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// Copyright (c) 2009 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/base/synchronizer.h"
namespace media {
const int64 Synchronizer::kMinFrameDelayUs = 0;
const int64 Synchronizer::kMaxFrameDelayUs = 250000;
Synchronizer::Synchronizer() {
}
Synchronizer::~Synchronizer() {
}
void Synchronizer::StartRendering() {
rendering_start_ = base::TimeTicks::Now();
}
void Synchronizer::StopRendering() {
rendering_stop_ = base::TimeTicks::Now();
}
void Synchronizer::CalculateDelay(base::TimeDelta time,
const StreamSample* now,
const StreamSample* next,
base::TimeDelta* delay_out,
bool* should_skip_out) {
// How long rendering took.
base::TimeDelta render_delta = rendering_stop_ - rendering_start_;
// The duration to display the sample |now|.
base::TimeDelta duration = now->GetDuration();
// The presentation timestamp (pts) of the sample |now|.
base::TimeDelta now_pts = now->GetTimestamp();
// The presentation timestamp (pts) of the next sample.
base::TimeDelta next_pts;
// If we were provided the next sample in the stream |next|, use it to
// calculate the actual sample duration as opposed to the expected duration
// provided by the current sample |now|.
//
// We also use |next| to get the exact next timestamp as opposed to assuming
// it will be |now| + |now|'s duration, which may not always be true.
if (next) {
next_pts = next->GetTimestamp();
duration = next_pts - now_pts;
// Timestamps appear out of order, so skip this frame.
if (duration.InMicroseconds() < 0) {
*delay_out = base::TimeDelta();
*should_skip_out = true;
return;
}
} else {
// Assume next presentation timestamp is |now| + |now|'s duration.
next_pts = now_pts + duration;
}
base::TimeDelta sleep;
if (time == last_time_) {
// The audio time has not changed. To avoid sudden bursts of video after
// we get audio timing information, we try and guess the current time
// using the duration of the frame.
sleep = duration - render_delta;
if (sleep.InMicroseconds() < kMinFrameDelayUs) {
sleep = base::TimeDelta::FromMicroseconds(kMinFrameDelayUs);
}
} else {
// The audio time has changed. The amount of time to delay is equal to
// the time until the next sample from now minus how long it takes to
// render, clamped to within the min/max frame delay constants.
sleep = next_pts - time - render_delta;
if (sleep.InMicroseconds() < kMinFrameDelayUs) {
sleep = base::TimeDelta::FromMicroseconds(kMinFrameDelayUs);
} else if (sleep.InMicroseconds() > kMaxFrameDelayUs) {
sleep = base::TimeDelta::FromMicroseconds(kMaxFrameDelayUs);
}
}
last_time_ = time;
*delay_out = sleep;
*should_skip_out = false;
}
} // namespace media
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