diff --git a/video/end_to_end_tests/multi_codec_receive_tests.cc b/video/end_to_end_tests/multi_codec_receive_tests.cc
index 44dad576c0..c12b3933ea 100644
--- a/video/end_to_end_tests/multi_codec_receive_tests.cc
+++ b/video/end_to_end_tests/multi_codec_receive_tests.cc
@@ -115,7 +115,7 @@ class FrameObserver : public test::RtpRtcpObserver,
   }
 
   rtc::CriticalSection crit_;
-  absl::optional<uint32_t> last_timestamp_;
+  absl::optional<uint32_t> last_timestamp_;  // Only accessed from pacer thread.
   absl::optional<uint8_t> expected_payload_type_ RTC_GUARDED_BY(crit_);
   int num_sent_frames_ RTC_GUARDED_BY(crit_) = 0;
   int num_rendered_frames_ RTC_GUARDED_BY(crit_) = 0;
@@ -212,6 +212,7 @@ void MultiCodecReceiveTest::RunTestWithCodecs(
     ConfigureEncoder(configs[0]);
     CreateMatchingReceiveConfigs(receive_transport_.get());
     video_receive_configs_[0].renderer = &observer_;
+    // Disable to avoid post-decode frame dropping in VideoRenderFrames.
     video_receive_configs_[0].enable_prerenderer_smoothing = false;
     ConfigureDecoders(configs);
     CreateVideoStreams();