Video background grid overlay issue?

This is probably a really obvious mistake that i'm missing, but anyway: I'm having an issue with using a video as a...

ffprobe output video: png?

ffprobe is telling me that my video file is a png. [png_pipe @ 0x7f9ece003c00] Stream #0: not enough frames to esti...

M4V Mimetype - video/mp4 or video/m4v??

I am serving a video via the HTML5 video element. I'm finding conflicting information about the appropriate MIME typ...