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      1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include "media/base/audio_timestamp_helper.h"
      6 
      7 #include "base/logging.h"
      8 #include "media/base/buffers.h"
      9 
     10 namespace media {
     11 
     12 AudioTimestampHelper::AudioTimestampHelper(int samples_per_second)
     13     : base_timestamp_(kNoTimestamp()),
     14       frame_count_(0) {
     15   DCHECK_GT(samples_per_second, 0);
     16   double fps = samples_per_second;
     17   microseconds_per_frame_ = base::Time::kMicrosecondsPerSecond / fps;
     18 }
     19 
     20 void AudioTimestampHelper::SetBaseTimestamp(base::TimeDelta base_timestamp) {
     21   base_timestamp_ = base_timestamp;
     22   frame_count_ = 0;
     23 }
     24 
     25 base::TimeDelta AudioTimestampHelper::base_timestamp() const {
     26   return base_timestamp_;
     27 }
     28 
     29 void AudioTimestampHelper::AddFrames(int frame_count) {
     30   DCHECK_GE(frame_count, 0);
     31   DCHECK(base_timestamp_ != kNoTimestamp());
     32   frame_count_ += frame_count;
     33 }
     34 
     35 base::TimeDelta AudioTimestampHelper::GetTimestamp() const {
     36   return ComputeTimestamp(frame_count_);
     37 }
     38 
     39 base::TimeDelta AudioTimestampHelper::GetFrameDuration(int frame_count) const {
     40   DCHECK_GE(frame_count, 0);
     41   base::TimeDelta end_timestamp = ComputeTimestamp(frame_count_ + frame_count);
     42   return end_timestamp - GetTimestamp();
     43 }
     44 
     45 int64 AudioTimestampHelper::GetFramesToTarget(base::TimeDelta target) const {
     46   DCHECK(base_timestamp_ != kNoTimestamp());
     47   DCHECK(target >= base_timestamp_);
     48 
     49   int64 delta_in_us = (target - GetTimestamp()).InMicroseconds();
     50   if (delta_in_us == 0)
     51     return 0;
     52 
     53   // Compute a timestamp relative to |base_timestamp_| since timestamps
     54   // created from |frame_count_| are computed relative to this base.
     55   // This ensures that the time to frame computation here is the proper inverse
     56   // of the frame to time computation in ComputeTimestamp().
     57   base::TimeDelta delta_from_base = target - base_timestamp_;
     58 
     59   // Compute frame count for the time delta. This computation rounds to
     60   // the nearest whole number of frames.
     61   double threshold = microseconds_per_frame_ / 2;
     62   int64 target_frame_count =
     63       (delta_from_base.InMicroseconds() + threshold) / microseconds_per_frame_;
     64   return target_frame_count - frame_count_;
     65 }
     66 
     67 base::TimeDelta AudioTimestampHelper::ComputeTimestamp(
     68     int64 frame_count) const {
     69   DCHECK_GE(frame_count, 0);
     70   DCHECK(base_timestamp_ != kNoTimestamp());
     71   double frames_us = microseconds_per_frame_ * frame_count;
     72   return base_timestamp_ + base::TimeDelta::FromMicroseconds(frames_us);
     73 }
     74 
     75 }  // namespace media
     76