
+  int high_kbps;
+  int min_low_ms;
+  int min_pixels;
+  if (sscanf(group.c_str(), "Enabled-%d,%d,%d,%d", &low_kbps, &high_kbps,
+             &min_low_ms, &min_pixels) != 4) {
+    return rtc::Optional<int>();
+  }
+
+  if (min_low_ms <= 0 || min_pixels <= 0 || low_kbps <= 0 ||
+      high_kbps <= low_kbps) {
+    return rtc::Optional<int>();
+  }
+  return rtc::Optional<int>(min_pixels);
+}
+
 bool GetGfBoostPercentageFromFieldTrialGroup(int* boost_percentage) {
   std::string group = webrtc::field_trial::FindFullName(kVp8GfBoostFieldTrial);
   if (group.empty())
@@ -181,6 +208,7 @@
 
 VP8EncoderImpl::VP8EncoderImpl()
     : use_gf_boost_(webrtc::field_trial::IsEnabled(kVp8GfBoostFieldTrial)),
+      min_pixels_per_frame_(GetForcedFallbackMinPixelsFromFieldTrialGroup()),
       encoded_complete_callback_(nullptr),
       inited_(false),
       timestamp_(0),
@@ -935,6 +963,10 @@
   const bool enable_scaling = encoders_.size() == 1 &&
                               configurations_[0].rc_dropframe_thresh > 0 &&
                               codec_.VP8().automaticResizeOn;
+  if (enable_scaling && min_pixels_per_frame_) {
+    return VideoEncoder::ScalingSettings(enable_scaling,
+                                         *min_pixels_per_frame_);
+  }
   return VideoEncoder::ScalingSettings(enable_scaling);
 }
 
diff --git a/webrtc/modules/video_coding/codecs/vp8/vp8_impl.h b/webrtc/modules/video_coding/codecs/vp8/vp8_impl.h
index 7b5e000..30a4a1a 100644
--- a/webrtc/modules/video_coding/codecs/vp8/vp8_impl.h
+++ b/webrtc/modules/video_coding/codecs/vp8/vp8_impl.h
@@ -94,6 +94,7 @@
   uint32_t MaxIntraTarget(uint32_t optimal_buffer_size);
 
   const bool use_gf_boost_;
+  const rtc::Optional<int> min_pixels_per_frame_;
 
   EncodedImageCallback* encoded_complete_callback_;
   VideoCodec codec_;