public long getCachedDuration() {
        return mExtractor.getCachedDuration();
    }
Returns the duration if the cached data in the extractor, or -1 if the extractor does not
support or does not need caching (e.g. local files).
@return the duration of the cached data or -1 if caching is not active
MediaPlayer/src/main/java/net/protyposis/android/mediaplayer/MediaCodecDecoder.java