Sticking jumping speeding up and slowing down


hi, can anyone help, I use h7s box wooshbuild infinity iptv feed and on some channels the video freezes then speeds up to catch up to the audio, then freezes again and repeats this process, making most main channels unwatchable. I was advise to shut down for over 60 secs but this makes no difference and has always happened. Any ideas what I need to look at or check? Ta