Bug 1630569 - Change the limit at which audio is muted with high or low playback rates, and make it and other parameters configurable via prefs. r=alwu

Differential Revision: https://phabricator.services.mozilla.com/D135066

dom/html/HTMLMediaElement.cpp

@@ -181,12 +181,6 @@ static const uint32_t STALL_MS = 3000;
 static const double MIN_PLAYBACKRATE = 1.0 / 16;
 // Maximum playbackRate for a media
 static const double MAX_PLAYBACKRATE = 16.0;
-// These are the limits beyonds which SoundTouch does not perform too well and
-// when speech is hard to understand anyway. Threshold above which audio is
-// muted
-static const double THRESHOLD_HIGH_PLAYBACKRATE_AUDIO = 4.0;
-// Threshold under which audio is muted
-static const double THRESHOLD_LOW_PLAYBACKRATE_AUDIO = 0.25;
 
 static double ClampPlaybackRate(double aPlaybackRate) {
   MOZ_ASSERT(aPlaybackRate >= 0.0);
@@ -6763,10 +6757,10 @@ void HTMLMediaElement::SetPlaybackRate(double aPlaybackRate, ErrorResult& aRv) {
   }
 
   mPlaybackRate = aPlaybackRate;
-
+  // Playback rate threshold above which audio is muted.
+  uint32_t threshold = StaticPrefs::media_audio_playbackrate_muting_threshold();
   if (mPlaybackRate != 0.0 &&
-      (mPlaybackRate > THRESHOLD_HIGH_PLAYBACKRATE_AUDIO ||
-       mPlaybackRate < THRESHOLD_LOW_PLAYBACKRATE_AUDIO)) {
+      (mPlaybackRate > threshold || mPlaybackRate < 1. / threshold)) {
     SetMutedInternal(mMuted | MUTED_BY_INVALID_PLAYBACK_RATE);
   } else {
     SetMutedInternal(mMuted & ~MUTED_BY_INVALID_PLAYBACK_RATE);

dom/media/AudioStream.cpp

@@ -28,6 +28,7 @@
 #include "Tracing.h"
 #include "webaudio/blink/DenormalDisabler.h"
 #include "AudioThreadRegistry.h"
+#include "mozilla/StaticPrefs_media.h"
 
 // Use abort() instead of exception in SoundTouch.
 #define ST_NO_EXCEPTION_HANDLING 1
@@ -178,9 +179,15 @@ nsresult AudioStream::EnsureTimeStretcherInitializedUnlocked() {
     // We are going to use a smaller 10ms sequence size to improve speech
     // clarity, giving more resolution at high tempo and less reverb at low
     // tempo. Maintain 15ms seekwindow and 8ms overlap for smoothness.
-    mTimeStretcher->setSetting(SETTING_SEQUENCE_MS, 10);
-    mTimeStretcher->setSetting(SETTING_SEEKWINDOW_MS, 15);
-    mTimeStretcher->setSetting(SETTING_OVERLAP_MS, 8);
+    mTimeStretcher->setSetting(
+        SETTING_SEQUENCE_MS,
+        StaticPrefs::media_audio_playbackrate_soundtouch_sequence_ms());
+    mTimeStretcher->setSetting(
+        SETTING_SEEKWINDOW_MS,
+        StaticPrefs::media_audio_playbackrate_soundtouch_seekwindow_ms());
+    mTimeStretcher->setSetting(
+        SETTING_OVERLAP_MS,
+        StaticPrefs::media_audio_playbackrate_soundtouch_overlap_ms());
   }
   return NS_OK;
 }

dom/media/mediasink/AudioDecoderInputTrack.cpp

@@ -6,6 +6,7 @@
 
 #include "MediaData.h"
 #include "mozilla/ScopeExit.h"
+#include "mozilla/StaticPrefs_media.h"
 #include "Tracing.h"
 
 // Use abort() instead of exception in SoundTouch.
@@ -638,9 +639,15 @@ void AudioDecoderInputTrack::EnsureTimeStretcher() {
     // We are going to use a smaller 10ms sequence size to improve speech
     // clarity, giving more resolution at high tempo and less reverb at low
     // tempo. Maintain 15ms seekwindow and 8ms overlap for smoothness.
-    mTimeStretcher->setSetting(SETTING_SEQUENCE_MS, 10);
-    mTimeStretcher->setSetting(SETTING_SEEKWINDOW_MS, 15);
-    mTimeStretcher->setSetting(SETTING_OVERLAP_MS, 8);
+    mTimeStretcher->setSetting(
+        SETTING_SEQUENCE_MS,
+        StaticPrefs::media_audio_playbackrate_soundtouch_sequence_ms());
+    mTimeStretcher->setSetting(
+        SETTING_SEEKWINDOW_MS,
+        StaticPrefs::media_audio_playbackrate_soundtouch_seekwindow_ms());
+    mTimeStretcher->setSetting(
+        SETTING_OVERLAP_MS,
+        StaticPrefs::media_audio_playbackrate_soundtouch_overlap_ms());
     SetTempoAndRateForTimeStretcher();
     LOG("Create TimeStretcher (channel=%d, playbackRate=%f, preservePitch=%d)",
         GetChannelCountForTimeStretcher(), mPlaybackRate, mPreservesPitch);

modules/libpref/init/StaticPrefList.yaml

@@ -9236,6 +9236,40 @@
   mirror: always
 #endif
 
+# When the playback rate of an HTMLMediaElement is greater than this value, or
+# lower than the inverse of this value, the audio is muted.
+- name: media.audio.playbackrate.muting_threshold
+  type: uint32_t
+  value: 8
+  mirror: always
+
+# Time-stretch algorithm single processing sequence length in milliseconds.
+# This determines to how long sequences the original sound is chopped in the
+# time-stretch algorithm.
+- name: media.audio.playbackrate.soundtouch_sequence_ms
+  type: RelaxedAtomicInt32
+  value: 10
+  mirror: always
+
+# Time-stretch algorithm seeking window length in milliseconds for algorithm
+# that finds the best possible overlapping location. This determines from how
+# wide window the algorithm may look for an optimal joining location when mixing
+# the sound sequences back together.
+- name: media.audio.playbackrate.soundtouch_seekwindow_ms
+  type: RelaxedAtomicInt32
+  value: 15
+  mirror: always
+
+# Time-stretch algorithm overlap length in milliseconds. When the chopped sound
+# sequences are mixed back together, to form a continuous sound stream, this
+# parameter defines over how long period the two consecutive sequences are let
+# to overlap each other.
+- name: media.audio.playbackrate.soundtouch_overlap_ms
+  type: RelaxedAtomicInt32
+  value: 8
+  mirror: always
+
+
 #---------------------------------------------------------------------------
 # Prefs starting with "midi."
 #---------------------------------------------------------------------------