path: root/media/filters/source_buffer_range.cc

// Copyright 2014 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/filters/source_buffer_range.h"

#include <algorithm>

#include "media/base/timestamp_constants.h"

namespace media {

// Comparison operators for std::upper_bound() and std::lower_bound().
static bool CompareTimeDeltaToStreamParserBuffer(
    const DecodeTimestamp& decode_timestamp,
    const scoped_refptr<StreamParserBuffer>& buffer) {
  return decode_timestamp < buffer->GetDecodeTimestamp();
}
static bool CompareStreamParserBufferToTimeDelta(
    const scoped_refptr<StreamParserBuffer>& buffer,
    const DecodeTimestamp& decode_timestamp) {
  return buffer->GetDecodeTimestamp() < decode_timestamp;
}

bool SourceBufferRange::IsUncommonSameTimestampSequence(
    bool prev_is_keyframe,
    bool current_is_keyframe) {
  return current_is_keyframe && !prev_is_keyframe;
}

SourceBufferRange::SourceBufferRange(
    GapPolicy gap_policy,
    const BufferQueue& new_buffers,
    DecodeTimestamp range_start_time,
    const InterbufferDistanceCB& interbuffer_distance_cb)
    : gap_policy_(gap_policy),
      keyframe_map_index_base_(0),
      next_buffer_index_(-1),
      range_start_time_(range_start_time),
      interbuffer_distance_cb_(interbuffer_distance_cb),
      size_in_bytes_(0) {
  CHECK(!new_buffers.empty());
  DCHECK(new_buffers.front()->is_key_frame());
  DCHECK(!interbuffer_distance_cb.is_null());
  AppendBuffersToEnd(new_buffers, range_start_time_);
}

SourceBufferRange::~SourceBufferRange() {}

void SourceBufferRange::AppendBuffersToEnd(
    const BufferQueue& new_buffers,
    DecodeTimestamp new_buffers_group_start_timestamp) {
  CHECK(buffers_.empty() ||
        CanAppendBuffersToEnd(new_buffers, new_buffers_group_start_timestamp));
  DCHECK(range_start_time_ == kNoDecodeTimestamp() ||
         range_start_time_ <= new_buffers.front()->GetDecodeTimestamp());

  AdjustEstimatedDurationForNewAppend(new_buffers);

  for (BufferQueue::const_iterator itr = new_buffers.begin();
       itr != new_buffers.end();
       ++itr) {
    DCHECK((*itr)->GetDecodeTimestamp() != kNoDecodeTimestamp());
    buffers_.push_back(*itr);
    size_in_bytes_ += (*itr)->data_size();

    if ((*itr)->is_key_frame()) {
      keyframe_map_.insert(
          std::make_pair((*itr)->GetDecodeTimestamp(),
                         buffers_.size() - 1 + keyframe_map_index_base_));
    }
  }
}

void SourceBufferRange::AdjustEstimatedDurationForNewAppend(
    const BufferQueue& new_buffers) {
  if (buffers_.empty() || new_buffers.empty()) {
    return;
  }

  // If the last of the previously appended buffers contains estimated duration,
  // we now refine that estimate by taking the PTS delta from the first new
  // buffer being appended.
  const auto& last_appended_buffer = buffers_.back();
  if (last_appended_buffer->is_duration_estimated()) {
    base::TimeDelta timestamp_delta =
        new_buffers.front()->timestamp() - last_appended_buffer->timestamp();
    DCHECK(timestamp_delta > base::TimeDelta());
    if (last_appended_buffer->duration() != timestamp_delta) {
      DVLOG(1) << "Replacing estimated duration ("
               << last_appended_buffer->duration()
               << ") from previous range-end with derived duration ("
               << timestamp_delta << ").";
      last_appended_buffer->set_duration(timestamp_delta);
    }
  }
}

void SourceBufferRange::Seek(DecodeTimestamp timestamp) {
  DCHECK(CanSeekTo(timestamp));
  DCHECK(!keyframe_map_.empty());

