76 lines
2.5 KiB
C++
76 lines
2.5 KiB
C++
// Copyright (c) 2012 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "media/base/audio_timestamp_helper.h"
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#include "base/logging.h"
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#include "media/base/buffers.h"
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namespace media {
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AudioTimestampHelper::AudioTimestampHelper(int samples_per_second)
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: base_timestamp_(kNoTimestamp()),
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frame_count_(0) {
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DCHECK_GT(samples_per_second, 0);
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double fps = samples_per_second;
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microseconds_per_frame_ = base::Time::kMicrosecondsPerSecond / fps;
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}
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void AudioTimestampHelper::SetBaseTimestamp(base::TimeDelta base_timestamp) {
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base_timestamp_ = base_timestamp;
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frame_count_ = 0;
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}
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base::TimeDelta AudioTimestampHelper::base_timestamp() const {
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return base_timestamp_;
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}
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void AudioTimestampHelper::AddFrames(int frame_count) {
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DCHECK_GE(frame_count, 0);
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DCHECK(base_timestamp_ != kNoTimestamp());
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frame_count_ += frame_count;
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}
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base::TimeDelta AudioTimestampHelper::GetTimestamp() const {
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return ComputeTimestamp(frame_count_);
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}
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base::TimeDelta AudioTimestampHelper::GetFrameDuration(int frame_count) const {
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DCHECK_GE(frame_count, 0);
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base::TimeDelta end_timestamp = ComputeTimestamp(frame_count_ + frame_count);
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return end_timestamp - GetTimestamp();
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}
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int64 AudioTimestampHelper::GetFramesToTarget(base::TimeDelta target) const {
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DCHECK(base_timestamp_ != kNoTimestamp());
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DCHECK(target >= base_timestamp_);
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int64 delta_in_us = (target - GetTimestamp()).InMicroseconds();
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if (delta_in_us == 0)
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return 0;
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// Compute a timestamp relative to |base_timestamp_| since timestamps
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// created from |frame_count_| are computed relative to this base.
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// This ensures that the time to frame computation here is the proper inverse
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// of the frame to time computation in ComputeTimestamp().
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base::TimeDelta delta_from_base = target - base_timestamp_;
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// Compute frame count for the time delta. This computation rounds to
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// the nearest whole number of frames.
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double threshold = microseconds_per_frame_ / 2;
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int64 target_frame_count =
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(delta_from_base.InMicroseconds() + threshold) / microseconds_per_frame_;
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return target_frame_count - frame_count_;
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}
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base::TimeDelta AudioTimestampHelper::ComputeTimestamp(
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int64 frame_count) const {
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DCHECK_GE(frame_count, 0);
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DCHECK(base_timestamp_ != kNoTimestamp());
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double frames_us = microseconds_per_frame_ * frame_count;
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return base_timestamp_ + base::TimeDelta::FromMicroseconds(frames_us);
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}
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} // namespace media
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