DVD

“Dr. Horrible’s Sing-Along Blog” (out Tuesday). Joss Whedon’s musical about a lovelorn would-be supervillain and the video blog he records in his home doesn’t exactly scream surefire hit, but it took the Internet by storm last summer. This sweet and sinister tale about the eponymous mad scientist (Neil Patrick Harris) who battles his arch nemesis, Captain Hammer (Nathan Fillion, of Whedon’s dearly departed “Firefly”), for the affections of the crusading civilian Penny (Felicia Day) shot immediately to the top of the iTunes video chart, and was viewed over 2.2 million times in its first week. If you missed it then, here’s your chance to discover it.”