Given something like 103 data points ($N=103$), a DFT will give back 103 frequency values. Then to do something like filtering the high frequencies involves setting the high frequency values from the DFT to zero, and doing the inverse DFT to get back 103 data points that represent the original signal without the high frequencies.
This makes sense to me given all 103 data points all at once. But what about streaming an audio WAV file that is rather large (say for example $N=10^5$). If one wanted to filter the high frequencies then the approach i just described on the entire data of $10^5$ points logically makes sense. But that is not reasonable when streaming a WAV file for playback. What is done to high frequency filter a streaming playback of an audio file?