  KeyframeMap::iterator result = GetFirstKeyframeAtOrBefore(timestamp);
  next_buffer_index_ = result->second - keyframe_map_index_base_;
  CHECK_LT(next_buffer_index_, static_cast<int>(buffers_.size()))
      << next_buffer_index_ << ", size = " << buffers_.size();
}

void SourceBufferRange::SeekAheadTo(DecodeTimestamp timestamp) {
  SeekAhead(timestamp, false);
}

void SourceBufferRange::SeekAheadPast(DecodeTimestamp timestamp) {
  SeekAhead(timestamp, true);
}

void SourceBufferRange::SeekAhead(DecodeTimestamp timestamp,
                                  bool skip_given_timestamp) {
  DCHECK(!keyframe_map_.empty());

  KeyframeMap::iterator result =
      GetFirstKeyframeAt(timestamp, skip_given_timestamp);

  // If there isn't a keyframe after |timestamp|, then seek to end and return
  // kNoTimestamp to signal such.
  if (result == keyframe_map_.end()) {
    next_buffer_index_ = -1;
    return;
  }
  next_buffer_index_ = result->second - keyframe_map_index_base_;
  DCHECK_LT(next_buffer_index_, static_cast<int>(buffers_.size()));
}

void SourceBufferRange::SeekToStart() {
  CHECK(!buffers_.empty());
  next_buffer_index_ = 0;
}

SourceBufferRange* SourceBufferRange::SplitRange(DecodeTimestamp timestamp) {
  CHECK(!buffers_.empty());

  // Find the first keyframe at or after |timestamp|.
  KeyframeMap::iterator new_beginning_keyframe =
      GetFirstKeyframeAt(timestamp, false);

  // If there is no keyframe after |timestamp|, we can't split the range.
  if (new_beginning_keyframe == keyframe_map_.end())
    return NULL;

  // Remove the data beginning at |keyframe_index| from |buffers_| and save it
  // into |removed_buffers|.
  int keyframe_index =
      new_beginning_keyframe->second - keyframe_map_index_base_;
  DCHECK_LT(keyframe_index, static_cast<int>(buffers_.size()));
  BufferQueue::iterator starting_point = buffers_.begin() + keyframe_index;
  BufferQueue removed_buffers(starting_point, buffers_.end());

  DecodeTimestamp new_range_start_timestamp = kNoDecodeTimestamp();
  if (GetStartTimestamp() < buffers_.front()->GetDecodeTimestamp() &&
      timestamp < removed_buffers.front()->GetDecodeTimestamp()) {
    // The split is in the gap between |range_start_time_| and the first buffer
    // of the new range so we should set the start time of the new range to
    // |timestamp| so we preserve part of the gap in the new range.
    new_range_start_timestamp = timestamp;
  }

  keyframe_map_.erase(new_beginning_keyframe, keyframe_map_.end());
  FreeBufferRange(starting_point, buffers_.end());

  // Create a new range with |removed_buffers|.
  SourceBufferRange* split_range =
      new SourceBufferRange(
          gap_policy_, removed_buffers, new_range_start_timestamp,
          interbuffer_distance_cb_);

  // If the next buffer position is now in |split_range|, update the state of
  // this range and |split_range| accordingly.
  if (next_buffer_index_ >= static_cast<int>(buffers_.size())) {
    split_range->next_buffer_index_ = next_buffer_index_ - keyframe_index;

    int split_range_next_buffer_index = split_range->next_buffer_index_;
    CHECK_GE(split_range_next_buffer_index, 0);
    // Note that a SourceBufferRange's |next_buffer_index_| can be the index
    // of a buffer one beyond what is currently in |buffers_|.
    CHECK_LE(split_range_next_buffer_index,
             static_cast<int>(split_range->buffers_.size()));

    ResetNextBufferPosition();
  }

  return split_range;
}

SourceBufferRange::BufferQueue::iterator SourceBufferRange::GetBufferItrAt(
    DecodeTimestamp timestamp,
    bool skip_given_timestamp) {
  return skip_given_timestamp
             ? std::upper_bound(buffers_.begin(),
                                buffers_.end(),
                                timestamp,
                                CompareTimeDeltaToStreamParserBuffer)
             : std::lower_bound(buffers_.begin(),
                                buffers_.end(),
                                timestamp,
                                CompareStreamParserBufferToTimeDelta);
}

SourceBufferRange::KeyframeMap::iterator
SourceBufferRange::GetFirstKeyframeAt(DecodeTimestamp timestamp,
                                      bool skip_given_timestamp) {
  return skip_given_timestamp ?
      keyframe_map_.upper_bound(timestamp) :
      keyframe_map_.lower_bound(timestamp);
}

