allow empty scalability mode in AV1 encoder

Bug: chromium:1170699
Change-Id: I74c633e74c85c3b940d6302cdc8fa319e187b1e5
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/204221
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33122}
diff --git a/modules/video_coding/codecs/av1/libaom_av1_encoder.cc b/modules/video_coding/codecs/av1/libaom_av1_encoder.cc
index 2d24450..bf73dec 100644
--- a/modules/video_coding/codecs/av1/libaom_av1_encoder.cc
+++ b/modules/video_coding/codecs/av1/libaom_av1_encoder.cc
@@ -169,8 +169,8 @@
   }
   absl::string_view scalability_mode = encoder_settings_.ScalabilityMode();
   if (scalability_mode.empty()) {
-    RTC_LOG(LS_WARNING) << "Scalability mode is not set.";
-    return WEBRTC_VIDEO_CODEC_ERROR;
+    RTC_LOG(LS_WARNING) << "Scalability mode is not set, using 'NONE'.";
+    scalability_mode = "NONE";
   }
   svc_controller_ = CreateScalabilityStructure(scalability_mode);
   if (svc_controller_ == nullptr) {
diff --git a/modules/video_coding/codecs/av1/libaom_av1_encoder_unittest.cc b/modules/video_coding/codecs/av1/libaom_av1_encoder_unittest.cc
index cd86f5a..5555485 100644
--- a/modules/video_coding/codecs/av1/libaom_av1_encoder_unittest.cc
+++ b/modules/video_coding/codecs/av1/libaom_av1_encoder_unittest.cc
@@ -54,7 +54,6 @@
   std::unique_ptr<VideoEncoder> encoder = CreateLibaomAv1Encoder();
   ASSERT_TRUE(encoder);
   VideoCodec codec_settings = DefaultCodecSettings();
-  codec_settings.SetScalabilityMode("NONE");
   EXPECT_EQ(encoder->InitEncode(&codec_settings, DefaultEncoderSettings()),
             WEBRTC_VIDEO_CODEC_OK);
   EXPECT_EQ(encoder->Release(), WEBRTC_VIDEO_CODEC_OK);