Android : Android FFmpeg Video Recording Delete Last Recorded Part

Hello I'm trying to do exactly what the picture shows. Her is the Link http://www.makeuseof.com/tag/the-ultimate-guide-to-instagram-video-everything-you-need-to-know/.

Anyway how to do this so i can delete a partial video part. The code i was testing with is on github. Here is the link https://github.com/qdrzwd/VideoRecorder

Can someone help me figure it out how to delete partial recordings thanks.