Make RtpEncodingParameters to not reverse active flags order

Bug: webrtc:11319
Change-Id: If63db02d282ee622c12405f85c0fbae1ba13fcb2
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/168196
Reviewed-by: Florent Castelli <orphis@webrtc.org>
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30459}

media/engine/webrtc_video_engine.cc

@@ -2117,6 +2117,17 @@ void WebRtcVideoChannel::WebRtcVideoSendStream::UpdateSendState() {
     for (size_t i = 0; i < num_layers; ++i) {
       active_layers[i] = IsLayerActive(rtp_parameters_.encodings[i]);
     }
+    if (parameters_.encoder_config.number_of_streams == 1 &&
+        rtp_parameters_.encodings.size() > 1) {
+      // SVC is used.
+      // The only present simulcast layer should be active if any of the
+      // configured SVC layers is active.
+      bool is_active = false;
+      for (size_t i = 0; i < rtp_parameters_.encodings.size(); ++i) {
+        is_active |= rtp_parameters_.encodings[i].active;
+      }
+      active_layers[0] = is_active;
+    }
     // This updates what simulcast layers are sending, and possibly starts
     // or stops the VideoSendStream.
     stream_->UpdateActiveSimulcastLayers(active_layers);

modules/video_coding/video_codec_initializer.cc

@@ -156,6 +156,9 @@ VideoCodec VideoCodecInitializer::VideoEncoderConfigToVideoCodec(
       break;
     }
     case kVideoCodecVP9: {
+      // Force the first stream to always be active.
+      video_codec.simulcastStream[0].active = codec_active;
+
       if (!config.encoder_specific_settings) {
         *video_codec.VP9() = VideoEncoder::GetDefaultVp9Settings();
       }
@@ -197,7 +200,7 @@ VideoCodec VideoCodecInitializer::VideoEncoderConfigToVideoCodec(
              spatial_idx < config.simulcast_layers.size() &&
              spatial_idx < spatial_layers.size();
              ++spatial_idx) {
-          spatial_layers[spatial_layers.size() - spatial_idx - 1].active =
+          spatial_layers[spatial_idx].active =
               config.simulcast_layers[spatial_idx].active;
         }
       }

modules/video_coding/video_codec_initializer_unittest.cc

@@ -351,14 +351,14 @@ TEST_F(VideoCodecInitializerTest, Vp9DeactivateLayers) {
   EXPECT_TRUE(codec_out_.spatialLayers[2].active);
 
   // Deactivate top layer.
-  config_.simulcast_layers[0].active = false;
+  config_.simulcast_layers[2].active = false;
   EXPECT_TRUE(InitializeCodec());
   EXPECT_TRUE(codec_out_.spatialLayers[0].active);
   EXPECT_TRUE(codec_out_.spatialLayers[1].active);
   EXPECT_FALSE(codec_out_.spatialLayers[2].active);
 
   // Deactivate middle layer.
-  config_.simulcast_layers[0].active = true;
+  config_.simulcast_layers[2].active = true;
   config_.simulcast_layers[1].active = false;
   EXPECT_TRUE(InitializeCodec());
   EXPECT_TRUE(codec_out_.spatialLayers[0].active);