Getting current player buffer size (Android native)

Hi, I am using Android's native JWPlayer. I want to get the player's current video buffer size (seconds of playback remaining). I have looked into the API documentation but I have not found a suitable method for getting it. I also did not find anything useful on the Internet. There is VideoPlayerEvents.OnBufferChangeListener(), but it does not seem to get called at all. There is also VideoPlayerEvents.OnTimeListener(), but the 'duration' parameter is always set to -1. Does anyone know the correct / customary way to get JWPlayer's current buffer size in native Android apps, or is it not possible? Thanks in advance ;)