shaka-player/lib/media/segment_index.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.media.SegmentIndex');

goog.require('goog.asserts');
goog.require('shaka.log');
goog.require('shaka.media.SegmentReference');
goog.require('shaka.util.IDestroyable');


/**
 * SegmentIndex.
 *
 * @implements {shaka.util.IDestroyable}
 * @export
 */
shaka.media.SegmentIndex = class {
  /**
   * @param {!Array.<!shaka.media.SegmentReference>} references The list of
   *   SegmentReferences, which must be sorted first by their start times
   *   (ascending) and second by their end times (ascending).  They must have
   *   continuous, increasing positions.
   */
  constructor(references) {
    if (goog.DEBUG) {
      shaka.media.SegmentIndex.assertCorrectReferences_(references);
    }

    /** @private {Array.<!shaka.media.SegmentReference>} */
    this.references_ = references;
  }


  /**
   * @override
   * @export
   */
  destroy() {
    this.references_ = null;
    return Promise.resolve();
  }


  /**
   * Finds the position of the segment for the given time, in seconds, relative
   * to the start of a particular Period.  Returns the position of the segment
   * with the largest end time if more than one segment is known for the given
   * time.
   *
   * @param {number} time
   * @return {?number} The position of the segment, or null
   *   if the position of the segment could not be determined.
   * @export
   */
  find(time) {
    // For live streams, searching from the end is faster.  For VOD, it balances
    // out either way.  In both cases, references_.length is small enough that
    // the difference isn't huge.
    for (let i = this.references_.length - 1; i >= 0; --i) {
      const r = this.references_[i];
      // Note that a segment ends immediately before the end time.
      if ((time >= r.startTime) && (time < r.endTime)) {
        return r.position;
      }
    }
    if (this.references_.length && time < this.references_[0].startTime) {
      return this.references_[0].position;
    }

    return null;
  }


  /**
   * Gets the SegmentReference for the segment at the given position.
   *
   * @param {number} position The position of the segment.
   * @return {shaka.media.SegmentReference} The SegmentReference, or null if
   *   no such SegmentReference exists.
   * @export
   */
  get(position) {
    if (this.references_.length == 0) {
      return null;
    }

    const index = position - this.references_[0].position;
    if (index < 0 || index >= this.references_.length) {
      return null;
    }

    return this.references_[index];
  }


  /**
   * Offset all segment references by a fixed amount.
   *
   * @param {number} offset The amount to add to each segment's start and end
   *   times.
   * @export
   */
  offset(offset) {
    for (let i = 0; i < this.references_.length; ++i) {
      this.references_[i].startTime += offset;
      this.references_[i].endTime += offset;
    }
  }


  /**
   * Merges the given SegmentReferences.  Supports extending the original
   * references only.  Will not replace old references or interleave new ones.
   *
   * @param {!Array.<!shaka.media.SegmentReference>} references The list of
   *   SegmentReferences, which must be sorted first by their start times
   *   (ascending) and second by their end times (ascending).  They must have
   *   continuous, increasing positions.
   * @export
   */
  merge(references) {
    if (goog.DEBUG) {
      shaka.media.SegmentIndex.assertCorrectReferences_(references);
    }

    let newReferences = [];
    let i = 0;
    let j = 0;

    while ((i < this.references_.length) && (j < references.length)) {
      const r1 = this.references_[i];
      const r2 = references[j];

      if (r1.startTime < r2.startTime) {
        newReferences.push(r1);
        i++;
      } else if (r1.startTime > r2.startTime) {
        if (i == 0) {
          // If the reference appears before any existing reference, it may have
          // been evicted before; in this case, simply add it back and it will
          // be evicted again later.
          newReferences.push(r2);
        } else {
          // Drop the new reference if it would have to be interleaved with the
          // old one.  Issue a warning, since this is not a supported update.
          shaka.log.warning(
              'Refusing to rewrite original references on update!');
        }
        j++;
      } else {
        // When period is changed, fit() will expand the last segment to the
        // start of the next period.  So, it is valid to have end time updated
        // to the last segment reference in a period.
        if (Math.abs(r1.endTime - r2.endTime) > 0.1) {
          goog.asserts.assert(r2.endTime > r1.endTime &&
              i == this.references_.length - 1 &&
              j == references.length - 1,
          'This should be an update of the last segment in a period');
          const r = new shaka.media.SegmentReference(r1.position,
              r2.startTime, r2.endTime, r2.getUris, r2.startByte, r2.endByte);
          newReferences.push(r);
        } else {
          // Drop the new reference if there's an old reference with the
          // same time.
          newReferences.push(r1);
        }
        i++;
        j++;
      }
    }

