shaka-player/lib/text/text_engine.js

/**
 * @license
 * Copyright 2016 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

goog.provide('shaka.text.TextEngine');

goog.require('goog.asserts');
goog.require('shaka.text.Cue');
goog.require('shaka.util.Error');
goog.require('shaka.util.IDestroyable');
goog.require('shaka.util.MimeUtils');


/**
 * Manages text parsers and cues.
 *
 * @param {shaka.extern.TextDisplayer} displayer
 * @struct
 * @constructor
 * @implements {shaka.util.IDestroyable}
 */
shaka.text.TextEngine = function(displayer) {
  /** @private {shaka.extern.TextParser} */
  this.parser_ = null;

  /** @private {shaka.extern.TextDisplayer} */
  this.displayer_ = displayer;

  /** @private {number} */
  this.timestampOffset_ = 0;

  /** @private {number} */
  this.appendWindowStart_ = 0;

  /** @private {number} */
  this.appendWindowEnd_ = Infinity;

  /** @private {?number} */
  this.bufferStart_ = null;

  /** @private {?number} */
  this.bufferEnd_ = null;

  /** @private {string} */
  this.selectedClosedCaptionId_ = '';

  /**
   * The closed captions map stores the CEA closed captions by closed captions
   * id and start and end time.
   * It's used as the buffer of closed caption text streams, to show captions
   * when we start displaying captions or switch caption tracks, we need to be
   * able to get the cues for the other language and display them without
   * re-fetching the video segments they were embedded in.
   * Structure of closed caption map:
   * closed caption id -> {start and end time -> cues}
   * @private {!Map.<string, !Map.<string, !Array.<shaka.text.Cue>>>} */
  this.closedCaptionsMap_ = new Map();
};


/** @private {!Object.<string, !shaka.extern.TextParserPlugin>} */
shaka.text.TextEngine.parserMap_ = {};


/**
 * @param {string} mimeType
 * @param {!shaka.extern.TextParserPlugin} plugin
 * @export
 */
shaka.text.TextEngine.registerParser = function(mimeType, plugin) {
  shaka.text.TextEngine.parserMap_[mimeType] = plugin;
};


/**
 * @param {string} mimeType
 * @export
 */
shaka.text.TextEngine.unregisterParser = function(mimeType) {
  delete shaka.text.TextEngine.parserMap_[mimeType];
};


/**
 * @param {string} mimeType
 * @return {boolean}
 */
shaka.text.TextEngine.isTypeSupported = function(mimeType) {
  if (shaka.text.TextEngine.parserMap_[mimeType]) {
    // An actual parser is available.
    return true;
  }
  if (window.muxjs &&
      mimeType == shaka.util.MimeUtils.CLOSED_CAPTION_MIMETYPE) {
    // Will be handled by mux.js.
    return true;
  }
  return false;
};


/** @override */
shaka.text.TextEngine.prototype.destroy = function() {
  this.parser_ = null;
  this.displayer_ = null;
  this.closedCaptionsMap_.clear();

  return Promise.resolve();
};


/**
 * Initialize the parser.  This can be called multiple times, but must be called
 * at least once before appendBuffer.
 *
 * @param {string} mimeType
 */
shaka.text.TextEngine.prototype.initParser = function(mimeType) {
  // No parser for CEA, which is extracted from video and side-loaded
  // into TextEngine and TextDisplayer.
  if (mimeType == shaka.util.MimeUtils.CLOSED_CAPTION_MIMETYPE) {
    return;
  }

  const Factory = shaka.text.TextEngine.parserMap_[mimeType];
  goog.asserts.assert(
      Factory,
      'Text type negotiation should have happened already');
  this.parser_ = new Factory();
};


/**
 * Parse the start time from the text media segment, if possible.
 *
 * @param {!ArrayBuffer} buffer
 * @return {number}
 * @throws {shaka.util.Error} on failure
 */
shaka.text.TextEngine.prototype.getStartTime = function(buffer) {
  goog.asserts.assert(this.parser_, 'The parser should already be initialized');

  /** @type {shaka.extern.TextParser.TimeContext} **/
  const time = {
    periodStart: 0,
    segmentStart: null,
    segmentEnd: 0,
  };

  // Parse the buffer and extract the first cue start time.
  try {
    const allCues = this.parser_.parseMedia(new Uint8Array(buffer), time);
    return allCues[0].startTime;
  } catch (exception) {
    // This could be a failure from the parser itself (init segment required)
    // or an exception from allCues.length being zero.
    throw new shaka.util.Error(
        shaka.util.Error.Severity.CRITICAL,
        shaka.util.Error.Category.TEXT,
        shaka.util.Error.Code.UNABLE_TO_EXTRACT_CUE_START_TIME,
        exception);
  }
};


