Audio pass-through STM32F769I-Discovery Line in buffer copied to Line out
This software builds heavily on the great work by https://community.st.com/people/Beaulier.Francois
wm8994.c is modified from the BSP version
Input Mixer L and R zeroed and muted registers 0x29 and 0x2A
Read the data sheet. I know its long and complicated. Do it anyway.
SW4STM32 project using STM32 HAL
Output on serial port looks like
Connected to STM32F769I-Discovery USART 1

Audio I/O initialization OK
SAI receive begin OK
Copying Record buffer to Playback buffer
Audio output OK

Line level input is expected, not speaker level so turn your volume down at least to 50% or lower

I have not tested microphone input or speaker output