Samsung 48" uhd TV optical sound not working on apps only television channels

[Strattly]

Have Samsung 48" uhd TV which outputs optical sound just fine from television channels but if switch to say YouTube app or iView just generates horrible static/crackling sound through amplifier

 

[Strattly]

Naim amplifier only accepts digital in PCM format so need to change output on TV to PCM (not Dolby) and switch Dolby compression to "RF" (not "line")