/**
 * @param {!ArrayBuffer} buffer
 * @param {?number} startTime relative to the start of the presentation
 * @param {?number} endTime relative to the start of the presentation
 * @return {!Promise}
 */
shaka.text.TextEngine.prototype.appendBuffer =
    function(buffer, startTime, endTime) {
  goog.asserts.assert(this.parser_, 'The parser should already be initialized');

  // Start the operation asynchronously to avoid blocking the caller.
  return Promise.resolve().then(() => {
    // Check that TextEngine hasn't been destroyed.
    if (!this.parser_ || !this.displayer_) return;

    if (startTime == null || endTime == null) {
      this.parser_.parseInit(new Uint8Array(buffer));
      return;
    }

    /** @type {shaka.extern.TextParser.TimeContext} **/
    const time = {
      periodStart: this.timestampOffset_,
      segmentStart: startTime,
      segmentEnd: endTime,
    };

    // Parse the buffer and add the new cues.
    const allCues = this.parser_.parseMedia(new Uint8Array(buffer), time);
    const cuesToAppend = allCues.filter((cue) => {
      return cue.startTime >= this.appendWindowStart_ &&
             cue.startTime < this.appendWindowEnd_;
    });

    this.displayer_.append(cuesToAppend);

    // NOTE: We update the buffered range from the start and end times passed
    // down from the segment reference, not with the start and end times of the
    // parsed cues.  This is important because some segments may contain no
    // cues, but we must still consider those ranges buffered.
    if (this.bufferStart_ == null) {
      this.bufferStart_ = Math.max(startTime, this.appendWindowStart_);
    } else {
      // We already had something in buffer, and we assume we are extending the
      // range from the end.
      goog.asserts.assert(this.bufferEnd_ != null,
                          'There should already be a buffered range end.');
      goog.asserts.assert((startTime - this.bufferEnd_) <= 1,
                          'There should not be a gap in text references >1s');
    }
    this.bufferEnd_ = Math.min(endTime, this.appendWindowEnd_);
  });
};


/**
 * @param {number} startTime relative to the start of the presentation
 * @param {number} endTime relative to the start of the presentation
 * @return {!Promise}
 */
shaka.text.TextEngine.prototype.remove = function(startTime, endTime) {
  // Start the operation asynchronously to avoid blocking the caller.
  return Promise.resolve().then(() => {
    if (this.displayer_ && this.displayer_.remove(startTime, endTime)) {
      if (this.bufferStart_ == null) {
        goog.asserts.assert(this.bufferEnd_ == null,
                            'end must be null if startTime is null');
      } else {
        goog.asserts.assert(this.bufferEnd_ != null,
                            'end must be non-null if startTime is non-null');

        // Update buffered range.
        if (endTime <= this.bufferStart_ || startTime >= this.bufferEnd_) {
          // No intersection.  Nothing was removed.
        } else if (startTime <= this.bufferStart_ &&
                   endTime >= this.bufferEnd_) {
          // We wiped out everything.
          this.bufferStart_ = this.bufferEnd_ = null;
        } else if (startTime <= this.bufferStart_ &&
                   endTime < this.bufferEnd_) {
          // We removed from the beginning of the range.
          this.bufferStart_ = endTime;
        } else if (startTime > this.bufferStart_ &&
                   endTime >= this.bufferEnd_) {
          // We removed from the end of the range.
          this.bufferEnd_ = startTime;
        } else {
          // We removed from the middle?  StreamingEngine isn't supposed to.
          goog.asserts.assert(
              false, 'removal from the middle is not supported by TextEngine');
        }
      }
    }
  });
};


/** @param {number} timestampOffset */
shaka.text.TextEngine.prototype.setTimestampOffset =
    function(timestampOffset) {
  this.timestampOffset_ = timestampOffset;
};


/**
 * @param {number} appendWindowStart
 * @param {number} appendWindowEnd
 */
shaka.text.TextEngine.prototype.setAppendWindow =
    function(appendWindowStart, appendWindowEnd) {
  this.appendWindowStart_ = appendWindowStart;
  this.appendWindowEnd_ = appendWindowEnd;
};


/**
 * @return {?number} Time in seconds of the beginning of the buffered range,
 *   or null if nothing is buffered.
 */
shaka.text.TextEngine.prototype.bufferStart = function() {
  return this.bufferStart_;
};


/**
 * @return {?number} Time in seconds of the end of the buffered range,
 *   or null if nothing is buffered.
 */
shaka.text.TextEngine.prototype.bufferEnd = function() {
  return this.bufferEnd_;
};


/**
 * @param {number} t A timestamp
 * @return {boolean}
 */
shaka.text.TextEngine.prototype.isBuffered = function(t) {
  if (this.bufferStart_ == null || this.bufferEnd_ == null) {
    return false;
  }
  return t >= this.bufferStart_ && t < this.bufferEnd_;
};


