webm_cluster_parser.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 "packager/media/formats/webm/webm_cluster_parser.h"

#include <vector>

#include "packager/base/logging.h"
#include "packager/base/sys_byteorder.h"
#include "packager/media/base/decrypt_config.h"
#include "packager/media/base/timestamp.h"
#include "packager/media/filters/webvtt_util.h"
#include "packager/media/formats/webm/webm_constants.h"
#include "packager/media/formats/webm/webm_crypto_helpers.h"
#include "packager/media/formats/webm/webm_webvtt_parser.h"

// Logs only while |count| < |max|, increments |count| for each log, and warns
// in the log if |count| has just reached |max|.
#define LIMITED_LOG(level, count, max)                         \
  LOG_IF(level, (count) < (max))                               \
      << (((count) + 1 == (max))                               \
              ? "(Log limit reached. Further similar entries " \
                "may be suppressed): "                         \
              : "")
#define LIMITED_DLOG(level, count, max)                        \
  DLOG_IF(level, (count) < (max))                              \
      << (((count) + 1 == (max))                               \
              ? "(Log limit reached. Further similar entries " \
                "may be suppressed): "                         \
              : "")

namespace {
const int64_t kMicrosecondsPerMillisecond = 1000;
}  // namespace

namespace edash_packager {
namespace media {

const uint16_t WebMClusterParser::kOpusFrameDurationsMu[] = {
    10000, 20000, 40000, 60000, 10000, 20000, 40000, 60000, 10000, 20000, 40000,
    60000, 10000, 20000, 10000, 20000, 2500,  5000,  10000, 20000, 2500,  5000,
    10000, 20000, 2500,  5000,  10000, 20000, 2500,  5000,  10000, 20000};

enum {
  // Limits the number of LOG() calls in the path of reading encoded
  // duration to avoid spamming for corrupted data.
  kMaxDurationErrorLogs = 10,
  // Limits the number of LOG() calls warning the user that buffer
  // durations have been estimated.
  kMaxDurationEstimateLogs = 10,
};

WebMClusterParser::WebMClusterParser(
    int64_t timecode_scale,
    int audio_track_num,
    int64_t audio_default_duration,
    int video_track_num,
    int64_t video_default_duration,
    const WebMTracksParser::TextTracks& text_tracks,
    const std::set<int64_t>& ignored_tracks,
    const std::string& audio_encryption_key_id,
    const std::string& video_encryption_key_id,
    const AudioCodec audio_codec,
    const MediaParser::NewSampleCB& new_sample_cb)
    : timecode_multiplier_(timecode_scale / 1000.0),
      ignored_tracks_(ignored_tracks),
      audio_encryption_key_id_(audio_encryption_key_id),
      video_encryption_key_id_(video_encryption_key_id),
      audio_codec_(audio_codec),
      parser_(kWebMIdCluster, this),
      cluster_start_time_(kNoTimestamp),
      audio_(audio_track_num, false, audio_default_duration, new_sample_cb),
      video_(video_track_num, true, video_default_duration, new_sample_cb) {
  for (WebMTracksParser::TextTracks::const_iterator it = text_tracks.begin();
       it != text_tracks.end();
       ++it) {
    text_track_map_.insert(std::make_pair(
        it->first, Track(it->first, false, kNoTimestamp, new_sample_cb)));
  }
}

WebMClusterParser::~WebMClusterParser() {}

void WebMClusterParser::Reset() {
  last_block_timecode_ = -1;
  cluster_timecode_ = -1;
  cluster_start_time_ = kNoTimestamp;
  cluster_ended_ = false;
  parser_.Reset();
  audio_.Reset();
  video_.Reset();
  ResetTextTracks();
}

int WebMClusterParser::Parse(const uint8_t* buf, int size) {
  int result = parser_.Parse(buf, size);

  if (result < 0) {
    cluster_ended_ = false;
    return result;
  }

  cluster_ended_ = parser_.IsParsingComplete();
  if (cluster_ended_) {
    audio_.ApplyDurationEstimateIfNeeded();
    video_.ApplyDurationEstimateIfNeeded();

