isVideoOnly() {
    if (this.manifest_ && !this.isRemotePlayback()) {
      const variants = this.manifest_.variants;
      if (!variants.length) {
        return false;
      }

      const firstVariant = variants[0];
      if (firstVariant.audio || !firstVariant.video) {
        return false;
      }
      return !firstVariant.video.codecs.includes(',');
    } else if (this.video_ && (this.video_.src || this.isRemotePlayback())) {
      if (this.video_.audioTracks) {
        return this.video_.audioTracks.length == 0;
      }
    }
    return false;
  }
Check if the manifest contains only video-only content. If the player has
not loaded content, this will return <code>false</code>.

<p>
The player does not support content that contain more than one type of
variants (i.e. mixing audio-only, video-only, audio-video). Content will be
filtered to only contain one type of variant.

@return {boolean}
@export