shaka-player/lib/dash/mp4_segment_index_parser.js

/*! @license
 * Shaka Player
 * Copyright 2016 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

goog.provide('shaka.dash.Mp4SegmentIndexParser');

goog.require('goog.asserts');
goog.require('shaka.log');
goog.require('shaka.media.InitSegmentReference');
goog.require('shaka.media.SegmentReference');
goog.require('shaka.util.Error');
goog.require('shaka.util.Mp4Parser');


shaka.dash.Mp4SegmentIndexParser = class {
  /**
   * Parses SegmentReferences from an ISO BMFF SIDX structure.
   * @param {BufferSource} sidxData The MP4's container's SIDX.
   * @param {number} sidxOffset The SIDX's offset, in bytes, from the start of
   *   the MP4 container.
   * @param {!Array<string>} uris The possible locations of the MP4 file that
   *   contains the segments.
   * @param {shaka.media.InitSegmentReference} initSegmentReference
   * @param {number} timestampOffset
   * @param {number} appendWindowStart
   * @param {number} appendWindowEnd
   * @param {boolean=} indexIsExternal sidx files are external to the media
   * @return {!Array<!shaka.media.SegmentReference>}
   */
  static parse(
      sidxData, sidxOffset, uris, initSegmentReference, timestampOffset,
      appendWindowStart, appendWindowEnd, indexIsExternal) {
    const Mp4SegmentIndexParser = shaka.dash.Mp4SegmentIndexParser;

    /** @type {!Array<!shaka.media.SegmentReference>} */
    let references;

    const parser = new shaka.util.Mp4Parser()
        .fullBox('sidx', (box) => {
          references = Mp4SegmentIndexParser.parseSIDX_(
              sidxOffset,
              initSegmentReference,
              timestampOffset,
              appendWindowStart,
              appendWindowEnd,
              uris,
              box,
              indexIsExternal);
        });

    if (sidxData) {
      parser.parse(sidxData);
    }

    if (references) {
      return references;
    } else {
      shaka.log.error('Invalid box type, expected "sidx".');
      throw new shaka.util.Error(
          shaka.util.Error.Severity.CRITICAL,
          shaka.util.Error.Category.MEDIA,
          shaka.util.Error.Code.MP4_SIDX_WRONG_BOX_TYPE);
    }
  }


  /**
   * Parse a SIDX box from the given reader.
   *
   * @param {number} sidxOffset
   * @param {shaka.media.InitSegmentReference} initSegmentReference
   * @param {number} timestampOffset
   * @param {number} appendWindowStart
   * @param {number} appendWindowEnd
   * @param {!Array<string>} uris The possible locations of the MP4 file that
   *   contains the segments.
   * @param {!shaka.extern.ParsedBox} box
   * @param {boolean=} indexIsExternal sidx file is external to the media
   * @return {!Array<!shaka.media.SegmentReference>}
   * @private
   */
  static parseSIDX_(
      sidxOffset, initSegmentReference, timestampOffset, appendWindowStart,
      appendWindowEnd, uris, box, indexIsExternal = false) {
    goog.asserts.assert(
        box.version != null,
        'SIDX is a full box and should have a valid version.');

    const references = [];

    // Parse the SIDX structure.
    // Skip reference_ID (32 bits).
    box.reader.skip(4);

    const timescale = box.reader.readUint32();

    if (timescale == 0) {
      shaka.log.error('Invalid timescale.');
      throw new shaka.util.Error(
          shaka.util.Error.Severity.CRITICAL,
          shaka.util.Error.Category.MEDIA,
          shaka.util.Error.Code.MP4_SIDX_INVALID_TIMESCALE);
    }

    let earliestPresentationTime;
    let firstOffset;

    if (box.version == 0) {
      earliestPresentationTime = box.reader.readUint32();
      firstOffset = box.reader.readUint32();
    } else {
      earliestPresentationTime = box.reader.readUint64();
      firstOffset = box.reader.readUint64();
    }

    // Skip reserved (16 bits).
    box.reader.skip(2);

    // Add references.
    const referenceCount = box.reader.readUint16();

    // Subtract the presentation time offset
    let unscaledStartTime = earliestPresentationTime;
    // For external SIDX (index fetched from a different file), the spec
    // anchors first_offset at the start of the media segment. Re-anchor by
    // subtracting the box size so the initial start byte is |firstOffset|.
    const anchorOffset = indexIsExternal ? -box.size : sidxOffset;
    let startByte = anchorOffset + box.size + firstOffset;

    for (let i = 0; i < referenceCount; i++) {
      // |chunk| is 1 bit for |referenceType|, and 31 bits for |referenceSize|.
      const chunk = box.reader.readUint32();
      const referenceType = (chunk & 0x80000000) >>> 31;
      const referenceSize = chunk & 0x7FFFFFFF;

      const subsegmentDuration = box.reader.readUint32();

      // Skipping 1 bit for |startsWithSap|, 3 bits for |sapType|, and 28 bits
      // for |sapDelta|.
      box.reader.skip(4);

      // If |referenceType| is 1 then the reference is to another SIDX.
      // We do not support this.
      if (referenceType == 1) {
        shaka.log.error('Hierarchical SIDXs are not supported.');
        throw new shaka.util.Error(
            shaka.util.Error.Severity.CRITICAL,
            shaka.util.Error.Category.MEDIA,
            shaka.util.Error.Code.MP4_SIDX_TYPE_NOT_SUPPORTED);
      }

      // The media timestamps inside the container.
      const nativeStartTime = unscaledStartTime / timescale;
      const nativeEndTime =
          (unscaledStartTime + subsegmentDuration) / timescale;

      references.push(
          new shaka.media.SegmentReference(
              nativeStartTime + timestampOffset,
              nativeEndTime + timestampOffset,
              (() => { return uris; }),
              startByte,
              startByte + referenceSize - 1,
              initSegmentReference,
              timestampOffset,
              appendWindowStart,
              appendWindowEnd));

      unscaledStartTime += subsegmentDuration;
      startByte += referenceSize;
    }

    box.parser.stop();
    return references;
  }
};