mp4 video doesn't play in PowerPoint 2016

I'm using Windows 10 and Office 2016. 

I created a PPTX with an embedded mp4 using PowerPoint. It plays fine without any problem. Then I used OpenXml SDK2.5 productivity tool to generate C# code based on this pptx. Running the code generated another pptx file. I opened it and tried to play the video. It didn't play. I opened it in PowerPoint and tried to play it there. It showed "Codec Unavailable". Why? How do I insert video via OpenXml SDK 2.5? Why code generated by productivity tool doesn't work?

Thanks in advance!!!