I have been able to burn at least 450 calories in about 45 to 50 minutes.  YES indeed.  You read it correctly.  Just the other day, I was watching a recorded version of one of my favorite hour long shows after I put my one year old down for the night.  Before I pressed play, I put on a pair of tennis shoes and something comfortable that allowed me to move freely.  I then proceeded to press play and began doing jumping jacks.  I did that for a period of time, then I followed up with jogging in place, burpees, squats, the Groucho walks, lunges, etc all in no particular order.  I did this while watching my  TV show.  I rested when it was time for me to fast forward through the commercials.  Once the show was over, I looked down at my heart rate monitor and discovered that I had burned over 450 calories.  Wowsa!!!  I did this all while watching TV.  You can even incorporate push ups, resistance bands, weights, and all of that good stuff.