Found out that Perfect Player had exatly the same problem as Smart IPTV at first, but if I changed to hardware decoder it ran smoothly.
Lets hope they can fix the Smart IPTV app for Android TV, becouse I like that app better than Perfect Player / Kodi.
I got the same android tv (Sony bravia kdl 55w809c) and same problem with smart iptv app. I live in sweden so I'm watching the swedish channels. They lag/buffer horrible. Is there no settings for that app?
Or do we have to use another app? Perfect Player doesent sound that good with no 5.1 and...