How to recognize for small video sequence with a large sequence?
The most intuitive approach here would simply be taking every pixel's color values, and finding peaks in the individual pixels' reference video/short video cross correlation function. That's basically a W×H-dimensional crosscorrelation function; you could speed that up by doing fast convolution.

You could algorithmically reduce the effort by first reducing the dimensionality of your problem, for example by reducing each video frame to a global brightness value and a mean motion vector of e.g. the frame center region – then you'd only have to calculate a threedimensional crosscorellation function.