Don't always downsample to 16kHz in the reverse stream in APM

webrtc/modules/audio_processing/audio_processing_impl.cc

Index: webrtc/modules/audio_processing/audio_processing_impl.cc
diff --git a/webrtc/modules/audio_processing/audio_processing_impl.cc b/webrtc/modules/audio_processing/audio_processing_impl.cc
index 3a83d1c2d69f65d8cede7f12e2f3eb2fa11a4b63..af6d9b7a2123bc0daa289ed769b99107be8d181f 100644
--- a/webrtc/modules/audio_processing/audio_processing_impl.cc
+++ b/webrtc/modules/audio_processing/audio_processing_impl.cc
@@ -366,18 +366,20 @@ int AudioProcessingImpl::InitializeLocked(const ProcessingConfig& config) {
       std::min(formats_.api_format.input_stream().sample_rate_hz(),
                formats_.api_format.output_stream().sample_rate_hz())));
 
-  // We normally process the reverse stream at 16 kHz. Unless...
-  int rev_proc_rate = kSampleRate16kHz;
+  int rev_proc_rate = ClosestHigherNativeRate(std::min(
+      formats_.api_format.reverse_input_stream().sample_rate_hz(),
+      formats_.api_format.reverse_output_stream().sample_rate_hz()));
+  // TODO(aluebs): Remove this restriction once we figure out why the 3-band
+  // splitting filter degrades the AEC performance.
+  if (rev_proc_rate > kSampleRate32kHz) {
+    rev_proc_rate = is_rev_processed() ? kSampleRate32kHz : kSampleRate16kHz;
+  }
+  // If the forward sample rate is 8 kHz, the reverse stream is also processed
+  // at this rate.
   if (capture_nonlocked_.fwd_proc_format.sample_rate_hz() == kSampleRate8kHz) {
-    // ...the forward stream is at 8 kHz.
     rev_proc_rate = kSampleRate8kHz;
   } else {
-    if (formats_.api_format.reverse_input_stream().sample_rate_hz() ==
-        kSampleRate32kHz) {
-      // ...or the input is at 32 kHz, in which case we use the splitting
-      // filter rather than the resampler.
-      rev_proc_rate = kSampleRate32kHz;
-    }
+    rev_proc_rate = std::max(rev_proc_rate, static_cast<int>(kSampleRate16kHz));
   }
 
   // Always downmix the reverse stream to mono for analysis. This has been
@@ -1151,11 +1153,11 @@ bool AudioProcessingImpl::is_rev_processed() const {
 
 bool AudioProcessingImpl::rev_synthesis_needed() const {
   return (is_rev_processed() &&
-          formats_.rev_proc_format.sample_rate_hz() == kSampleRate32kHz);
+          is_multi_band(formats_.rev_proc_format.sample_rate_hz()));
 }
 
 bool AudioProcessingImpl::rev_analysis_needed() const {
-  return formats_.rev_proc_format.sample_rate_hz() == kSampleRate32kHz &&
+  return is_multi_band(formats_.rev_proc_format.sample_rate_hz()) &&
          (is_rev_processed() ||
           public_submodules_->echo_cancellation
               ->is_enabled_render_side_query() ||