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/*
* Copyright (c) 2022 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef VIDEO_DECODE_SYNCHRONIZER_H_
#define VIDEO_DECODE_SYNCHRONIZER_H_
#include <stdint.h>
#include <functional>
#include <memory>
#include <set>
#include <utility>
#include "absl/types/optional.h"
#include "api/metronome/metronome.h"
#include "api/sequence_checker.h"
#include "api/task_queue/task_queue_base.h"
#include "api/units/timestamp.h"
#include "rtc_base/checks.h"
#include "rtc_base/thread_annotations.h"
#include "video/frame_decode_scheduler.h"
#include "video/frame_decode_timing.h"
namespace webrtc {
// DecodeSynchronizer synchronizes the frame scheduling by coalescing decoding
// on the metronome.
//
// A video receive stream can use the DecodeSynchronizer by receiving a
// FrameDecodeScheduler instance with `CreateSynchronizedFrameScheduler()`.
// This instance implements FrameDecodeScheduler and can be used as a normal
// scheduler. This instance is owned by the receive stream, and is borrowed by
// the DecodeSynchronizer. The DecodeSynchronizer will stop borrowing the
// instance when `FrameDecodeScheduler::Stop()` is called, after which the
// scheduler may be destroyed by the receive stream.
//
// When a frame is scheduled for decode by a receive stream using the
// DecodeSynchronizer, it will instead be executed on the metronome during the
// tick interval where `max_decode_time` occurs. For example, if a frame is
// scheduled for decode in 50ms and the tick interval is 20ms, then the frame
// will be released for decoding in 2 ticks. See below for illustration,
//
// In the case where the decode time is in the past, or must occur before the
// next metronome tick then the frame will be released right away, allowing a
// delayed stream to catch up quickly.
//
// DecodeSynchronizer is single threaded - all method calls must run on the
// `worker_queue_`.
class DecodeSynchronizer {
public:
DecodeSynchronizer(Clock* clock,
Metronome* metronome,
TaskQueueBase* worker_queue);
~DecodeSynchronizer();
DecodeSynchronizer(const DecodeSynchronizer&) = delete;
DecodeSynchronizer& operator=(const DecodeSynchronizer&) = delete;
std::unique_ptr<FrameDecodeScheduler> CreateSynchronizedFrameScheduler();
private:
class ScheduledFrame {
public:
ScheduledFrame(uint32_t rtp_timestamp,
FrameDecodeTiming::FrameSchedule schedule,
FrameDecodeScheduler::FrameReleaseCallback callback);
// Disallow copy since `callback` should only be moved.
ScheduledFrame(const ScheduledFrame&) = delete;
ScheduledFrame& operator=(const ScheduledFrame&) = delete;
ScheduledFrame(ScheduledFrame&&) = default;
ScheduledFrame& operator=(ScheduledFrame&&) = default;
// Executes `callback_`.
void RunFrameReleaseCallback() &&;
uint32_t rtp_timestamp() const { return rtp_timestamp_; }
Timestamp LatestDecodeTime() const;
private:
uint32_t rtp_timestamp_;
FrameDecodeTiming::FrameSchedule schedule_;
FrameDecodeScheduler::FrameReleaseCallback callback_;
};
class SynchronizedFrameDecodeScheduler : public FrameDecodeScheduler {
public:
explicit SynchronizedFrameDecodeScheduler(DecodeSynchronizer* sync);
~SynchronizedFrameDecodeScheduler() override;
// Releases the outstanding frame for decoding. This invalidates
// `next_frame_`. There must be a frame scheduled.
ScheduledFrame ReleaseNextFrame();
// Returns `next_frame_.schedule.max_decode_time`. There must be a frame
// scheduled when this is called.
Timestamp LatestDecodeTime();
// FrameDecodeScheduler implementation.
absl::optional<uint32_t> ScheduledRtpTimestamp() override;
void ScheduleFrame(uint32_t rtp,
FrameDecodeTiming::FrameSchedule schedule,
FrameReleaseCallback cb) override;
void CancelOutstanding() override;
void Stop() override;
private:
DecodeSynchronizer* sync_;
absl::optional<ScheduledFrame> next_frame_;
bool stopped_ = false;
};
void OnFrameScheduled(SynchronizedFrameDecodeScheduler* scheduler);
void RemoveFrameScheduler(SynchronizedFrameDecodeScheduler* scheduler);
void ScheduleNextTick();
void OnTick();
Clock* const clock_;
TaskQueueBase* const worker_queue_;
Metronome* const metronome_;
Timestamp expected_next_tick_ = Timestamp::PlusInfinity();
std::set<SynchronizedFrameDecodeScheduler*> schedulers_
RTC_GUARDED_BY(worker_queue_);
bool tick_scheduled_ = false;
ScopedTaskSafetyDetached safety_;
};
} // namespace webrtc
#endif // VIDEO_DECODE_SYNCHRONIZER_H_
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