Correlation between 2 signals of uneven dimensions
The intuitive way to go about this would be to consider every single pixel in your video (assuming that's only intensity, not e.g. color) a 1D signal over time.

Then you'd get width×height number of crosscorrelation functions between pixel intensities and your audio.

The different sampling rates of audio and video just mean that you'd need to reduce your audio to a signal of a rate that is identical to the video frame rate. (You could also interpolate the video to the audio rate, but then you'd be mostly making statements about the correlation properties of your interpolation function, not of your video).

The question is how you can reduce your audio to something that only takes say 25 values in a second. My wild guess is that this is something where you either use your inherent ideas of what would be a clever measure (e.g. "loudness in 40ms steps") or you just do the same for all 12.5 Hz wide bandwidths of your audio, and see which correlates best.