append_(contentType, data, timestampOffset, stream) {
    this.appendDependency(data, timestampOffset, stream);

    // This will trigger an 'updateend' event.
    this.sourceBuffers_.get(contentType).appendBuffer(data);
  }
Append data to the SourceBuffer.
@param {shaka.util.ManifestParserUtils.ContentType} contentType
@param {BufferSource} data
@param {number} timestampOffset
@param {shaka.extern.Stream} stream
@private