HDMI audio to external tv drops out intermittently; headphone socket audio lags behind external tv

I am using a 13" MacBook Pro early 2015. I can successfully link it to an external LG tv using an HDMI cable. However, the sound intermittently and frequently momentarily drops out. There seems to be a delay in the next portion of incoming sound, not just a silent part: by this I mean that a musical playback loses time across the error, and the incoming sound is late, rather than just part of the sound being absent. Somehow it always seems to remain in sync with the picture overall, and there is no discernible stutter in the picture.

If I instead use the audio from the headphone socket, it plays without errors, but as the tv picture has a delay as compared to the Mac screen, picture and sound are now always out of sync.

How can I rectify the HDMI issue?