Tvheadend

Good evening, I'm new, I installed tvheadend on a raspberry pi with TV-Shield DVB-T2, as far as digital terrestrial is concerned everything is ok,
I use coreelec on odroid platforms and it works wonders, I wanted to add iptv channels but most of these you see the video but they are without sound, do I have to install special codecs? as main system i installed dietpi. Thank you.
Ps. it is possible to insert ready-made m3u files without using the usual http ... there is a tutorial. thank you.