When you upload a video to MediaSilo, we create an .mp4 proxy. This proxy is the file used for playback across MediaSilo. We do this because playback occurs on many different browsers and devices, each of which has its own requirements for video format, codec, and more. The file you upload to MediaSilo may not meet these requirements, which would cause playback to fail– in either some or all browsers and devices. To prevent these playback issues, we create a proxy that plays on all browsers and devices. Note that when a person downloads a file from MediaSilo, they will download the original .mov that you uploaded, not the proxy.
To learn more, please see our article on Uploading Web-Playable Files.