SourceBufferRange::KeyframeMap::iterator
SourceBufferRange::GetFirstKeyframeAtOrBefore(DecodeTimestamp timestamp) {
  KeyframeMap::iterator result = keyframe_map_.lower_bound(timestamp);
  // lower_bound() returns the first element >= |timestamp|, so we want the
  // previous element if it did not return the element exactly equal to
  // |timestamp|.
  if (result != keyframe_map_.begin() &&
      (result == keyframe_map_.end() || result->first != timestamp)) {
    --result;
  }
  return result;
}

void SourceBufferRange::DeleteAll(BufferQueue* removed_buffers) {
  TruncateAt(buffers_.begin(), removed_buffers);
}

bool SourceBufferRange::TruncateAt(
    DecodeTimestamp timestamp, BufferQueue* removed_buffers,
    bool is_exclusive) {
  // Find the place in |buffers_| where we will begin deleting data.
  BufferQueue::iterator starting_point =
      GetBufferItrAt(timestamp, is_exclusive);
  return TruncateAt(starting_point, removed_buffers);
}

size_t SourceBufferRange::DeleteGOPFromFront(BufferQueue* deleted_buffers) {
  DCHECK(!buffers_.empty());
  DCHECK(!FirstGOPContainsNextBufferPosition());
  DCHECK(deleted_buffers);

  int buffers_deleted = 0;
  size_t total_bytes_deleted = 0;

  KeyframeMap::iterator front = keyframe_map_.begin();
  DCHECK(front != keyframe_map_.end());

  // Delete the keyframe at the start of |keyframe_map_|.
  keyframe_map_.erase(front);

  // Now we need to delete all the buffers that depend on the keyframe we've
  // just deleted.
  int end_index = keyframe_map_.size() > 0 ?
      keyframe_map_.begin()->second - keyframe_map_index_base_ :
      buffers_.size();

  // Delete buffers from the beginning of the buffered range up until (but not
  // including) the next keyframe.
  for (int i = 0; i < end_index; i++) {
    size_t bytes_deleted = buffers_.front()->data_size();
    DCHECK_GE(size_in_bytes_, bytes_deleted);
    size_in_bytes_ -= bytes_deleted;
    total_bytes_deleted += bytes_deleted;
    deleted_buffers->push_back(buffers_.front());
    buffers_.pop_front();
    ++buffers_deleted;
  }

  // Update |keyframe_map_index_base_| to account for the deleted buffers.
  keyframe_map_index_base_ += buffers_deleted;

  if (next_buffer_index_ > -1) {
    next_buffer_index_ -= buffers_deleted;
    CHECK_GE(next_buffer_index_, 0) << next_buffer_index_ << ", deleted "
                                    << buffers_deleted;
  }

  // Invalidate range start time if we've deleted the first buffer of the range.
  if (buffers_deleted > 0)
    range_start_time_ = kNoDecodeTimestamp();

  return total_bytes_deleted;
}

size_t SourceBufferRange::DeleteGOPFromBack(BufferQueue* deleted_buffers) {
  DCHECK(!buffers_.empty());
  DCHECK(!LastGOPContainsNextBufferPosition());
  DCHECK(deleted_buffers);

  // Remove the last GOP's keyframe from the |keyframe_map_|.
  KeyframeMap::iterator back = keyframe_map_.end();
  DCHECK_GT(keyframe_map_.size(), 0u);
  --back;

  // The index of the first buffer in the last GOP is equal to the new size of
  // |buffers_| after that GOP is deleted.
  size_t goal_size = back->second - keyframe_map_index_base_;
  keyframe_map_.erase(back);

  size_t total_bytes_deleted = 0;
  while (buffers_.size() != goal_size) {
    size_t bytes_deleted = buffers_.back()->data_size();
    DCHECK_GE(size_in_bytes_, bytes_deleted);
    size_in_bytes_ -= bytes_deleted;
    total_bytes_deleted += bytes_deleted;
    // We're removing buffers from the back, so push each removed buffer to the
    // front of |deleted_buffers| so that |deleted_buffers| are in nondecreasing
    // order.
    deleted_buffers->push_front(buffers_.back());
    buffers_.pop_back();
  }

  return total_bytes_deleted;
}

size_t SourceBufferRange::GetRemovalGOP(
    DecodeTimestamp start_timestamp, DecodeTimestamp end_timestamp,
    size_t total_bytes_to_free, DecodeTimestamp* removal_end_timestamp) {
  size_t bytes_removed = 0;

