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 AudioTimestampHelper(int samples_per_second)12AudioTimestampHelper::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 SetBaseTimestamp(base::TimeDelta base_timestamp)20void AudioTimestampHelper::SetBaseTimestamp(base::TimeDelta base_timestamp) { 21 base_timestamp_ = base_timestamp; 22 frame_count_ = 0; 23 } 24 base_timestamp() const25base::TimeDelta AudioTimestampHelper::base_timestamp() const { 26 return base_timestamp_; 27 } 28 AddFrames(int frame_count)29void AudioTimestampHelper::AddFrames(int frame_count) { 30 DCHECK_GE(frame_count, 0); 31 DCHECK(base_timestamp_ != kNoTimestamp()); 32 frame_count_ += frame_count; 33 } 34 GetTimestamp() const35base::TimeDelta AudioTimestampHelper::GetTimestamp() const { 36 return ComputeTimestamp(frame_count_); 37 } 38 GetFrameDuration(int frame_count) const39base::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 GetFramesToTarget(base::TimeDelta target) const45int64 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 ComputeTimestamp(int64 frame_count) const67base::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