    // If there were no buffers in this cluster, set the cluster start time to
    // be the |cluster_timecode_|.
    if (cluster_start_time_ == kNoTimestamp) {
      // If the cluster did not even have a |cluster_timecode_|, signal parse
      // error.
      if (cluster_timecode_ < 0)
        return -1;

      cluster_start_time_ = cluster_timecode_ * timecode_multiplier_;
    }

    // Reset the parser if we're done parsing so that
    // it is ready to accept another cluster on the next
    // call.
    parser_.Reset();

    last_block_timecode_ = -1;
    cluster_timecode_ = -1;
  }

  return result;
}

int64_t WebMClusterParser::TryGetEncodedAudioDuration(
    const uint8_t* data,
    int size) {

  // Duration is currently read assuming the *entire* stream is unencrypted.
  // The special "Signal Byte" prepended to Blocks in encrypted streams is
  // assumed to not be present.
  // TODO: Consider parsing "Signal Byte" for encrypted streams to return
  // duration for any unencrypted blocks.

  if (audio_codec_ == kCodecOpus) {
    return ReadOpusDuration(data, size);
  }

  // TODO: Implement duration reading for Vorbis. See motivations in
  // http://crbug.com/396634.

  return kNoTimestamp;
}

int64_t WebMClusterParser::ReadOpusDuration(const uint8_t* data, int size) {
  // Masks and constants for Opus packets. See
  // https://tools.ietf.org/html/rfc6716#page-14
  static const uint8_t kTocConfigMask = 0xf8;
  static const uint8_t kTocFrameCountCodeMask = 0x03;
  static const uint8_t kFrameCountMask = 0x3f;
  static const int64_t kPacketDurationMax = 120;

  if (size < 1) {
    LIMITED_DLOG(INFO, num_duration_errors_, kMaxDurationErrorLogs)
        << "Invalid zero-byte Opus packet; demuxed block duration may be "
           "imprecise.";
    return kNoTimestamp;
  }

  // Frame count type described by last 2 bits of Opus TOC byte.
  int frame_count_type = data[0] & kTocFrameCountCodeMask;

  int frame_count = 0;
  switch (frame_count_type) {
    case 0:
      frame_count = 1;
      break;
    case 1:
    case 2:
      frame_count = 2;
      break;
    case 3:
      // Type 3 indicates an arbitrary frame count described in the next byte.
      if (size < 2) {
        LIMITED_DLOG(INFO, num_duration_errors_, kMaxDurationErrorLogs)
            << "Second byte missing from 'Code 3' Opus packet; demuxed block "
               "duration may be imprecise.";
        return kNoTimestamp;
      }

      frame_count = data[1] & kFrameCountMask;

      if (frame_count == 0) {
        LIMITED_DLOG(INFO, num_duration_errors_, kMaxDurationErrorLogs)
            << "Illegal 'Code 3' Opus packet with frame count zero; demuxed "
               "block duration may be imprecise.";
        return kNoTimestamp;
      }

      break;
    default:
      LIMITED_DLOG(INFO, num_duration_errors_, kMaxDurationErrorLogs)
          << "Unexpected Opus frame count type: " << frame_count_type << "; "
          << "demuxed block duration may be imprecise.";
      return kNoTimestamp;
  }

  int opusConfig = (data[0] & kTocConfigMask) >> 3;
  CHECK_GE(opusConfig, 0);
  CHECK_LT(opusConfig, static_cast<int>(arraysize(kOpusFrameDurationsMu)));

  DCHECK_GT(frame_count, 0);
  int64_t duration = kOpusFrameDurationsMu[opusConfig] * frame_count;

  if (duration > kPacketDurationMax) {
    // Intentionally allowing packet to pass through for now. Decoder should
    // either handle or fail gracefully. LOG as breadcrumbs in case
    // things go sideways.
    LIMITED_DLOG(INFO, num_duration_errors_, kMaxDurationErrorLogs)
        << "Warning, demuxed Opus packet with encoded duration: "
        << duration << "ms. Should be no greater than "
        << kPacketDurationMax << "ms.";
  }

  return duration;
}

WebMParserClient* WebMClusterParser::OnListStart(int id) {
  if (id == kWebMIdCluster) {
    cluster_timecode_ = -1;
    cluster_start_time_ = kNoTimestamp;
  } else if (id == kWebMIdBlockGroup) {
    block_data_.reset();
    block_data_size_ = -1;
    block_duration_ = -1;
    discard_padding_ = -1;
    discard_padding_set_ = false;
  } else if (id == kWebMIdBlockAdditions) {
    block_add_id_ = -1;
    block_additional_data_.reset();
    block_additional_data_size_ = 0;
  }

  return this;
}

bool WebMClusterParser::OnListEnd(int id) {
  if (id != kWebMIdBlockGroup)
    return true;

