modules/video_coding/timing.cc

/*
 *  Copyright (c) 2011 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.
 */

#include "modules/video_coding/timing.h"


#include <algorithm>

#include "rtc_base/experiments/field_trial_parser.h"
#include "rtc_base/time/timestamp_extrapolator.h"
#include "system_wrappers/include/clock.h"
#include "system_wrappers/include/field_trial.h"

namespace webrtc {
namespace {
// Default pacing that is used for the low-latency renderer path.
constexpr TimeDelta kZeroPlayoutDelayDefaultMinPacing = TimeDelta::Millis(8);
}  // namespace

VCMTiming::VCMTiming(Clock* clock)
    : clock_(clock),
      ts_extrapolator_(std::make_unique<TimestampExtrapolator>(
          clock_->TimeInMilliseconds())),
      codec_timer_(std::make_unique<VCMCodecTimer>()),
      render_delay_ms_(kDefaultRenderDelayMs),
      min_playout_delay_ms_(0),
      max_playout_delay_ms_(10000),
      jitter_delay_ms_(0),
      current_delay_ms_(0),
      prev_frame_timestamp_(0),
      timing_frame_info_(),
      num_decoded_frames_(0),
      low_latency_renderer_enabled_("enabled", true),
      zero_playout_delay_min_pacing_("min_pacing",
                                     kZeroPlayoutDelayDefaultMinPacing),
      last_decode_scheduled_ts_(0) {
  ParseFieldTrial({&low_latency_renderer_enabled_},
                  field_trial::FindFullName("WebRTC-LowLatencyRenderer"));
  ParseFieldTrial({&zero_playout_delay_min_pacing_},
                  field_trial::FindFullName("WebRTC-ZeroPlayoutDelay"));
}

void VCMTiming::Reset() {
  MutexLock lock(&mutex_);
  ts_extrapolator_->Reset(clock_->TimeInMilliseconds());
  codec_timer_ = std::make_unique<VCMCodecTimer>();
  render_delay_ms_ = kDefaultRenderDelayMs;
  min_playout_delay_ms_ = 0;
  jitter_delay_ms_ = 0;
  current_delay_ms_ = 0;
  prev_frame_timestamp_ = 0;
}

void VCMTiming::set_render_delay(int render_delay_ms) {
  MutexLock lock(&mutex_);
  render_delay_ms_ = render_delay_ms;
}

void VCMTiming::set_min_playout_delay(int min_playout_delay_ms) {
  MutexLock lock(&mutex_);
  min_playout_delay_ms_ = min_playout_delay_ms;
}

int VCMTiming::min_playout_delay() {
  MutexLock lock(&mutex_);
  return min_playout_delay_ms_;
}

void VCMTiming::set_max_playout_delay(int max_playout_delay_ms) {
  MutexLock lock(&mutex_);
  max_playout_delay_ms_ = max_playout_delay_ms;
}

int VCMTiming::max_playout_delay() {
  MutexLock lock(&mutex_);
  return max_playout_delay_ms_;
}

void VCMTiming::SetJitterDelay(int jitter_delay_ms) {
  MutexLock lock(&mutex_);
  if (jitter_delay_ms != jitter_delay_ms_) {
    jitter_delay_ms_ = jitter_delay_ms;
    // When in initial state, set current delay to minimum delay.
    if (current_delay_ms_ == 0) {
      current_delay_ms_ = jitter_delay_ms_;
    }
  }
}

void VCMTiming::UpdateCurrentDelay(uint32_t frame_timestamp) {
  MutexLock lock(&mutex_);
  int target_delay_ms = TargetDelayInternal();

