First to make sure you can get video playback, please try playing a youtube video. You can also check if a normal HD video file will play to find out if your format was the problem. Here is a good example video: http://distribution.bbb3d.renderfarming.net/video/mp4/bbb_sunflower_1080p_30fps_normal.mp4
It could also be because your videos are mpeg-2 which needs a license key for Raspberry Pi’s. You can activate it in the Raspberry Settings.