  // Make sure the BlockGroup actually had a Block.
  if (block_data_size_ == -1) {
    LOG(ERROR) << "Block missing from BlockGroup.";
    return false;
  }

  bool result = ParseBlock(false, block_data_.get(), block_data_size_,
                           block_additional_data_.get(),
                           block_additional_data_size_, block_duration_,
                           discard_padding_set_ ? discard_padding_ : 0);
  block_data_.reset();
  block_data_size_ = -1;
  block_duration_ = -1;
  block_add_id_ = -1;
  block_additional_data_.reset();
  block_additional_data_size_ = 0;
  discard_padding_ = -1;
  discard_padding_set_ = false;
  return result;
}

bool WebMClusterParser::OnUInt(int id, int64_t val) {
  int64_t* dst;
  switch (id) {
    case kWebMIdTimecode:
      dst = &cluster_timecode_;
      break;
    case kWebMIdBlockDuration:
      dst = &block_duration_;
      break;
    case kWebMIdBlockAddID:
      dst = &block_add_id_;
      break;
    default:
      return true;
  }
  if (*dst != -1)
    return false;
  *dst = val;
  return true;
}

bool WebMClusterParser::ParseBlock(bool is_simple_block,
                                   const uint8_t* buf,
                                   int size,
                                   const uint8_t* additional,
                                   int additional_size,
                                   int duration,
                                   int64_t discard_padding) {
  if (size < 4)
    return false;

  // Return an error if the trackNum > 127. We just aren't
  // going to support large track numbers right now.
  if (!(buf[0] & 0x80)) {
    LOG(ERROR) << "TrackNumber over 127 not supported";
    return false;
  }

  int track_num = buf[0] & 0x7f;
  int timecode = buf[1] << 8 | buf[2];
  int flags = buf[3] & 0xff;
  int lacing = (flags >> 1) & 0x3;

  if (lacing) {
    LOG(ERROR) << "Lacing " << lacing << " is not supported yet.";
    return false;
  }

  // Sign extend negative timecode offsets.
  if (timecode & 0x8000)
    timecode |= ~0xffff;

  const uint8_t* frame_data = buf + 4;
  int frame_size = size - (frame_data - buf);
  return OnBlock(is_simple_block, track_num, timecode, duration, flags,
                 frame_data, frame_size, additional, additional_size,
                 discard_padding);
}

bool WebMClusterParser::OnBinary(int id, const uint8_t* data, int size) {
  switch (id) {
    case kWebMIdSimpleBlock:
      return ParseBlock(true, data, size, NULL, 0, -1, 0);

    case kWebMIdBlock:
      if (block_data_) {
        LOG(ERROR) << "More than 1 Block in a BlockGroup is not "
                      "supported.";
        return false;
      }
      block_data_.reset(new uint8_t[size]);
      memcpy(block_data_.get(), data, size);
      block_data_size_ = size;
      return true;

    case kWebMIdBlockAdditional: {
      uint64_t block_add_id = base::HostToNet64(block_add_id_);
      if (block_additional_data_) {
        // TODO: Technically, more than 1 BlockAdditional is allowed as per
        // matroska spec. But for now we don't have a use case to support
        // parsing of such files. Take a look at this again when such a case
        // arises.
        LOG(ERROR) << "More than 1 BlockAdditional in a "
                      "BlockGroup is not supported.";
        return false;
      }
      // First 8 bytes of side_data in DecoderBuffer is the BlockAddID
      // element's value in Big Endian format. This is done to mimic ffmpeg
      // demuxer's behavior.
      block_additional_data_size_ = size + sizeof(block_add_id);
      block_additional_data_.reset(new uint8_t[block_additional_data_size_]);
      memcpy(block_additional_data_.get(), &block_add_id,
             sizeof(block_add_id));
      memcpy(block_additional_data_.get() + 8, data, size);
      return true;
    }
    case kWebMIdDiscardPadding: {
      if (discard_padding_set_ || size <= 0 || size > 8)
        return false;
      discard_padding_set_ = true;

