It is illegal in most countries to post any copyrighted work without explicit consent of the creator/publisher. Probably nothing will happen to you, but be careful, my friend got sued by Metallica when we were 15 because he shared their songs on Napster. You never know who might come after you.
Safer way (but still a grey area) is to post links to other sites or to use YouTubes sharing function which would be ok, as google does monitor and remove anything that is infringing on copyrights.
Best thing for your blog is to keep it to your own material, writings and thoughts, rather than posting other peoples works unless you're authorized to review, promote or publicize for them.