entropy VS ent.hpp

You can also look for patterns in the file that would suggest it's not encrypted, or just feed it into some kind of entropy measurement utility. If there's high entropy >7.5, then these files are actually encrypted with some key that was included in a manifest/MPD file or supplied to your browser client via a side-channel and is not included in these data files.

A header-only library that does the same thing and more. ent.hpp - applies various tests to sequences of bytes stored in files and reports the results of those tests. The class is useful for evaluating pseudorandom number generators for encryption and statistical sampling applications, compression algorithms, and other applications where the information density of a file is of interest. Gives you the following result: Entropy = 7.990144 bits per byte. Optimum compression would reduce the size of this 469842 byte file by 0 percent. Chi square distribution for 469842 samples is 6481.037481, and randomly would exceed this value less than 0.01 percent of the times. Arithmetic mean value of data bytes is 127.740998 (127.500000 = random). Monte Carlo value for Pi is 3.104039 (error 1.195363 percent). Serial correlation coefficient is -0.016080 (totally uncorrelated = 0.0).