(In reply to Boyuan Zhang from comment #13)

> In the meantime, I will look at the ntsc framerate.

On this I looked what gstreamer and avconv were sending and both do send the
denominator so a v2 (horrible looking) patch attached which tests OK for a
variety of inputs.

I guess there's a more elegant way, but it works. Maybe over paranoid trying to
avoid division by 0 in this case, but I notice that the gop patch can get one
if the user asks for -g 0 with avconv.