[VP9 SVC] Round spatial layers dimensions to ensure integer scaling factors are used

Bug: webrtc:11652
Change-Id: Id3642d607f62b72a567d521d9874b8588c2ce429
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/176517
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31465}

modules/video_coding/codecs/vp9/svc_config.cc

@@ -79,6 +79,11 @@ std::vector<SpatialLayer> ConfigureSvcNormalVideo(size_t input_width,
   // First active layer must be configured.
   num_spatial_layers = std::max(num_spatial_layers, first_active_layer + 1);
 
+  // Ensure top layer is even enough.
+  int required_divisiblity = 1 << num_spatial_layers;
+  input_width = input_width - input_width % required_divisiblity;
+  input_height = input_height - input_height % required_divisiblity;
+
   for (size_t sl_idx = first_active_layer; sl_idx < num_spatial_layers;
        ++sl_idx) {
     SpatialLayer spatial_layer = {0};

modules/video_coding/video_codec_initializer.cc

@@ -219,6 +219,14 @@ VideoCodec VideoCodecInitializer::VideoEncoderConfigToVideoCodec(
         video_codec.spatialLayers[i] = spatial_layers[i];
       }
 
+      // The top spatial layer dimensions may not be equal to the input
+      // resolution because of the rounding or explicit configuration.
+      // This difference must be propagated to the stream configuration.
+      video_codec.width = spatial_layers.back().width;
+      video_codec.height = spatial_layers.back().height;
+      video_codec.simulcastStream[0].width = spatial_layers.back().width;
+      video_codec.simulcastStream[0].height = spatial_layers.back().height;
+
       // Update layering settings.
       video_codec.VP9()->numberOfSpatialLayers =
           static_cast<unsigned char>(spatial_layers.size());