Fixed time moving backwards in the AudioCodingModule.

webrtc/modules/audio_coding/acm2/audio_coding_module.cc

Index: webrtc/modules/audio_coding/acm2/audio_coding_module.cc
diff --git a/webrtc/modules/audio_coding/acm2/audio_coding_module.cc b/webrtc/modules/audio_coding/acm2/audio_coding_module.cc
index 6170d187bab14ab53b62fe9795c6c56332040c0a..b394c591567926b151b00a62c861f7f7bc35bbd1 100644
--- a/webrtc/modules/audio_coding/acm2/audio_coding_module.cc
+++ b/webrtc/modules/audio_coding/acm2/audio_coding_module.cc
@@ -472,6 +472,11 @@ int32_t AudioCodingModuleImpl::Encode(const InputData& input_data) {
   if (!HaveValidEncoder("Process"))
     return -1;
 
+  if(!first_frame_) {
+    RTC_DCHECK_GT(input_data.input_timestamp, last_timestamp_)
+        << "Time should not move backwards";
+  }
+
   // Scale the timestamp to the codec's RTP timestamp rate.
   uint32_t rtp_timestamp =
       first_frame_ ? input_data.input_timestamp
@@ -752,7 +757,8 @@ int AudioCodingModuleImpl::PreprocessToAddData(const AudioFrame& in_frame,
     expected_codec_ts_ = in_frame.timestamp_;
     first_10ms_data_ = true;
   } else if (in_frame.timestamp_ != expected_in_ts_) {
-    // TODO(turajs): Do we need a warning here.
+    LOG(LS_WARNING) << "Unexpected input timestamp: " << in_frame.timestamp_
+                    << ", expected: " << expected_in_ts_;
     expected_codec_ts_ +=
         (in_frame.timestamp_ - expected_in_ts_) *
         static_cast<uint32_t>(
@@ -764,9 +770,19 @@ int AudioCodingModuleImpl::PreprocessToAddData(const AudioFrame& in_frame,
 
   if (!down_mix && !resample) {
     // No pre-processing is required.
+    if (expected_in_ts_ == expected_codec_ts_) {
+      // If we've never resampled, we can use the input frame as-is
+      *ptr_out = &in_frame;
+    } else {
+      // Otherwise we'll need to alter the timestamp. Since in_frame is const,
+      // we'll have to make a copy of it.
+      preprocess_frame_.CopyFrom(in_frame);
+      preprocess_frame_.timestamp_ = expected_codec_ts_;
+      *ptr_out = &preprocess_frame_;
+    }
+
     expected_in_ts_ += static_cast<uint32_t>(in_frame.samples_per_channel_);
     expected_codec_ts_ += static_cast<uint32_t>(in_frame.samples_per_channel_);
-    *ptr_out = &in_frame;
     return 0;
   }