NetEq::GetPlayoutTimestamp returns empty during CNG

webrtc/modules/audio_coding/neteq/neteq_impl.cc

Index: webrtc/modules/audio_coding/neteq/neteq_impl.cc
diff --git a/webrtc/modules/audio_coding/neteq/neteq_impl.cc b/webrtc/modules/audio_coding/neteq/neteq_impl.cc
index 40a031421eb96e2bcfed865408ca2c7b8dea9555..db37e716d66dde966a4cac42f10dd47166c4f42c 100644
--- a/webrtc/modules/audio_coding/neteq/neteq_impl.cc
+++ b/webrtc/modules/audio_coding/neteq/neteq_impl.cc
@@ -403,9 +403,11 @@ void NetEqImpl::DisableVad() {
 
 rtc::Optional<uint32_t> NetEqImpl::GetPlayoutTimestamp() const {
   rtc::CritScope lock(&crit_sect_);
-  if (first_packet_) {
+  if (first_packet_ || last_mode_ == kModeRfc3389Cng ||
+      last_mode_ == kModeCodecInternalCng) {
     // We don't have a valid RTP timestamp until we have decoded our first
-    // RTP packet.
+    // RTP packet. Also, the RTP timestamp is not accurate while playing CNG,
+    // which is indicated by returning an empty value.
     return rtc::Optional<uint32_t>();
   }
   return rtc::Optional<uint32_t>(