Maybe this is a dumb question, but when I run a test render on the first 100 frames or so everything looks great - renders in HD to H.264 in MPEG-4 with H.264 codec and MP3 audio codec, everything in the sample render looks and sounds like I want it to. However, when I extend the end frame to the full video length (31,049 frames) the resulting mp4 file won't play anything in VLC media player or Windows Media Player.
I'm not sure why the short render works but the long one doesn't? The only thing I'm changing between renders is the end frame.
For reference, I'm on Windows 10 using Blender 2.76b. I'm by no means a power user, but it seems that whether I render using my CPU or my GPU I end up with the same thing - short render gives me a good result, but long render won't play for anything.