setInitSegmentReference(uris, startByte, endByte, mediaQuality) {
    goog.asserts.assert(this.manifest_,
        'A top-level generated Manifest is required to use this method!');

    const getUris = () => uris;
    this.initSegmentReference_ =
        new this.manifest_.shaka_.media.InitSegmentReference(
            getUris, startByte, endByte, mediaQuality);
  }
Sets the init segment of the current stream.

@param {!Array<string>} uris
@param {number} startByte
@param {?number} endByte
@param {null|shaka.extern.MediaQualityInfo=} mediaQuality