This code help users to record sound and dump into SD card, later use ffmpeg and batch script to format into WAV

1. ESP32 I2S devices
2. FFmpeg in %PATH% (Windows system in this case) Tutorial link by wikihow
3. SD Card

Screen shot of serial monitor (BUADRATE: 115200)

1. Continue outputing 's' means in "stand by mode", waiting for start command 'a' input.

2. Enter file name

3. Enter recording time (sec)

4. Wait for *** DONE WRITING *** shows up and insert SD Card into PC

5. Run i2s_to_wav.bat in folder where .i2s file locates (etc. SD Card)

6. File would be format into wav file with timestamp

• 2023/07/27 Recording result sounds slightly faster, maybe due to mismatch of sample rate cause by SD card write time.