Don't delay audio playback in non-kModeSyncPts

Bug: b/74612005
Test: On device unittests
Change-Id: I628a3ad8563fb1fb35ea783f73f24a62e497091a
Reviewed-on: https://chromium-review.googlesource.com/1028560Reviewed-by: Kenneth MacKay <kmackay@chromium.org>
Commit-Queue: Mina Almasry <almasrymina@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553677}

chromecast/media/cma/backend/buffering_mixer_source.cc

@@ -289,8 +289,7 @@ int BufferingMixerSource::FillAudioPlaybackFrames(
   // playback_start_timestamp_ accurate to +10ms. Improve this to be sample
   // accurate by writing a partial silence buffer when it's time to start
   // playback.
-  if (playback_absolute_timestamp != INT64_MIN &&
-      playback_absolute_timestamp < playback_start_timestamp_) {
+  if (playback_absolute_timestamp < playback_start_timestamp_) {
     return 0;
   }
 

chromecast/media/cma/backend/buffering_mixer_source.h

@@ -206,6 +206,8 @@ class BufferingMixerSource : public MixerInput::Source,
   const int max_queued_frames_;
   // Minimum number of frames buffered before starting to fill data.
   const int start_threshold_frames_;
+  // The absolute timestamp relative to clock monotonic (raw) at which the
+  // playback should start. INT64_MIN indicates playback should start ASAP.
   const int64_t playback_start_timestamp_;
 
   LockedMembers locked_members_;

chromecast/media/cma/backend/media_pipeline_backend_for_mixer.cc

@@ -70,13 +70,18 @@ bool MediaPipelineBackendForMixer::Initialize() {
 
 bool MediaPipelineBackendForMixer::Start(int64_t start_pts) {
   DCHECK_EQ(kStateInitialized, state_);
-  int64_t start_playback_timestamp_us =
-      MonotonicClockNow() + kSyncedPlaybackStartDelayUs;
+  int64_t start_playback_timestamp_us = INT64_MIN;
+  if (params_.sync_type == MediaPipelineDeviceParams::kModeSyncPts) {
+    start_playback_timestamp_us =
+        MonotonicClockNow() + kSyncedPlaybackStartDelayUs;
+  }
 
   if (audio_decoder_ && !audio_decoder_->Start(start_playback_timestamp_us))
     return false;
   if (video_decoder_ && !video_decoder_->Start(start_pts, true))
     return false;
+  // TODO(almasrymina): need to also start video playback at the proper time in
+  // non-kModeSyncPts.
   if (video_decoder_ &&
       !video_decoder_->SetPts(start_playback_timestamp_us, start_pts))
     return false;