Estimate target duration in bandwidth calculation from initial blocks

We used to use the target segment duration provided by the user.
Unfortunately that does not work for iframe only playlist which
the target duration is effectively equal to the GOP duration.

In the new approach, we estimate the target duration from the initial
few blocks (10 blocks right now).

Fixes #610.

Change-Id: Ie8bf943e157149ca7ed3b9382fe0a1088d0774e2

packager/hls/base/media_playlist.cc

@@ -340,8 +340,7 @@ MediaPlaylist::MediaPlaylist(const HlsParams& hls_params,
     : hls_params_(hls_params),
       file_name_(file_name),
       name_(name),
-      group_id_(group_id),
-      bandwidth_estimator_(hls_params_.target_segment_duration) {}
+      group_id_(group_id) {}
 
 MediaPlaylist::~MediaPlaylist() {}
 

packager/hls/public/hls_params.h

@@ -52,11 +52,7 @@ struct HlsParams {
   /// i.e. subtitles or close-captions.
   std::string default_text_language;
   /// This is the target segment duration requested by the user. The actual
-  /// segment duration may be different to the target segment duration.
-  /// This parameter is included here to for bandwidth estimator to exclude the
-  /// segments with duration less than half of the target duration from
-  /// bandwidth estimation. See
-  /// https://github.com/google/shaka-packager/issues/498 for details. It will
+  /// segment duration may be different to the target segment duration. It will
   /// be populated from segment duration specified in ChunkingParams if not
   /// specified.
   double target_segment_duration = 0;

packager/mpd/base/bandwidth_estimator.cc

@@ -8,13 +8,13 @@
 
 #include <algorithm>
 #include <cmath>
+#include <numeric>
 
 #include "packager/base/logging.h"
 
 namespace shaka {
 
-BandwidthEstimator::BandwidthEstimator(double target_segment_duration)
-    : target_segment_duration_(target_segment_duration) {}
+BandwidthEstimator::BandwidthEstimator() = default;
 
 BandwidthEstimator::~BandwidthEstimator() = default;
 
@@ -28,12 +28,66 @@ void BandwidthEstimator::AddBlock(uint64_t size_in_bytes, double duration) {
   const int kBitsInByte = 8;
   const uint64_t size_in_bits = size_in_bytes * kBitsInByte;
   total_size_in_bits_ += size_in_bits;
-
   total_duration_ += duration;
 
-  const uint64_t bitrate = static_cast<uint64_t>(ceil(size_in_bits / duration));
+  const size_t kTargetDurationThreshold = 10;
+  if (initial_blocks_.size() < kTargetDurationThreshold) {
+    initial_blocks_.push_back({size_in_bits, duration});
+    return;
+  }
 
