Why don't you try this - "Ab Workouts Express",this app targets every muscle in and around your abs with different fun moves. I am using this app for the past two months and I could feel the difference in my abs. I fell in love with it after using it, you can never find a better app. This makes me feel like I am working out with my trainer in the comfort at my own pace. I love the exercises and what I like most about the app is keeping track of when I do my workouts. I've been doing sit ups on an inclined bench for a long time with loads of reps with no real improvement. Tried this App just two months back and it's a bit of a killer to begin with. I'm sure there are other apps or videos but this one ticks all the boxes for me. Its just a matter of 5-10 mins daily workout and you are done. Trust me its so so amazing!!