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

[ossu, 2016/07/06 08:38:56]

Here is where the output timestamp gets adjusted if there's a mismatch between a
codec's sample rate and its RTP clockrate.

@@ -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.

[ossu, 2016/07/05 16:39:04]

Probably.

+    LOG(LS_WARNING) << "Unexpected input timestamp: " << in_frame.timestamp_
+                    << ", expected: " << expected_in_ts_;

[tlegrand-webrtc, 2016/07/06 08:25:44]

Will we only end up here once in the case the codec changes?

[ossu, 2016/07/06 08:38:56]

This shouldn't happen when the codec changes. In fact, I don't think we should
ever end up here. However, seeing as it's something we're not expecting, I think
we should log it. It could help track down other issues when we don't have
access to much other than logs.

Now, if this happens, we adjust for it and it should only log once, yes. Unless
something very strange is happening at the input (like maybe timestamps not
moving forward at all).

     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;
   }