-  if (duration < 0.5 * target_segment_duration_) {
+  if (target_block_duration_ == 0) {
+    // Use the average duration as the target block duration. It will be used
+    // to filter small blocks from bandwidth calculation.
+    target_block_duration_ = GetAverageBlockDuration();
+    for (const Block& block : initial_blocks_) {
+      max_bitrate_ =
+          std::max(max_bitrate_, GetBitrate(block, target_block_duration_));
+    }
+    return;
+  }
+  max_bitrate_ = std::max(max_bitrate_, GetBitrate({size_in_bits, duration},
+                                                   target_block_duration_));
+}
+
+uint64_t BandwidthEstimator::Estimate() const {
+  if (total_duration_ == 0)
+    return 0;
+  return static_cast<uint64_t>(ceil(total_size_in_bits_ / total_duration_));
+}
+
+uint64_t BandwidthEstimator::Max() const {
+  if (max_bitrate_ != 0)
+    return max_bitrate_;
+
+  // We don't have the |target_block_duration_| yet. Calculate a target
+  // duration from the current available blocks.
+  DCHECK(target_block_duration_ == 0);
+  const double target_block_duration = GetAverageBlockDuration();
+
+  // Calculate maximum bitrate with the target duration calculated above.
+  uint64_t max_bitrate = 0;
+  for (const Block& block : initial_blocks_) {
+    max_bitrate =
+        std::max(max_bitrate, GetBitrate(block, target_block_duration));
+  }
+  return max_bitrate;
+}
+
+double BandwidthEstimator::GetAverageBlockDuration() const {
+  if (initial_blocks_.empty())
+    return 0.0;
+  const double sum =
+      std::accumulate(initial_blocks_.begin(), initial_blocks_.end(), 0.0,
+                      [](double duration, const Block& block) {
+                        return duration + block.duration;
+                      });
+  return sum / initial_blocks_.size();
+}
+
+uint64_t BandwidthEstimator::GetBitrate(const Block& block,
+                                        double target_block_duration) const {
+  if (block.duration < 0.5 * target_block_duration) {
     // https://tools.ietf.org/html/rfc8216#section-4.1
     // The peak segment bit rate of a Media Playlist is the largest bit rate of
     // any continuous set of segments whose total duration is between 0.5
@@ -44,29 +98,16 @@ void BandwidthEstimator::AddBlock(uint64_t size_in_bytes, double duration) {
     // segment duration, it will never be larger than the actual target
     // duration.
     //
-    // TODO(kqyang): Review if we can just stick to the user provided segment
-    // duration as our target duration.
-    //
     // We also apply the same exclusion to the bandwidth computation for DASH as
     // the bitrate for the short segment is not a good signal for peak
     // bandwidth.
     // See https://github.com/google/shaka-packager/issues/498 for details.
-    VLOG(1) << "Exclude short segment (duration " << duration
-            << ", target_duration " << target_segment_duration_
+    VLOG(1) << "Exclude short segment (duration " << block.duration
+            << ", target_duration " << target_block_duration
             << ") in peak bandwidth computation.";
-    return;
+    return 0.0;
   }
-  max_bitrate_ = std::max(bitrate, max_bitrate_);
-}
-
-uint64_t BandwidthEstimator::Estimate() const {
-  if (total_duration_ == 0)
-    return 0;
-  return static_cast<uint64_t>(ceil(total_size_in_bits_ / total_duration_));
-}
-
-uint64_t BandwidthEstimator::Max() const {
-  return max_bitrate_;
+  return static_cast<uint64_t>(ceil(block.size_in_bits / block.duration));
 }
 
 }  // namespace shaka

packager/mpd/base/bandwidth_estimator.h

@@ -9,11 +9,13 @@
 
 #include <stdint.h>
 
+#include <vector>
+
 namespace shaka {
 
 class BandwidthEstimator {
  public:
-  explicit BandwidthEstimator(double target_segment_duration);
+  BandwidthEstimator();
   ~BandwidthEstimator();
 
   /// @param size is the size of the block in bytes. Should be positive.
@@ -28,14 +30,29 @@ class BandwidthEstimator {
 
   /// @return The max bandwidth, in bits per second, of the number of blocks
   ///         specified in the constructor. The value is rounded up to the
-  ///         nearest integer.
+  ///         nearest integer. Note that small blocks w.r.t.
+  ///         |target_block_duration| are not counted.
   uint64_t Max() const;
 
  private:
   BandwidthEstimator(const BandwidthEstimator&) = delete;
   BandwidthEstimator& operator=(const BandwidthEstimator&) = delete;
 
-  const double target_segment_duration_ = 0;
+  struct Block {
+    uint64_t size_in_bits;
+    double duration;
+  };
+  // Return the average block duration of the blocks in |initial_blocks_|.
+  double GetAverageBlockDuration() const;
+  // Return the bitrate of the block. Note that a bitrate of 0 is returned if
+  // the block duration is less than 50% of target block duration.
+  uint64_t GetBitrate(const Block& block, double target_block_duration) const;
+
+  std::vector<Block> initial_blocks_;
+  // Target block duration will be estimated from the average duration of the
+  // initial blocks.
+  double target_block_duration_ = 0;
+
   uint64_t total_size_in_bits_ = 0;
   double total_duration_ = 0;
   uint64_t max_bitrate_ = 0;

packager/mpd/base/bandwidth_estimator_unittest.cc

@@ -16,7 +16,7 @@ const uint64_t kBitsInByte = 8;
 
