X squared x 3.14 to the power of 9, then take the square root times the common denominator. Use Franklin's law of compression to find value Y, add the two sums and there you have it, EZ PZ
if you really know about video file format, you will know that video size depends on many things. The compression, key frame, etc take the role. For new video guy or potential owners, getting such info may not be that easy.