[peter-ebert]

Whenever you're compressing a file on your computer the frequencies are known beforehand. Agree this does not apply to noisy-channel coding, only the Shannon source coding theorem in lossless compression. Good point though I'm not sure if this would be considered an entropy encoder, as previous values do have some impact. Any more info I should look at for that?

[gliptic]

> Whenever you're compressing a file on your computer the frequencies are known beforehand.

Not at all. The best compressors learn to predict the frequencies as they go, they do not compute them up front and store them in the output.

[foobarqux]

You still have to store that info and that counts against the number of bytes you are using