/**
 * @param {number} t A timestamp
 * @return {number} Number of seconds ahead of 't' we have buffered
 */
shaka.text.TextEngine.prototype.bufferedAheadOf = function(t) {
  if (this.bufferEnd_ == null || this.bufferEnd_ < t) return 0;

  goog.asserts.assert(
      this.bufferStart_ != null, 'start should not be null if end is not null');

  return this.bufferEnd_ - Math.max(t, this.bufferStart_);
};


/**
 * Append cues to text displayer.
 *
 * @param {!Array.<!shaka.text.Cue>} cues
 * @export
 */
shaka.text.TextEngine.prototype.appendCues = function(cues) {
  this.displayer_.append(cues);
};


/**
 * Set the selected closed captions id.
 * Append the cues stored in the closed captions map until buffer end time.
 * This is to fill the gap between buffered and unbuffered captions, and to
 * avoid duplicates that would be caused by any future video segments parsed for
 * captions.
 *
 * @param {string} id
 * @param {number} bufferEndTime Load any stored cues up to this time.
 * @export
 */
shaka.text.TextEngine.prototype.setSelectedClosedCaptionId =
    function(id, bufferEndTime) {
  this.selectedClosedCaptionId_ = id;

  const captionsMap = this.closedCaptionsMap_.get(id);
  if (captionsMap) {
    for (const startAndEndTime of captionsMap.keys()) {
      /** @type {Array.<!shaka.text.Cue>} */
      let cues = captionsMap.get(startAndEndTime);
      if (cues) {
        cues = cues.filter((c) => c.endTime <= bufferEndTime);
        this.displayer_.append(cues);
      }
    }
  }
};


/**
 * Store the closed captions in the text engine, and append the cues to the text
 * displayer.  This is a side-channel used for embedded text only.
 *
 * @param {!Array.<muxjs.mp4.ClosedCaption>} closedCaptions
 * @param {?number} startTime relative to the start of the presentation
 * @param {?number} endTime relative to the start of the presentation
 * @param {number} videoTimestampOffset the timestamp offset of the video
 *   stream in which these captions were embedded
 */
shaka.text.TextEngine.prototype.storeAndAppendClosedCaptions = function(
    closedCaptions, startTime, endTime, videoTimestampOffset) {
  const startAndEndTime = startTime + ' ' + endTime;
  const captionsMap = new Map();

  for (const caption of closedCaptions) {
    const id = caption.stream;
    if (!captionsMap.has(id)) {
      captionsMap.set(id, new Map());
    }
    if (!captionsMap.get(id).has(startAndEndTime)) {
      captionsMap.get(id).set(startAndEndTime, []);
    }

    // Adjust CEA captions with respect to the timestamp offset of the video
    // stream in which they were embedded.
    caption.startTime += videoTimestampOffset;
    caption.endTime += videoTimestampOffset;

    const keepThisCue =
        caption.startTime >= this.appendWindowStart_ &&
        caption.startTime < this.appendWindowEnd_;
    if (!keepThisCue) {
      continue;
    }
    /** @type {!shaka.text.Cue} */
    const cue = new shaka.text.Cue(
        caption.startTime, caption.endTime, caption.text);
    captionsMap.get(id).get(startAndEndTime).push(cue);
    if (id == this.selectedClosedCaptionId_) {
      this.displayer_.append([cue]);
    }
  }

  for (const id of captionsMap.keys()) {
    if (!this.closedCaptionsMap_.has(id)) {
      this.closedCaptionsMap_.set(id, new Map());
    }
    for (const startAndEndTime of captionsMap.get(id).keys()) {
      const cues = captionsMap.get(id).get(startAndEndTime);
      this.closedCaptionsMap_.get(id).set(startAndEndTime, cues);
    }
  }

  if (this.bufferStart_ == null) {
    this.bufferStart_ = Math.max(startTime, this.appendWindowStart_);
  } else {
    this.bufferStart_ = Math.min(
        this.bufferStart_, Math.max(startTime, this.appendWindowStart_));
  }

  this.bufferEnd_ = Math.max(
      this.bufferEnd_, Math.min(endTime, this.appendWindowEnd_));
};


/**
 * Get the number of closed caption channels.
 *
 * This function is for TESTING ONLY. DO NOT USE in the library.
 *
 * @return {number}
 */
shaka.text.TextEngine.prototype.getNumberOfClosedCaptionChannels = function() {
  return this.closedCaptionsMap_.size;
};

/**
 * Get the number of closed caption cues for a given channel. If there is
 * no channel for the given channel id, this will return 0.
 *
 * This function is for TESTING ONLY. DO NOT USE in the library.
 *
 * @param {string} channelId
 * @return {number}
 */
shaka.text.TextEngine.prototype.getNumberOfClosedCaptionsInChannel =
    function(channelId) {
  const channel = this.closedCaptionsMap_.get(channelId);
  return channel ? channel.size : 0;
};