static registerTransmuxer(mimeType, plugin, priority) {
    const TransmuxerEngine = shaka.transmuxer.TransmuxerEngine;
    const normalizedMimetype = TransmuxerEngine.normalizeMimeType_(mimeType);
    const key = normalizedMimetype + '-' + priority;
    TransmuxerEngine.transmuxerMap_.set(key, {
      priority: priority,
      plugin: plugin,
    });
  }
@param {string} mimeType
@param {!shaka.extern.TransmuxerPlugin} plugin
@param {number} priority
@export