fragment-tracker.js

import EventHandler from '../event-handler';
import Event from '../events';

export const FragmentState = {
  NOT_LOADED: 'NOT_LOADED',
  APPENDING: 'APPENDING',
  PARTIAL: 'PARTIAL',
  OK: 'OK'
};

export class FragmentTracker extends EventHandler {
  constructor (hls) {
    super(hls,
      Event.BUFFER_APPENDED,
      Event.FRAG_BUFFERED,
      Event.FRAG_LOADED
    );

    this.bufferPadding = 0.2;

    this.fragments = Object.create(null);
    this.timeRanges = Object.create(null);

    this.config = hls.config;
  }

  destroy () {
    this.fragments = null;
    this.timeRanges = null;
    this.config = null;
    EventHandler.prototype.destroy.call(this);
    super.destroy();
  }

  /**
   * Return a Fragment that match the position and levelType.
   * If not found any Fragment, return null
   * @param {number} position
   * @param {LevelType} levelType
   * @returns {Fragment|null}
   */
  getBufferedFrag (position, levelType) {
    const fragments = this.fragments;
    const bufferedFrags = Object.keys(fragments).filter(key => {
      const fragmentEntity = fragments[key];
      if (fragmentEntity.body.type !== levelType) {
        return false;
      }

      if (!fragmentEntity.buffered) {
        return false;
      }

      const frag = fragmentEntity.body;
      return frag.startPTS <= position && position <= frag.endPTS;
    });
    if (bufferedFrags.length === 0) {
      return null;
    } else {
      // https://github.com/video-dev/hls.js/pull/1545#discussion_r166229566
      const bufferedFragKey = bufferedFrags.pop();
      return fragments[bufferedFragKey].body;
    }
  }

  /**
   * Partial fragments effected by coded frame eviction will be removed
   * The browser will unload parts of the buffer to free up memory for new buffer data
   * Fragments will need to be reloaded when the buffer is freed up, removing partial fragments will allow them to reload(since there might be parts that are still playable)
   * @param {String} elementaryStream The elementaryStream of media this is (eg. video/audio)
   * @param {TimeRanges} timeRange TimeRange object from a sourceBuffer
   */
  detectEvictedFragments (elementaryStream, timeRange) {
    let fragmentTimes, time;
    // Check if any flagged fragments have been unloaded
    Object.keys(this.fragments).forEach(key => {
      const fragmentEntity = this.fragments[key];
      if (fragmentEntity.buffered === true) {
        const esData = fragmentEntity.range[elementaryStream];
        if (esData) {
          fragmentTimes = esData.time;
          for (let i = 0; i < fragmentTimes.length; i++) {
            time = fragmentTimes[i];

            if (this.isTimeBuffered(time.startPTS, time.endPTS, timeRange) === false) {
              // Unregister partial fragment as it needs to load again to be reused
              this.removeFragment(fragmentEntity.body);
              break;
            }
          }
        }
      }
    });
  }

  /**
   * Checks if the fragment passed in is loaded in the buffer properly
   * Partially loaded fragments will be registered as a partial fragment
   * @param {Object} fragment Check the fragment against all sourceBuffers loaded
   */
  detectPartialFragments (fragment) {
    let fragKey = this.getFragmentKey(fragment);
    let fragmentEntity = this.fragments[fragKey];
    if (fragmentEntity) {
      fragmentEntity.buffered = true;

      Object.keys(this.timeRanges).forEach(elementaryStream => {
        if (fragment.hasElementaryStream(elementaryStream)) {
          let timeRange = this.timeRanges[elementaryStream];
          // Check for malformed fragments
          // Gaps need to be calculated for each elementaryStream
          fragmentEntity.range[elementaryStream] = this.getBufferedTimes(fragment.startPTS, fragment.endPTS, timeRange);
        }
      });
    }
  }

  getBufferedTimes (startPTS, endPTS, timeRange) {
    let fragmentTimes = [];
    let startTime, endTime;
    let fragmentPartial = false;
    for (let i = 0; i < timeRange.length; i++) {
      startTime = timeRange.start(i) - this.bufferPadding;
      endTime = timeRange.end(i) + this.bufferPadding;
      if (startPTS >= startTime && endPTS <= endTime) {
        // Fragment is entirely contained in buffer
        // No need to check the other timeRange times since it's completely playable
        fragmentTimes.push({
          startPTS: Math.max(startPTS, timeRange.start(i)),
          endPTS: Math.min(endPTS, timeRange.end(i))
        });
        break;
      } else if (startPTS < endTime && endPTS > startTime) {
        // Check for intersection with buffer
        // Get playable sections of the fragment
        fragmentTimes.push({
          startPTS: Math.max(startPTS, timeRange.start(i)),
          endPTS: Math.min(endPTS, timeRange.end(i))
        });
        fragmentPartial = true;
      } else if (endPTS <= startTime) {
        // No need to check the rest of the timeRange as it is in order
        break;
      }
    }

    return {
      time: fragmentTimes,
      partial: fragmentPartial
    };
  }

  getFragmentKey (fragment) {
    return `${fragment.type}_${fragment.level}_${fragment.urlId}_${fragment.sn}`;
  }