  if (current_delay_ms_ == 0) {
    // Not initialized, set current delay to target.
    current_delay_ms_ = target_delay_ms;
  } else if (target_delay_ms != current_delay_ms_) {
    int64_t delay_diff_ms =
        static_cast<int64_t>(target_delay_ms) - current_delay_ms_;
    // Never change the delay with more than 100 ms every second. If we're
    // changing the delay in too large steps we will get noticeable freezes. By
    // limiting the change we can increase the delay in smaller steps, which
    // will be experienced as the video is played in slow motion. When lowering
    // the delay the video will be played at a faster pace.
    int64_t max_change_ms = 0;
    if (frame_timestamp < 0x0000ffff && prev_frame_timestamp_ > 0xffff0000) {
      // wrap
      max_change_ms = kDelayMaxChangeMsPerS *
                      (frame_timestamp + (static_cast<int64_t>(1) << 32) -
                       prev_frame_timestamp_) /
                      90000;
    } else {
      max_change_ms = kDelayMaxChangeMsPerS *
                      (frame_timestamp - prev_frame_timestamp_) / 90000;
    }

    if (max_change_ms <= 0) {
      // Any changes less than 1 ms are truncated and will be postponed.
      // Negative change will be due to reordering and should be ignored.
      return;
    }
    delay_diff_ms = std::max(delay_diff_ms, -max_change_ms);
    delay_diff_ms = std::min(delay_diff_ms, max_change_ms);

    current_delay_ms_ = current_delay_ms_ + delay_diff_ms;
  }
  prev_frame_timestamp_ = frame_timestamp;
}

void VCMTiming::UpdateCurrentDelay(int64_t render_time_ms,
                                   int64_t actual_decode_time_ms) {
  MutexLock lock(&mutex_);
  uint32_t target_delay_ms = TargetDelayInternal();
  int64_t delayed_ms =
      actual_decode_time_ms -
      (render_time_ms - RequiredDecodeTimeMs() - render_delay_ms_);
  if (delayed_ms < 0) {
    return;
  }
  if (current_delay_ms_ + delayed_ms <= target_delay_ms) {
    current_delay_ms_ += delayed_ms;
  } else {
    current_delay_ms_ = target_delay_ms;
  }
}

void VCMTiming::StopDecodeTimer(uint32_t /*time_stamp*/,
                                int32_t decode_time_ms,
                                int64_t now_ms,
                                int64_t /*render_time_ms*/) {
  StopDecodeTimer(decode_time_ms, now_ms);
}

void VCMTiming::StopDecodeTimer(int32_t decode_time_ms, int64_t now_ms) {
  MutexLock lock(&mutex_);
  codec_timer_->AddTiming(decode_time_ms, now_ms);
  RTC_DCHECK_GE(decode_time_ms, 0);
  ++num_decoded_frames_;
}

void VCMTiming::IncomingTimestamp(uint32_t time_stamp, int64_t now_ms) {
  MutexLock lock(&mutex_);
  ts_extrapolator_->Update(now_ms, time_stamp);
}

int64_t VCMTiming::RenderTimeMs(uint32_t frame_timestamp,
                                int64_t now_ms) const {
  MutexLock lock(&mutex_);
  return RenderTimeMsInternal(frame_timestamp, now_ms);
}

void VCMTiming::SetLastDecodeScheduledTimestamp(
    int64_t last_decode_scheduled_ts) {
  MutexLock lock(&mutex_);
  last_decode_scheduled_ts_ = last_decode_scheduled_ts;
}

int64_t VCMTiming::RenderTimeMsInternal(uint32_t frame_timestamp,
                                        int64_t now_ms) const {
  constexpr int kLowLatencyRendererMaxPlayoutDelayMs = 500;
  if (min_playout_delay_ms_ == 0 &&
      (max_playout_delay_ms_ == 0 ||
       (low_latency_renderer_enabled_ &&
        max_playout_delay_ms_ <= kLowLatencyRendererMaxPlayoutDelayMs))) {
    // Render as soon as possible or with low-latency renderer algorithm.
    return 0;
  }
  // Note that TimestampExtrapolator::ExtrapolateLocalTime is not a const
  // method; it mutates the object's wraparound state.
  int64_t estimated_complete_time_ms =
      ts_extrapolator_->ExtrapolateLocalTime(frame_timestamp);
  if (estimated_complete_time_ms == -1) {
    estimated_complete_time_ms = now_ms;
  }

