Noise estimation SNR matrix
In your case you probably want to calculate the SNR as mean over standard deviation.

signal=rand([256,192,330]); %demo data
SNR = mean(signal,3)./std(signal,[],3);
SNRdb = 10*log10(SNR);


this way you obtain different SNR values per pixel. 256x192 pixels in 330 frames.

To get the values for each of the 330 frames instead you must first reshape your matrix.

signal=reshape(signal,[],330);  %pixel values merged
SNR = mean(signal)./std(signal);
SNRdb = 10*log10(SNR);