Two things are important here, your taxonomy is portfoliosets, which mean this is not a built-in category. videos and magazines are terms of your taxonomy. From what I can make from your question, you need to show different header image for different single post page view depending on the term a post belongs to.
Based on this, you can use the has_term( $term, $taxonomy, $post ) conditional tag to check if a post belongs to a certain term. I just want to point out one little mistake here, is_single( $post ) doesn’t take the term as parameter, only the post’s ID, name or slug.
I would suggest that you make use of is_singular( $post_types ) to check for your single post page.
After all this, your query should be something like this
if(is_singular( 'portfolios')){
if(has_term( 'videos', 'portfoliosets' )){
<---DO SOMETHING FOR TERM video--->
}elseif(has_term( 'magazine', 'portfoliosets' )){
<---DO SOMETHING FOR TERM magazine--->
}else{
<---DO SOMETHING ELSE FOR OTHER POSTS--->
}
}