Use double microseconds for tracking back/front timestamp in AudioClock.

media/filters/audio_clock.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/filters/audio_clock.h"
 
 #include <stdint.h>
 #include <stddef.h>
 
 #include <algorithm>
+#include <cmath>
 
 #include "base/logging.h"
 
 namespace media {
 
 AudioClock::AudioClock(base::TimeDelta start_timestamp, int sample_rate)
     : start_timestamp_(start_timestamp),
       microseconds_per_frame_(
           static_cast<double>(base::Time::kMicrosecondsPerSecond) /
           sample_rate),
       total_buffered_frames_(0),
-      front_timestamp_(start_timestamp),
-      back_timestamp_(start_timestamp) {
-}
+      front_timestamp_micros_(start_timestamp.InMicroseconds()),
+      back_timestamp_micros_(start_timestamp.InMicroseconds()) {}
 
 AudioClock::~AudioClock() {
 }
 
 void AudioClock::WroteAudio(int frames_written,
                             int frames_requested,
                             int delay_frames,
                             double playback_rate) {
   DCHECK_GE(frames_written, 0);
   DCHECK_LE(frames_written, frames_requested);
   DCHECK_GE(delay_frames, 0);
   DCHECK_GE(playback_rate, 0);
 
   // First write: initialize buffer with silence.
-  if (start_timestamp_ == front_timestamp_ && buffered_.empty())
+  if (start_timestamp_.InMicroseconds() == front_timestamp_micros_ &&
+      buffered_.empty()) {
     PushBufferedAudioData(delay_frames, 0.0);
+  }
 
   // Move frames from |buffered_| into the computed timestamp based on
   // |delay_frames|.
   //
   // The ordering of compute -> push -> pop eliminates unnecessary memory
   // reallocations in cases where |buffered_| gets emptied.
   int64_t frames_played =
       std::max(INT64_C(0), total_buffered_frames_ - delay_frames);
   PushBufferedAudioData(frames_written, playback_rate);
   PushBufferedAudioData(frames_requested - frames_written, 0.0);
   PopBufferedAudioData(frames_played);
 
   // Update our front and back timestamps.  The back timestamp is considered the
   // authoritative source of truth, so base the front timestamp on range of data
   // buffered.  Doing so avoids accumulation errors on the front timestamp.
-  back_timestamp_ += base::TimeDelta::FromMicroseconds(
-      frames_written * playback_rate * microseconds_per_frame_);
+  back_timestamp_micros_ +=
+      frames_written * playback_rate * microseconds_per_frame_;
+
   // Don't let front timestamp move earlier in time, as could occur due to delay
   // frames pushed in the first write, above.
-  front_timestamp_ = std::max(front_timestamp_,
-                              back_timestamp_ - ComputeBufferedMediaDuration());
-  DCHECK_GE(front_timestamp_, start_timestamp_);
-  DCHECK_LE(front_timestamp_, back_timestamp_);
+  front_timestamp_micros_ =
+      std::max(front_timestamp_micros_,
+               back_timestamp_micros_ - ComputeBufferedMediaDurationMicros());
+  DCHECK_GE(front_timestamp_micros_, start_timestamp_.InMicroseconds());
+  DCHECK_LE(front_timestamp_micros_, back_timestamp_micros_);
 }
 
 void AudioClock::CompensateForSuspendedWrites(base::TimeDelta elapsed,
                                               int delay_frames) {
   const int64_t frames_elapsed =
       elapsed.InMicroseconds() / microseconds_per_frame_ + 0.5;
 
   // No need to do anything if we're within the limits of our played out audio
   // or there are no delay frames, the next WroteAudio() call will expire
   // everything correctly.
   if (frames_elapsed < total_buffered_frames_ || !delay_frames)
     return;
 
   // Otherwise, flush everything and prime with the delay frames.
   WroteAudio(0, 0, 0, 0);
   DCHECK(buffered_.empty());
   PushBufferedAudioData(delay_frames, 0.0);
 }
 
 base::TimeDelta AudioClock::TimeUntilPlayback(base::TimeDelta timestamp) const {
-  DCHECK_GE(timestamp, front_timestamp_);
-  DCHECK_LE(timestamp, back_timestamp_);
+  // Use front/back_timestamp() methods rather than internal members. The public
+  // methods round to the nearest microsecond for conversion to TimeDelta and
+  // the rounded value will likely be used by the caller.
+  DCHECK_GE(timestamp, front_timestamp());
+  DCHECK_LE(timestamp, back_timestamp());
 
   int64_t frames_until_timestamp = 0;
   double timestamp_us = timestamp.InMicroseconds();
-  double media_time_us = front_timestamp_.InMicroseconds();
+  double media_time_us = front_timestamp().InMicroseconds();
 
   for (size_t i = 0; i < buffered_.size(); ++i) {
     // Leading silence is always accounted prior to anything else.
     if (buffered_[i].playback_rate == 0) {
       frames_until_timestamp += buffered_[i].frames;
       continue;
     }
 
     // Calculate upper bound on media time for current block of buffered frames.
     double delta_us = buffered_[i].frames * buffered_[i].playback_rate *
                       microseconds_per_frame_;
     double max_media_time_us = media_time_us + delta_us;
 
     // Determine amount of media time to convert to frames for current block. If
     // target timestamp falls within current block, scale the amount of frames
     // based on remaining amount of media time.
     if (timestamp_us <= max_media_time_us) {
       frames_until_timestamp +=
           buffered_[i].frames * (timestamp_us - media_time_us) / delta_us;
       break;
     }
 
     media_time_us = max_media_time_us;
     frames_until_timestamp += buffered_[i].frames;
   }
 
-  return base::TimeDelta::FromMicroseconds(frames_until_timestamp *
-                                           microseconds_per_frame_);
+  return base::TimeDelta::FromMicroseconds(
+      std::round(frames_until_timestamp * microseconds_per_frame_));
 }
 
 void AudioClock::ContiguousAudioDataBufferedForTesting(
     base::TimeDelta* total,
     base::TimeDelta* same_rate_total) const {
   double scaled_frames = 0;
   double scaled_frames_at_same_rate = 0;
   bool found_silence = false;
   for (size_t i = 0; i < buffered_.size(); ++i) {
     if (buffered_[i].playback_rate == 0) {
@@ skipping 44 matching lines @@
   while (frames > 0) {
     int64_t frames_to_pop = std::min(buffered_.front().frames, frames);
     buffered_.front().frames -= frames_to_pop;
     if (buffered_.front().frames == 0)
       buffered_.pop_front();
 
     frames -= frames_to_pop;
   }
 }
 
-base::TimeDelta AudioClock::ComputeBufferedMediaDuration() const {
+double AudioClock::ComputeBufferedMediaDurationMicros() const {
   double scaled_frames = 0;
   for (const auto& buffer : buffered_)
     scaled_frames += buffer.frames * buffer.playback_rate;
-  return base::TimeDelta::FromMicroseconds(scaled_frames *
-                                           microseconds_per_frame_);
+  return scaled_frames * microseconds_per_frame_;
 }
 
 }  // namespace media