Ive user nPlayer for a few months now and whilst it works well, there are some issues. Playing MKV files through the Apple Lightning-HDMI adapter works but the video cannot play when the device is paused. MP4 files do not have this limitation.
Bit streaming Dolby audio through the Apple HDMI adapter broke in version 3.2.4 and is still broken 3.2.6. 3.2.3 still works. Regressions like this are especially frustrating after paying extra for the Dolby decoder.
Ryley Angus about nPlayer Plus