 TEST(BandwidthEstimatorTest, AllBlocks) {
   const double kDuration = 1.0;
-  BandwidthEstimator be(kDuration);
+  BandwidthEstimator be;
   const uint64_t kNumBlocksToAdd = 100;
   uint64_t total_bytes = 0;
   for (uint64_t i = 1; i <= kNumBlocksToAdd; ++i) {
@@ -31,9 +31,9 @@ TEST(BandwidthEstimatorTest, AllBlocks) {
   EXPECT_EQ(kMax, be.Max());
 }
 
-TEST(BandwidthEstimatorTest, ExcludeShortSegments) {
+TEST(BandwidthEstimatorTest, ExcludeShortBlocks) {
   const double kDuration = 1.0;
-  BandwidthEstimator be(kDuration);
+  BandwidthEstimator be;
 
   // Add 4 blocks with duration 0.1, 0.8, 1.8 and 0.2 respectively. The first
   // and the last blocks are excluded as they are too short.
@@ -46,4 +46,21 @@ TEST(BandwidthEstimatorTest, ExcludeShortSegments) {
   EXPECT_EQ(kExpectedMax, be.Max());
 }
 
+TEST(BandwidthEstimatorTest, ExcludeShortBlocksMore) {
+  const double kDuration = 1.0;
+  BandwidthEstimator be;
+
+  for (int k = 0; k < 100; k++) {
+    // Add 4 blocks with duration 0.1, 0.8, 1.8 and 0.2 respectively. The first
+    // and the last blocks are excluded as they are too short.
+    be.AddBlock(1, 0.1 * kDuration);
+    be.AddBlock(1, 0.8 * kDuration);
+    be.AddBlock(1, 1.8 * kDuration);
+    be.AddBlock(1, 0.2 * kDuration);
+  }
+
+  const uint64_t kExpectedMax = 1 / 0.8 * kBitsInByte;
+  EXPECT_EQ(kExpectedMax, be.Max());
+}
+
 } // namespace shaka

packager/mpd/base/representation.cc

@@ -88,7 +88,6 @@ Representation::Representation(
     std::unique_ptr<RepresentationStateChangeListener> state_change_listener)
     : media_info_(media_info),
       id_(id),
-      bandwidth_estimator_(mpd_options.mpd_params.target_segment_duration),
       mpd_options_(mpd_options),
       state_change_listener_(std::move(state_change_listener)),
       allow_approximate_segment_timeline_(

packager/mpd/base/representation_unittest.cc

@@ -443,9 +443,6 @@ std::string GetDefaultMediaInfo() {
 
 class SegmentTemplateTest : public RepresentationTest {
  public:
-  SegmentTemplateTest()
-      : bandwidth_estimator_(kTargetSegmentDurationInSeconds) {}
-
   void SetUp() override {
     mpd_options_.mpd_type = MpdType::kDynamic;
     representation_ =

packager/mpd/public/mpd_params.h

@@ -77,10 +77,8 @@ struct MpdParams {
   /// This is the target segment duration requested by the user. The actual
   /// segment duration may be different to the target segment duration.
   /// This parameter is included here to calculate the approximate
-  /// SegmentTimeline if it is enabled. It is also used by the bandwidth
-  /// estimator to exclude the segments with duration less than half of the
-  /// target duration from bandwidth estimation. It will be populated from
-  /// segment duration specified in ChunkingParams if not specified.
+  /// SegmentTimeline if it is enabled. It will be populated from segment
+  /// duration specified in ChunkingParams if not specified.
   double target_segment_duration = 0;
 };