  /**
   * Gets the partial fragment for a certain time
   * @param {Number} time
   * @returns {Object} fragment Returns a partial fragment at a time or null if there is no partial fragment
   */
  getPartialFragment (time) {
    let timePadding, startTime, endTime;
    let bestFragment = null;
    let bestOverlap = 0;
    Object.keys(this.fragments).forEach(key => {
      const fragmentEntity = this.fragments[key];
      if (this.isPartial(fragmentEntity)) {
        startTime = fragmentEntity.body.startPTS - this.bufferPadding;
        endTime = fragmentEntity.body.endPTS + this.bufferPadding;
        if (time >= startTime && time <= endTime) {
          // Use the fragment that has the most padding from start and end time
          timePadding = Math.min(time - startTime, endTime - time);
          if (bestOverlap <= timePadding) {
            bestFragment = fragmentEntity.body;
            bestOverlap = timePadding;
          }
        }
      }
    });
    return bestFragment;
  }

  /**
   * @param {Object} fragment The fragment to check
   * @returns {String} Returns the fragment state when a fragment never loaded or if it partially loaded
   */
  getState (fragment) {
    let fragKey = this.getFragmentKey(fragment);
    let fragmentEntity = this.fragments[fragKey];
    let state = FragmentState.NOT_LOADED;

    if (fragmentEntity !== undefined) {
      if (!fragmentEntity.buffered) {
        state = FragmentState.APPENDING;
      } else if (this.isPartial(fragmentEntity) === true) {
        state = FragmentState.PARTIAL;
      } else {
        state = FragmentState.OK;
      }
    }

    return state;
  }

  isPartial (fragmentEntity) {
    return fragmentEntity.buffered === true &&
      ((fragmentEntity.range.video !== undefined && fragmentEntity.range.video.partial === true) ||
        (fragmentEntity.range.audio !== undefined && fragmentEntity.range.audio.partial === true));
  }

  isTimeBuffered (startPTS, endPTS, timeRange) {
    let startTime, endTime;
    for (let i = 0; i < timeRange.length; i++) {
      startTime = timeRange.start(i) - this.bufferPadding;
      endTime = timeRange.end(i) + this.bufferPadding;
      if (startPTS >= startTime && endPTS <= endTime) {
        return true;
      }

      if (endPTS <= startTime) {
        // No need to check the rest of the timeRange as it is in order
        return false;
      }
    }

    return false;
  }

  /**
   * Fires when a fragment loading is completed
   */
  onFragLoaded (e) {
    const fragment = e.frag;
    // don't track initsegment (for which sn is not a number)
    // don't track frags used for bitrateTest, they're irrelevant.
    if (!Number.isFinite(fragment.sn) || fragment.bitrateTest) {
      return;
    }

    this.fragments[this.getFragmentKey(fragment)] = {
      body: fragment,
      range: Object.create(null),
      buffered: false
    };
  }

  /**
   * Fires when the buffer is updated
   */
  onBufferAppended (e) {
    // Store the latest timeRanges loaded in the buffer
    this.timeRanges = e.timeRanges;
    Object.keys(this.timeRanges).forEach(elementaryStream => {
      let timeRange = this.timeRanges[elementaryStream];
      this.detectEvictedFragments(elementaryStream, timeRange);
    });
  }

  /**
   * Fires after a fragment has been loaded into the source buffer
   */
  onFragBuffered (e) {
    this.detectPartialFragments(e.frag);
  }

  /**
   * Return true if fragment tracker has the fragment.
   * @param {Object} fragment
   * @returns {boolean}
   */
  hasFragment (fragment) {
    const fragKey = this.getFragmentKey(fragment);
    return this.fragments[fragKey] !== undefined;
  }

  /**
   * Remove a fragment from fragment tracker until it is loaded again
   * @param {Object} fragment The fragment to remove
   */
  removeFragment (fragment) {
    let fragKey = this.getFragmentKey(fragment);
    delete this.fragments[fragKey];
  }

  /**
   * Remove all fragments from fragment tracker.
   */
  removeAllFragments () {
    this.fragments = Object.create(null);
  }
}