function setCodecs(codecs, level) {
  ['video', 'audio', 'text'].forEach(function (type) {
    var filtered = codecs.filter(function (codec) {
      return Object(_utils_codecs__WEBPACK_IMPORTED_MODULE_7__["isCodecType"])(codec, type);
    });

    if (filtered.length) {
      var preferred = filtered.filter(function (codec) {
        return codec.lastIndexOf('avc1', 0) === 0 || codec.lastIndexOf('mp4a', 0) === 0;
      });
      level[type + "Codec"] = preferred.length > 0 ? preferred[0] : filtered[0]; // remove from list

      codecs = codecs.filter(function (codec) {
        return filtered.indexOf(codec) === -1;
      });
    }
  });
  level.unknownCodecs = codecs;
}
Backfill any missing PDT values
"If the first EXT-X-PROGRAM-DATE-TIME tag in a Playlist appears after
one or more Media Segment URIs, the client SHOULD extrapolate
backward from that tag (using EXTINF durations and/or media
timestamps) to associate dates with those segments."
We have already extrapolated forward, but all fragments up to the first instance of PDT do not have their PDTs
computed.