  KeyframeMap::iterator gop_itr = GetFirstKeyframeAt(start_timestamp, false);
  if (gop_itr == keyframe_map_.end())
    return 0;
  int keyframe_index = gop_itr->second - keyframe_map_index_base_;
  BufferQueue::iterator buffer_itr = buffers_.begin() + keyframe_index;
  KeyframeMap::iterator gop_end = keyframe_map_.end();
  if (end_timestamp < GetBufferedEndTimestamp())
    gop_end = GetFirstKeyframeAtOrBefore(end_timestamp);

  // Check if the removal range is within a GOP and skip the loop if so.
  // [keyframe]...[start_timestamp]...[end_timestamp]...[keyframe]
  KeyframeMap::iterator gop_itr_prev = gop_itr;
  if (gop_itr_prev != keyframe_map_.begin() && --gop_itr_prev == gop_end)
    gop_end = gop_itr;

  while (gop_itr != gop_end && bytes_removed < total_bytes_to_free) {
    ++gop_itr;

    size_t gop_size = 0;
    int next_gop_index = gop_itr == keyframe_map_.end() ?
        buffers_.size() : gop_itr->second - keyframe_map_index_base_;
    BufferQueue::iterator next_gop_start = buffers_.begin() + next_gop_index;
    for (; buffer_itr != next_gop_start; ++buffer_itr) {
      gop_size += (*buffer_itr)->data_size();
    }

    bytes_removed += gop_size;
  }
  if (bytes_removed > 0) {
    *removal_end_timestamp = gop_itr == keyframe_map_.end() ?
        GetBufferedEndTimestamp() : gop_itr->first;
  }
  return bytes_removed;
}

bool SourceBufferRange::FirstGOPEarlierThanMediaTime(
    DecodeTimestamp media_time) const {
  if (keyframe_map_.size() == 1u)
    return (GetBufferedEndTimestamp() <= media_time);

  KeyframeMap::const_iterator second_gop = keyframe_map_.begin();
  ++second_gop;
  return second_gop->first <= media_time;
}

bool SourceBufferRange::FirstGOPContainsNextBufferPosition() const {
  if (!HasNextBufferPosition())
    return false;

  // If there is only one GOP, it must contain the next buffer position.
  if (keyframe_map_.size() == 1u)
    return true;

  KeyframeMap::const_iterator second_gop = keyframe_map_.begin();
  ++second_gop;
  return next_buffer_index_ < second_gop->second - keyframe_map_index_base_;
}

bool SourceBufferRange::LastGOPContainsNextBufferPosition() const {
  if (!HasNextBufferPosition())
    return false;

  // If there is only one GOP, it must contain the next buffer position.
  if (keyframe_map_.size() == 1u)
    return true;

  KeyframeMap::const_iterator last_gop = keyframe_map_.end();
  --last_gop;
  return last_gop->second - keyframe_map_index_base_ <= next_buffer_index_;
}

void SourceBufferRange::FreeBufferRange(
    const BufferQueue::iterator& starting_point,
    const BufferQueue::iterator& ending_point) {
  for (BufferQueue::iterator itr = starting_point;
       itr != ending_point; ++itr) {
    size_t itr_data_size = static_cast<size_t>((*itr)->data_size());
    DCHECK_GE(size_in_bytes_, itr_data_size);
    size_in_bytes_ -= itr_data_size;
  }
  buffers_.erase(starting_point, ending_point);
}

bool SourceBufferRange::TruncateAt(
    const BufferQueue::iterator& starting_point, BufferQueue* removed_buffers) {
  DCHECK(!removed_buffers || removed_buffers->empty());

  // Return if we're not deleting anything.
  if (starting_point == buffers_.end())
    return buffers_.empty();

  // Reset the next buffer index if we will be deleting the buffer that's next
  // in sequence.
  if (HasNextBufferPosition()) {
    DecodeTimestamp next_buffer_timestamp = GetNextTimestamp();
    if (next_buffer_timestamp == kNoDecodeTimestamp() ||
        next_buffer_timestamp >= (*starting_point)->GetDecodeTimestamp()) {
      if (HasNextBuffer() && removed_buffers) {
        int starting_offset = starting_point - buffers_.begin();
        int next_buffer_offset = next_buffer_index_ - starting_offset;
        DCHECK_GE(next_buffer_offset, 0);
        BufferQueue saved(starting_point + next_buffer_offset, buffers_.end());
        removed_buffers->swap(saved);
      }
      ResetNextBufferPosition();
    }
  }