    while (i < this.references_.length) {
      newReferences.push(this.references_[i++]);
    }

    if (newReferences.length) {
      // The rest of these references may need to be renumbered.
      let nextPosition = newReferences[newReferences.length - 1].position + 1;
      while (j < references.length) {
        const r = references[j++];
        const r2 = new shaka.media.SegmentReference(nextPosition++,
            r.startTime, r.endTime, r.getUris, r.startByte, r.endByte);
        newReferences.push(r2);
      }
    } else {
      newReferences = references;
    }

    if (goog.DEBUG) {
      shaka.media.SegmentIndex.assertCorrectReferences_(newReferences);
    }

    this.references_ = newReferences;
  }


  /**
   * Replace existing references with new ones, without merging.
   *
   * @param {!Array.<!shaka.media.SegmentReference>} newReferences
   */
  replace(newReferences) {
    if (goog.DEBUG) {
      shaka.media.SegmentIndex.assertCorrectReferences_(newReferences);
    }
    this.references_ = newReferences;
  }


  /**
   * Removes all SegmentReferences that end before the given time.
   *
   * @param {number} time The time in seconds.
   * @export
   */
  evict(time) {
    for (let i = 0; i < this.references_.length; ++i) {
      if (this.references_[i].endTime > time) {
        this.references_.splice(0, i);
        return;
      }
    }
    this.references_ = [];
  }


  /**
   * Expands the first SegmentReference so it begins at the start of its Period
   * if it already begins close to the start of its Period.
   *
   * Also expands or contracts the last SegmentReference so it ends at the end
   * of its Period.
   *
   * Do not call on the last period of a live presentation (unknown duration).
   * It is okay to call on the other periods of a live presentation, where the
   * duration is known and another period has been added.
   *
   * @param {?number} periodDuration
   */
  fit(periodDuration) {
    goog.asserts.assert(periodDuration != null,
        'Period duration must be known for static content!');
    goog.asserts.assert(periodDuration != Infinity,
        'Period duration must be finite for static content!');

    // Trim out references we will never use.
    while (this.references_.length) {
      const lastReference = this.references_[this.references_.length - 1];
      if (lastReference.startTime >= periodDuration) {
        this.references_.pop();
      } else {
        break;
      }
    }
    while (this.references_.length) {
      const firstReference = this.references_[0];
      if (firstReference.endTime <= 0) {
        this.references_.shift();
      } else {
        break;
      }
    }

    if (this.references_.length == 0) {
      return;
    }

    // Adjust the last SegmentReference.
    const lastReference = this.references_[this.references_.length - 1];
    this.references_[this.references_.length - 1] =
        new shaka.media.SegmentReference(
            lastReference.position,
            lastReference.startTime,
            /* endTime */ periodDuration,
            lastReference.getUris,
            lastReference.startByte,
            lastReference.endByte);
  }
};


if (goog.DEBUG) {
  /**
   * Asserts that the given SegmentReferences are sorted and have continuous,
   * increasing positions.
   *
   * @param {!Array.<shaka.media.SegmentReference>} references
   * @private
   */
  shaka.media.SegmentIndex.assertCorrectReferences_ = (references) => {
    goog.asserts.assert(references.every((r2, i) => {
      if (i == 0) {
        return true;
      }
      const r1 = references[i - 1];
      if (r2.position != r1.position + 1) {
        return false;
      }
      if (r1.startTime < r2.startTime) {
        return true;
      } else if (r1.startTime > r2.startTime) {
        return false;
      } else {
        if (r1.endTime <= r2.endTime) {
          return true;
        } else {
          return false;
        }
      }
    }), 'SegmentReferences are incorrect');
  };
}