You can't just redefine a murder video as pornographic because you don't like it. You mentioned the miller test, so you already know it requires that it depict "sexual conduct or excretory functions specifically defined by applicable state law".
Ignoring the state law requirement (which you haven't cited), the video does not depict sexual conduct.. and there's no way you can twist this into being illegal in the US. It's not illegal. Period. ISIS videos aren't illegal either.
You've clearly misunderstood our laws.