A digital-to-analog converter (DAC or D-to-A) is a system that converts a digital signal into an analog signal. DACs are commonly used in music players to convert digital data streams into analog audio signals. Audio DACs generally low-frequency and high-resolution. [Wikipedia]

The ESP32 has two internal 8bit DACs. These DACs can convert any 8 bit value to an analog voltage output. The 0-255 8-bit input values map roughly to the voltage range of 0V to 3.3V on the ESP32. A digitized audio sample can be played it back through the DAC.

Check out the example sketch shown here as internalDACsimple.ino to see what happens when you sample a sine wave and push the samples out to the internal DAC.

The video shows a demo doing this with some Pac-Man game sounds. This is basically doing the same thing but with more complex sampled signals than the points on a sine curve. You can try out the Tutorial and Code for the Pac-Man sounds in this link from Barton Dring.

Remember that we are only using the internal DAC inside the ESP32 so you can grab the analog signal directly from ESP32 pin 25 and ground. The external DAC is not needed. The analog signal from pin 25 can go directly into some earbuds or amplified speaker inputs, but it cannot really drive a speaker on its own.