Deinterlace interlaced frames 

MPEG2 videos can be interlaced. 
If not de-interlaced at playback time, this can produce some artifacts (stripes appear on the video).
These extra few lines cater with this issue.
![before](https://f.cloud.github.com/assets/403701/66329/e9decb6a-5ea0-11e2-8ace-0ae9b6c06bf9.png)
![after](https://f.cloud.github.com/assets/403701/66331/ef31b582-5ea0-11e2-8558-e7296b3c24a4.png)