      // Read in the big-endian integer.
      discard_padding_ = static_cast<int8_t>(data[0]);
      for (int i = 1; i < size; ++i)
        discard_padding_ = (discard_padding_ << 8) | data[i];

      return true;
    }
    default:
      return true;
  }
}

bool WebMClusterParser::OnBlock(bool is_simple_block,
                                int track_num,
                                int timecode,
                                int block_duration,
                                int flags,
                                const uint8_t* data,
                                int size,
                                const uint8_t* additional,
                                int additional_size,
                                int64_t discard_padding) {
  DCHECK_GE(size, 0);
  if (cluster_timecode_ == -1) {
    LOG(ERROR) << "Got a block before cluster timecode.";
    return false;
  }

  // TODO: Should relative negative timecode offsets be rejected?  Or only when
  // the absolute timecode is negative?  See http://crbug.com/271794
  if (timecode < 0) {
    LOG(ERROR) << "Got a block with negative timecode offset " << timecode;
    return false;
  }

  if (last_block_timecode_ != -1 && timecode < last_block_timecode_) {
    LOG(ERROR) << "Got a block with a timecode before the previous block.";
    return false;
  }

  Track* track = NULL;
  StreamType stream_type = kStreamAudio;
  std::string encryption_key_id;
  int64_t encoded_duration = kNoTimestamp;
  if (track_num == audio_.track_num()) {
    track = &audio_;
    encryption_key_id = audio_encryption_key_id_;
    if (encryption_key_id.empty()) {
      encoded_duration = TryGetEncodedAudioDuration(data, size);
    }
  } else if (track_num == video_.track_num()) {
    track = &video_;
    encryption_key_id = video_encryption_key_id_;
    stream_type = kStreamVideo;
  } else if (ignored_tracks_.find(track_num) != ignored_tracks_.end()) {
    return true;
  } else if (Track* const text_track = FindTextTrack(track_num)) {
    if (is_simple_block)  // BlockGroup is required for WebVTT cues
      return false;
    if (block_duration < 0)  // not specified
      return false;
    track = text_track;
    stream_type = kStreamText;
  } else {
    LOG(ERROR) << "Unexpected track number " << track_num;
    return false;
  }

  last_block_timecode_ = timecode;

  int64_t timestamp = (cluster_timecode_ + timecode) * timecode_multiplier_;

  scoped_refptr<MediaSample> buffer;
  if (stream_type != kStreamText) {
    // The first bit of the flags is set when a SimpleBlock contains only
    // keyframes. If this is a Block, then inspection of the payload is
    // necessary to determine whether it contains a keyframe or not.
    // http://www.matroska.org/technical/specs/index.html
    bool is_keyframe =
        is_simple_block ? (flags & 0x80) != 0 : track->IsKeyframe(data, size);

    // Every encrypted Block has a signal byte and IV prepended to it. Current
    // encrypted WebM request for comments specification is here
    // http://wiki.webmproject.org/encryption/webm-encryption-rfc
    scoped_ptr<DecryptConfig> decrypt_config;
    int data_offset = 0;
    if (!encryption_key_id.empty() &&
        !WebMCreateDecryptConfig(
             data, size,
             reinterpret_cast<const uint8_t*>(encryption_key_id.data()),
             encryption_key_id.size(),
             &decrypt_config, &data_offset)) {
      return false;
    }

    buffer = MediaSample::CopyFrom(data + data_offset, size - data_offset,
                                   additional, additional_size, is_keyframe);

    if (decrypt_config) {
      // TODO(kqyang): Decrypt it if it is encrypted.
      buffer->set_is_encrypted(true);
    }
  } else {
    std::string id, settings, content;
    WebMWebVTTParser::Parse(data, size, &id, &settings, &content);

    std::vector<uint8_t> side_data;
    MakeSideData(id.begin(), id.end(),
                 settings.begin(), settings.end(),
                 &side_data);

    buffer = MediaSample::CopyFrom(
        reinterpret_cast<const uint8_t*>(content.data()), content.length(),
        &side_data[0], side_data.size(), true);
  }

  buffer->set_pts(timestamp);
  if (cluster_start_time_ == kNoTimestamp)
    cluster_start_time_ = timestamp;

  int64_t block_duration_time_delta = kNoTimestamp;
  if (block_duration >= 0) {
    block_duration_time_delta = block_duration * timecode_multiplier_;
  }