  // Remove keyframes from |starting_point| onward.
  KeyframeMap::iterator starting_point_keyframe =
      keyframe_map_.lower_bound((*starting_point)->GetDecodeTimestamp());
  keyframe_map_.erase(starting_point_keyframe, keyframe_map_.end());

  // Remove everything from |starting_point| onward.
  FreeBufferRange(starting_point, buffers_.end());
  return buffers_.empty();
}

bool SourceBufferRange::GetNextBuffer(
    scoped_refptr<StreamParserBuffer>* out_buffer) {
  if (!HasNextBuffer())
    return false;

  *out_buffer = buffers_[next_buffer_index_];
  next_buffer_index_++;
  return true;
}

bool SourceBufferRange::HasNextBuffer() const {
  return next_buffer_index_ >= 0 &&
      next_buffer_index_ < static_cast<int>(buffers_.size());
}

int SourceBufferRange::GetNextConfigId() const {
  CHECK(HasNextBuffer()) << next_buffer_index_;
  // If the next buffer is an audio splice frame, the next effective config id
  // comes from the first fade out preroll buffer.
  return buffers_[next_buffer_index_]->GetSpliceBufferConfigId(0);
}

DecodeTimestamp SourceBufferRange::GetNextTimestamp() const {
  CHECK(!buffers_.empty()) << next_buffer_index_;
  CHECK(HasNextBufferPosition()) << next_buffer_index_
                                 << ", size=" << buffers_.size();

  if (next_buffer_index_ >= static_cast<int>(buffers_.size())) {
    return kNoDecodeTimestamp();
  }

  return buffers_[next_buffer_index_]->GetDecodeTimestamp();
}

bool SourceBufferRange::HasNextBufferPosition() const {
  return next_buffer_index_ >= 0;
}

void SourceBufferRange::ResetNextBufferPosition() {
  next_buffer_index_ = -1;
}

void SourceBufferRange::AppendRangeToEnd(const SourceBufferRange& range,
                                         bool transfer_current_position) {
  DCHECK(CanAppendRangeToEnd(range));
  DCHECK(!buffers_.empty());

  if (transfer_current_position && range.next_buffer_index_ >= 0)
    next_buffer_index_ = range.next_buffer_index_ + buffers_.size();

  AppendBuffersToEnd(range.buffers_, kNoDecodeTimestamp());
}

bool SourceBufferRange::CanAppendRangeToEnd(
    const SourceBufferRange& range) const {
  return CanAppendBuffersToEnd(range.buffers_, kNoDecodeTimestamp());
}

bool SourceBufferRange::CanAppendBuffersToEnd(
    const BufferQueue& buffers,
    DecodeTimestamp new_buffers_group_start_timestamp) const {
  DCHECK(!buffers_.empty());
  if (new_buffers_group_start_timestamp == kNoDecodeTimestamp()) {
    return IsNextInSequence(buffers.front()->GetDecodeTimestamp());
  }
  DCHECK(new_buffers_group_start_timestamp >= GetEndTimestamp());
  DCHECK(buffers.front()->GetDecodeTimestamp() >=
         new_buffers_group_start_timestamp);
  return IsNextInSequence(new_buffers_group_start_timestamp);
}

bool SourceBufferRange::BelongsToRange(DecodeTimestamp timestamp) const {
  DCHECK(!buffers_.empty());

  return (IsNextInSequence(timestamp) ||
          (GetStartTimestamp() <= timestamp && timestamp <= GetEndTimestamp()));
}

bool SourceBufferRange::CanSeekTo(DecodeTimestamp timestamp) const {
  DecodeTimestamp start_timestamp =
      std::max(DecodeTimestamp(), GetStartTimestamp() - GetFudgeRoom());
  return !keyframe_map_.empty() && start_timestamp <= timestamp &&
      timestamp < GetBufferedEndTimestamp();
}

bool SourceBufferRange::CompletelyOverlaps(
    const SourceBufferRange& range) const {
  return GetStartTimestamp() <= range.GetStartTimestamp() &&
      GetEndTimestamp() >= range.GetEndTimestamp();
}

bool SourceBufferRange::EndOverlaps(const SourceBufferRange& range) const {
  return range.GetStartTimestamp() <= GetEndTimestamp() &&
      GetEndTimestamp() < range.GetEndTimestamp();
}

