, I used the 4-line earphones to connect Banana Pro's AV port, then heard a burst of other sounds, after some discussion, let us find the reason, come and go!
It is well known that the Banana Pro's AV port can output audio signal, but in fact the AV port also output video signal, which is a composite audio and video signal output interface, there are four level interface
The main difference between these two standards is that different definitions of microphone interfaces and ground interfaces. There are many adapter cable for conversion between the two standards.
In short words, Pro's AV port is designed to output a composite video signal, allowing users easy to use RCA interface display, so you should use a 3-line TRS earphone or AV cable(as follows) to connect to it.
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