Adapted from https://github.com/bootladder/audioprocessor.
Note: Just in case someone else finds this useful, I figured that a simple pass-through for the STM32F746G-DISCO can be obtained adapting https://github.com/STMicroelectronics/STM32CubeF7/blob/master/Projects/STM32746G-Discovery/Examples/BSP/Src/audio_loopback.c from the STM32Cube repo. It mostly requires changing this line https://github.com/STMicroelectronics/STM32CubeF7/blob/master/Drivers/BSP/STM32746G-Discovery/stm32746g_discovery_audio.c#L893 such that it allows INPUT_DEVICE_INPUT_LINE_1 too and fixing the gain of the wm8994 codec here https://github.com/STMicroelectronics/STM32CubeF7/blob/master/Drivers/BSP/Components/wm8994/wm8994.c#L310 from 0x0035 to 0x0025 (both right and left channel).