  // Prefer encoded duration over BlockGroup->BlockDuration or
  // TrackEntry->DefaultDuration when available. This layering violation is a
  // workaround for http://crbug.com/396634, decreasing the likelihood of
  // fall-back to rough estimation techniques for Blocks that lack a
  // BlockDuration at the end of a cluster. Cross cluster durations are not
  // feasible given flexibility of cluster ordering and MSE APIs. Duration
  // estimation may still apply in cases of encryption and codecs for which
  // we do not extract encoded duration. Within a cluster, estimates are applied
  // as Block Timecode deltas, or once the whole cluster is parsed in the case
  // of the last Block in the cluster. See Track::EmitBuffer and
  // ApplyDurationEstimateIfNeeded().
  if (encoded_duration != kNoTimestamp) {
    DCHECK(encoded_duration != kInfiniteDuration);
    DCHECK(encoded_duration > 0);
    buffer->set_duration(encoded_duration);

    DVLOG(3) << __FUNCTION__ << " : "
             << "Using encoded duration " << encoded_duration;

    if (block_duration_time_delta != kNoTimestamp) {
      int64_t duration_difference =
          block_duration_time_delta - encoded_duration;

      const auto kWarnDurationDiff = timecode_multiplier_ * 2;
      if (duration_difference > kWarnDurationDiff) {
        LIMITED_DLOG(INFO, num_duration_errors_, kMaxDurationErrorLogs)
            << "BlockDuration (" << block_duration_time_delta
            << "ms) differs significantly from encoded duration ("
            << encoded_duration << "ms).";
      }
    }
  } else if (block_duration_time_delta != kNoTimestamp) {
    buffer->set_duration(block_duration_time_delta);
  } else {
    buffer->set_duration(track->default_duration());
  }

  return track->EmitBuffer(buffer);
}

WebMClusterParser::Track::Track(int track_num,
                                bool is_video,
                                int64_t default_duration,
                                const MediaParser::NewSampleCB& new_sample_cb)
    : track_num_(track_num),
      is_video_(is_video),
      default_duration_(default_duration),
      estimated_next_frame_duration_(kNoTimestamp),
      new_sample_cb_(new_sample_cb) {
  DCHECK(default_duration_ == kNoTimestamp || default_duration_ > 0);
}

WebMClusterParser::Track::~Track() {}

bool WebMClusterParser::Track::EmitBuffer(
    const scoped_refptr<MediaSample>& buffer) {
  DVLOG(2) << "EmitBuffer() : " << track_num_
           << " ts " << buffer->pts()
           << " dur " << buffer->duration()
           << " kf " << buffer->is_key_frame()
           << " size " << buffer->data_size();

  if (last_added_buffer_missing_duration_.get()) {
    int64_t derived_duration =
        buffer->pts() - last_added_buffer_missing_duration_->pts();
    last_added_buffer_missing_duration_->set_duration(derived_duration);

    DVLOG(2) << "EmitBuffer() : applied derived duration to held-back buffer : "
             << " ts "
             << last_added_buffer_missing_duration_->pts()
             << " dur "
             << last_added_buffer_missing_duration_->duration()
             << " kf " << last_added_buffer_missing_duration_->is_key_frame()
             << " size " << last_added_buffer_missing_duration_->data_size();
    scoped_refptr<MediaSample> updated_buffer =
        last_added_buffer_missing_duration_;
    last_added_buffer_missing_duration_ = NULL;
    if (!EmitBufferHelp(updated_buffer))
      return false;
  }

  if (buffer->duration() == kNoTimestamp) {
    last_added_buffer_missing_duration_ = buffer;
    DVLOG(2) << "EmitBuffer() : holding back buffer that is missing duration";
    return true;
  }

  return EmitBufferHelp(buffer);
}

void WebMClusterParser::Track::ApplyDurationEstimateIfNeeded() {
  if (!last_added_buffer_missing_duration_.get())
    return;

  int64_t estimated_duration = GetDurationEstimate();
  last_added_buffer_missing_duration_->set_duration(estimated_duration);

  if (is_video_) {
    // Exposing estimation so splicing/overlap frame processing can make
    // informed decisions downstream.
    // TODO(kqyang): Should we wait for the next cluster to set the duration?
    // last_added_buffer_missing_duration_->set_is_duration_estimated(true);
  }

  LIMITED_LOG(INFO, num_duration_estimates_, kMaxDurationEstimateLogs)
      << "Estimating WebM block duration to be "
      << estimated_duration
      << "ms for the last (Simple)Block in the Cluster for this Track. Use "
         "BlockGroups with BlockDurations at the end of each Track in a "
         "Cluster to avoid estimation.";

