getChannelsCount_(tag) {
    const channels = tag.getAttributeValue('CHANNELS');
    if (!channels) {
      return null;
    }
    const channelCountString = channels.split('/')[0];
    const count = parseInt(channelCountString, 10);
    return count;
  }
Get the channel count information for an HLS audio track.
CHANNELS specifies an ordered, "/" separated list of parameters.
If the type is audio, the first parameter will be a decimal integer
specifying the number of independent, simultaneous audio channels.
No other channels parameters are currently defined.

@param {!shaka.hls.Tag} tag
@return {?number}
@private