Would this be a Bluetooth interference problem or something else ?

[MathWizard]

I just got some BT earbuds and I'm using them with a MP3 player that has a touch screen. And so far in a few hours I used them, with them in my coat pocket and the screen locked, the mp3 track has moved back 1 file, and another time it seemed to skip a few tracks ahead or back IDR.

I don't know the circuits in this MP3 player, but if you just have some external switches and pins into a MCU, can the RF from the BT be enough to make the MCU think the button was pushed, turning on some gate or base of a transistor ?

I walked ~12km (7.5mil) 2 days ago, using wired earbuds, and never had the track skip ahead to another track once.

Maybe some cap in the switch circuit is dodgey and the BT RF puts energy into the circuit and puts it over the edge ?

But there is no external track skip button, that's all on screen. But there is a button for locking the screen.

[tom66]

Almost certainly not Bluetooth.

A common fault with switches especially on portable products is grime/sweat/moisture gets into the switches and forms conductive bridges which make the player think the buttons are randomly pressed.

A possible solution would be to gently clean the switches (once disassembled) with some IPA.

It's possible to save money/pins on the MCU they use an analog divider to select different functions.  So one voltage encodes play, another encodes stop, and so on.  If the missing voltage is being generated by a conductive bridge it could access 'unavailable' functions. 

[coppice]

Its easy to interrupt BT communications with interference, but accidentally faking an action is hard, as there is error checking on the received data.

[MathWizard]

Sometimes it did happen with wired HP, but not lately until yesterday/today with the BT ones. IDK maybe moisture gets in there, and yeah the touch screen seems to do funny stuff when snow falls on it, or getting pushed in in a pocket the wrong way. Or maybe yeah something is just wearing out.

I've pulled apart MP3 players before, and it's always been a black box problem. Power would work, and besides some ram and the MCU, there's not much to check. And IDK MCU hacking so I get nowhere.

[wasedadoc]

The Bluetooth AVRCP profile (https://en.wikipedia.org/wiki/List_of_Bluetooth_profiles) provides control of the player from the audio (and video) output device.  If your player and earbuds implement that profile it is possible that you have unknowingly activated track skips by touching the earbuds.  Consult the manual for the earbuds.