  DVLOG(2) << __FUNCTION__ << " new dur : ts "
           << last_added_buffer_missing_duration_->pts()
           << " dur "
           << last_added_buffer_missing_duration_->duration()
           << " kf " << last_added_buffer_missing_duration_->is_key_frame()
           << " size " << last_added_buffer_missing_duration_->data_size();

  // Don't use the applied duration as a future estimation (don't use
  // EmitBufferHelp() here.)
  new_sample_cb_.Run(track_num_, last_added_buffer_missing_duration_);
  last_added_buffer_missing_duration_ = NULL;
}

void WebMClusterParser::Track::Reset() {
  last_added_buffer_missing_duration_ = NULL;
}

bool WebMClusterParser::Track::IsKeyframe(const uint8_t* data, int size) const {
  // For now, assume that all blocks are keyframes for datatypes other than
  // video. This is a valid assumption for Vorbis, WebVTT, & Opus.
  if (!is_video_)
    return true;

  // Make sure the block is big enough for the minimal keyframe header size.
  if (size < 7)
    return false;

  // The LSb of the first byte must be a 0 for a keyframe.
  // http://tools.ietf.org/html/rfc6386 Section 19.1
  if ((data[0] & 0x01) != 0)
    return false;

  // Verify VP8 keyframe startcode.
  // http://tools.ietf.org/html/rfc6386 Section 19.1
  if (data[3] != 0x9d || data[4] != 0x01 || data[5] != 0x2a)
    return false;

  return true;
}

bool WebMClusterParser::Track::EmitBufferHelp(
    const scoped_refptr<MediaSample>& buffer) {
  DCHECK(!last_added_buffer_missing_duration_.get());

  int64_t duration = buffer->duration();
  if (duration < 0 || duration == kNoTimestamp) {
    LOG(ERROR) << "Invalid buffer duration: " << duration;
    return false;
  }

  // The estimated frame duration is the minimum (for audio) or the maximum
  // (for video) non-zero duration since the last initialization segment. The
  // minimum is used for audio to ensure frame durations aren't overestimated,
  // triggering unnecessary frame splicing. For video, splicing does not apply,
  // so maximum is used and overlap is simply resolved by showing the
  // later of the overlapping frames at its given PTS, effectively trimming down
  // the over-estimated duration of the previous frame.
  // TODO: Use max for audio and disable splicing whenever estimated buffers are
  // encountered.
  if (duration > 0) {
    int64_t orig_duration_estimate = estimated_next_frame_duration_;
    if (estimated_next_frame_duration_ == kNoTimestamp) {
      estimated_next_frame_duration_ = duration;
    } else if (is_video_) {
      estimated_next_frame_duration_ =
          std::max(duration, estimated_next_frame_duration_);
    } else {
      estimated_next_frame_duration_ =
          std::min(duration, estimated_next_frame_duration_);
    }

    if (orig_duration_estimate != estimated_next_frame_duration_) {
      DVLOG(3) << "Updated duration estimate:"
               << orig_duration_estimate
               << " -> "
               << estimated_next_frame_duration_
               << " at timestamp: "
               << buffer->dts();
    }
  }

  new_sample_cb_.Run(track_num_, buffer);
  return true;
}

int64_t WebMClusterParser::Track::GetDurationEstimate() {
  int64_t duration = estimated_next_frame_duration_;
  if (duration != kNoTimestamp) {
    DVLOG(3) << __FUNCTION__ << " : using estimated duration";
  } else {
    DVLOG(3) << __FUNCTION__ << " : using hardcoded default duration";
    if (is_video_) {
      duration = kDefaultVideoBufferDurationInMs * kMicrosecondsPerMillisecond;
    } else {
      duration = kDefaultAudioBufferDurationInMs * kMicrosecondsPerMillisecond;
    }
  }

  DCHECK(duration > 0);
  DCHECK(duration != kNoTimestamp);
  return duration;
}

void WebMClusterParser::ResetTextTracks() {
  for (TextTrackMap::iterator it = text_track_map_.begin();
       it != text_track_map_.end();
       ++it) {
    it->second.Reset();
  }
}

WebMClusterParser::Track*
WebMClusterParser::FindTextTrack(int track_num) {
  const TextTrackMap::iterator it = text_track_map_.find(track_num);

  if (it == text_track_map_.end())
    return NULL;

  return &it->second;
}

}  // namespace media
}  // namespace edash_packager