DecodeTimestamp SourceBufferRange::GetStartTimestamp() const {
  DCHECK(!buffers_.empty());
  DecodeTimestamp start_timestamp = range_start_time_;
  if (start_timestamp == kNoDecodeTimestamp())
    start_timestamp = buffers_.front()->GetDecodeTimestamp();
  return start_timestamp;
}

DecodeTimestamp SourceBufferRange::GetEndTimestamp() const {
  DCHECK(!buffers_.empty());
  return buffers_.back()->GetDecodeTimestamp();
}

DecodeTimestamp SourceBufferRange::GetBufferedEndTimestamp() const {
  DCHECK(!buffers_.empty());
  base::TimeDelta duration = buffers_.back()->duration();
  if (duration == kNoTimestamp() || duration == base::TimeDelta())
    duration = GetApproximateDuration();
  return GetEndTimestamp() + duration;
}

DecodeTimestamp SourceBufferRange::NextKeyframeTimestamp(
    DecodeTimestamp timestamp) {
  DCHECK(!keyframe_map_.empty());

  if (timestamp < GetStartTimestamp() || timestamp >= GetBufferedEndTimestamp())
    return kNoDecodeTimestamp();

  KeyframeMap::iterator itr = GetFirstKeyframeAt(timestamp, false);
  if (itr == keyframe_map_.end())
    return kNoDecodeTimestamp();

  // If the timestamp is inside the gap between the start of the coded frame
  // group and the first buffer, then just pretend there is a keyframe at the
  // specified timestamp.
  if (itr == keyframe_map_.begin() && timestamp > range_start_time_ &&
      timestamp < itr->first) {
    return timestamp;
  }

  return itr->first;
}

DecodeTimestamp SourceBufferRange::KeyframeBeforeTimestamp(
    DecodeTimestamp timestamp) {
  DCHECK(!keyframe_map_.empty());

  if (timestamp < GetStartTimestamp() || timestamp >= GetBufferedEndTimestamp())
    return kNoDecodeTimestamp();

  return GetFirstKeyframeAtOrBefore(timestamp)->first;
}

bool SourceBufferRange::IsNextInSequence(DecodeTimestamp timestamp) const {
  DecodeTimestamp end = buffers_.back()->GetDecodeTimestamp();
  return (end == timestamp ||
          (end < timestamp &&
           (gap_policy_ == ALLOW_GAPS || timestamp <= end + GetFudgeRoom())));
}

base::TimeDelta SourceBufferRange::GetFudgeRoom() const {
  // Because we do not know exactly when is the next timestamp, any buffer
  // that starts within 2x the approximate duration of a buffer is considered
  // within this range.
  return 2 * GetApproximateDuration();
}

base::TimeDelta SourceBufferRange::GetApproximateDuration() const {
  base::TimeDelta max_interbuffer_distance = interbuffer_distance_cb_.Run();
  DCHECK(max_interbuffer_distance != kNoTimestamp());
  return max_interbuffer_distance;
}

bool SourceBufferRange::GetBuffersInRange(DecodeTimestamp start,
                                          DecodeTimestamp end,
                                          BufferQueue* buffers) {
  // Find the nearest buffer with a decode timestamp <= start.
  const DecodeTimestamp first_timestamp = KeyframeBeforeTimestamp(start);
  if (first_timestamp == kNoDecodeTimestamp())
    return false;

  // Find all buffers involved in the range.
  const size_t previous_size = buffers->size();
  for (BufferQueue::iterator it = GetBufferItrAt(first_timestamp, false);
       it != buffers_.end();
       ++it) {
    const scoped_refptr<StreamParserBuffer>& buffer = *it;
    // Buffers without duration are not supported, so bail if we encounter any.
    if (buffer->duration() == kNoTimestamp() ||
        buffer->duration() <= base::TimeDelta()) {
      return false;
    }
    if (buffer->end_of_stream() ||
        buffer->timestamp() >= end.ToPresentationTime()) {
      break;
    }

    if (buffer->timestamp() + buffer->duration() <= start.ToPresentationTime())
      continue;
    buffers->push_back(buffer);
  }
  return previous_size < buffers->size();
}

}  // namespace media