  // Make sure the actual delay stays in the range of `min_playout_delay_ms_`
  // and `max_playout_delay_ms_`.
  int actual_delay = std::max(current_delay_ms_, min_playout_delay_ms_);
  actual_delay = std::min(actual_delay, max_playout_delay_ms_);
  return estimated_complete_time_ms + actual_delay;
}

int VCMTiming::RequiredDecodeTimeMs() const {
  const int decode_time_ms = codec_timer_->RequiredDecodeTimeMs();
  RTC_DCHECK_GE(decode_time_ms, 0);
  return decode_time_ms;
}

int64_t VCMTiming::MaxWaitingTime(int64_t render_time_ms,
                                  int64_t now_ms,
                                  bool too_many_frames_queued) const {
  MutexLock lock(&mutex_);

  if (render_time_ms == 0 && zero_playout_delay_min_pacing_->us() > 0 &&
      min_playout_delay_ms_ == 0 && max_playout_delay_ms_ > 0) {
    // `render_time_ms` == 0 indicates that the frame should be decoded and
    // rendered as soon as possible. However, the decoder can be choked if too
    // many frames are sent at once. Therefore, limit the interframe delay to
    // |zero_playout_delay_min_pacing_| unless too many frames are queued in
    // which case the frames are sent to the decoder at once.
    if (too_many_frames_queued) {
      return 0;
    }
    int64_t earliest_next_decode_start_time =
        last_decode_scheduled_ts_ + zero_playout_delay_min_pacing_->ms();
    int64_t max_wait_time_ms = now_ms >= earliest_next_decode_start_time
                                   ? 0
                                   : earliest_next_decode_start_time - now_ms;
    return max_wait_time_ms;
  }
  return render_time_ms - now_ms - RequiredDecodeTimeMs() - render_delay_ms_;
}

int VCMTiming::TargetVideoDelay() const {
  MutexLock lock(&mutex_);
  return TargetDelayInternal();
}

int VCMTiming::TargetDelayInternal() const {
  return std::max(min_playout_delay_ms_,
                  jitter_delay_ms_ + RequiredDecodeTimeMs() + render_delay_ms_);
}

bool VCMTiming::GetTimings(int* max_decode_ms,
                           int* current_delay_ms,
                           int* target_delay_ms,
                           int* jitter_buffer_ms,
                           int* min_playout_delay_ms,
                           int* render_delay_ms) const {
  MutexLock lock(&mutex_);
  *max_decode_ms = RequiredDecodeTimeMs();
  *current_delay_ms = current_delay_ms_;
  *target_delay_ms = TargetDelayInternal();
  *jitter_buffer_ms = jitter_delay_ms_;
  *min_playout_delay_ms = min_playout_delay_ms_;
  *render_delay_ms = render_delay_ms_;
  return (num_decoded_frames_ > 0);
}

void VCMTiming::SetTimingFrameInfo(const TimingFrameInfo& info) {
  MutexLock lock(&mutex_);
  timing_frame_info_.emplace(info);
}

absl::optional<TimingFrameInfo> VCMTiming::GetTimingFrameInfo() {
  MutexLock lock(&mutex_);
  return timing_frame_info_;
}

void VCMTiming::SetMaxCompositionDelayInFrames(
    absl::optional<int> max_composition_delay_in_frames) {
  MutexLock lock(&mutex_);
  max_composition_delay_in_frames_ = max_composition_delay_in_frames;
}

absl::optional<int> VCMTiming::MaxCompositionDelayInFrames() const {
  MutexLock lock(&mutex_);
  return max_composition_delay_in_frames_;
}

}  // namespace webrtc