The RPi4 has audio out (though it can drive headphones I don't think it is meant as a headphone socket, more line-level) but there isn't a microphone input in the base unit, you'd need an add-on HAT or USB to get audio-in. The fourth connection on the TRRS jack is for composite video output.Raspberry Pi 4 is small, lighter than the Nano developer kit, has audio (headphones output and microphone input).
Paeryn is right. Since the Pi 1B+ the AV socket has had four connections. Left Audio, Right Audio, Ground and Composite Video. All outputs.
The title of the your blog current reads "Jetson Nano and Rspberry Pi 4."energyi wrote: ↑Sat Nov 30, 2019 8:46 pmIf anyone is interested in a comparison of the Jetson Nano to the RPI4 I wrote up a comparison including the audio and video capabilities.
https://other2funstuff.blogspot.com/201 ... -pi-4.html
And just as heads up Microcenter has lowered prices on some RPI4s in store. And Newegg has a lowered price Nano. Hope this helps. No vested interests, just addicted to SBCs.