118 lines
4.1 KiB
C++
118 lines
4.1 KiB
C++
// Copyright 2014 Google LLC. All rights reserved.
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//
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file or at
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// https://developers.google.com/open-source/licenses/bsd
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#include <packager/mpd/base/bandwidth_estimator.h>
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#include <algorithm>
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#include <cmath>
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#include <numeric>
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#include <absl/log/check.h>
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#include <absl/log/log.h>
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#include <packager/macros/logging.h>
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namespace shaka {
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BandwidthEstimator::BandwidthEstimator() = default;
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BandwidthEstimator::~BandwidthEstimator() = default;
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void BandwidthEstimator::AddBlock(uint64_t size_in_bytes, double duration) {
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if (size_in_bytes == 0 || duration == 0) {
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LOG(WARNING) << "Ignore block with size=" << size_in_bytes
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<< ", duration=" << duration;
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return;
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}
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const int kBitsInByte = 8;
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const uint64_t size_in_bits = size_in_bytes * kBitsInByte;
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total_size_in_bits_ += size_in_bits;
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total_duration_ += duration;
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const size_t kTargetDurationThreshold = 10;
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if (initial_blocks_.size() < kTargetDurationThreshold) {
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initial_blocks_.push_back({size_in_bits, duration});
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return;
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}
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if (target_block_duration_ == 0) {
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// Use the average duration as the target block duration. It will be used
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// to filter small blocks from bandwidth calculation.
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target_block_duration_ = GetAverageBlockDuration();
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for (const Block& block : initial_blocks_) {
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max_bitrate_ =
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std::max(max_bitrate_, GetBitrate(block, target_block_duration_));
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}
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return;
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}
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max_bitrate_ = std::max(max_bitrate_, GetBitrate({size_in_bits, duration},
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target_block_duration_));
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}
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uint64_t BandwidthEstimator::Estimate() const {
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if (total_duration_ == 0)
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return 0;
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return static_cast<uint64_t>(ceil(total_size_in_bits_ / total_duration_));
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}
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uint64_t BandwidthEstimator::Max() const {
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if (max_bitrate_ != 0)
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return max_bitrate_;
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// We don't have the |target_block_duration_| yet. Calculate a target
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// duration from the current available blocks.
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DCHECK(target_block_duration_ == 0);
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const double target_block_duration = GetAverageBlockDuration();
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// Calculate maximum bitrate with the target duration calculated above.
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uint64_t max_bitrate = 0;
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for (const Block& block : initial_blocks_) {
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max_bitrate =
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std::max(max_bitrate, GetBitrate(block, target_block_duration));
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}
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return max_bitrate;
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}
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double BandwidthEstimator::GetAverageBlockDuration() const {
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if (initial_blocks_.empty())
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return 0.0;
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const double sum =
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std::accumulate(initial_blocks_.begin(), initial_blocks_.end(), 0.0,
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[](double duration, const Block& block) {
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return duration + block.duration;
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});
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return sum / initial_blocks_.size();
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}
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uint64_t BandwidthEstimator::GetBitrate(const Block& block,
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double target_block_duration) const {
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if (block.duration < 0.5 * target_block_duration) {
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// https://tools.ietf.org/html/rfc8216#section-4.1
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// The peak segment bit rate of a Media Playlist is the largest bit rate of
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// any continuous set of segments whose total duration is between 0.5
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// and 1.5 times the target duration.
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// Only the short segments are excluded here as our media playlist generator
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// sets the target duration in the playlist to the largest segment duration.
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// So although the segment duration could be 1.5 times the user provided
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// segment duration, it will never be larger than the actual target
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// duration.
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//
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// We also apply the same exclusion to the bandwidth computation for DASH as
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// the bitrate for the short segment is not a good signal for peak
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// bandwidth.
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// See https://github.com/shaka-project/shaka-packager/issues/498 for
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// details.
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VLOG(1) << "Exclude short segment (duration " << block.duration
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<< ", target_duration " << target_block_duration
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<< ") in peak bandwidth computation.";
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return 0;
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}
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return static_cast<uint64_t>(ceil(block.size_in_bits / block.duration));
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}
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} // namespace shaka
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