/*
  ESP32-S2-EYE I2S record to WAV example
  This simple example demonstrates using the I2S library to record
  5 seconds of audio data and write it to a WAV file on the SD card.

  Don't forget to select the OPI PSRAM, 8MB flash size and Enable USB CDC
  on boot in the Tools menu!

  Created for arduino-esp32 on 18 Dec, 2023
  by Lucas Saavedra Vaz (lucasssvaz)
*/

#include "ESP_I2S.h"
#include "FS.h"
#include <SD.h>
#include <M5GFX.h>
M5GFX tft;
uint16_t RGB888toRGB565(uint32_t rgb888) {
	return ((rgb888 & 0x00F80000) >> 8) | ((rgb888 & 0x0000FC00) >> 5) | ((rgb888 & 0x000000F8) >> 3);
}

const uint8_t I2S_SCK = 43;
const uint8_t I2S_WS = -1;
const uint8_t I2S_DIN = 46;

const uint8_t SD_CMD = 14;
const uint8_t SD_CLK = 40;
const uint8_t SD_DATA0 = 39;

void setup() {
	// Create an instance of the I2SClass
	I2SClass i2s;

	// Create variables to store the audio data
	uint8_t *wav_buffer;
	size_t wav_size;

	// Initialize the serial port
	tft.init();
	tft.startWrite();
	tft.setBrightness(64);
	tft.fillScreen(RGB888toRGB565(0x66CCFF));
	tft.setCursor(0, 0);
	tft.setTextColor(RGB888toRGB565(0x003399));

	tft.println("Initializing I2S bus...");

	// Set up the pins used for audio input
	i2s.setPins(I2S_SCK, -1, -1, I2S_DIN);

	// Initialize the I2S bus in standard mode
	if (!i2s.begin(I2S_MODE_PDM_RX, 16000, I2S_DATA_BIT_WIDTH_16BIT, I2S_SLOT_MODE_MONO, I2S_STD_SLOT_RIGHT)) {
		tft.println("Failed to initialize I2S bus!");
		return;
	}

	tft.println("I2S bus initialized.");
	tft.println("Initializing SD card...");

	// Set up the pins used for SD card access
	SPI.begin(40, 39, 14, 12);/*SCLK, MISO, MOSI, CS*/
	SPI.setFrequency(40000000);

	// Mount the SD card
	if (!SD.begin()) {
		tft.println("Failed to initialize SD card!");
		return;
	}

	tft.println("SD card initialized.");
	tft.println("Recording 1 second of audio data...");

	// Record 5 seconds of audio data
	wav_buffer = i2s.recordWAV(1, &wav_size);

	// Create a file on the SD card
	File file = SD.open("/test.wav", FILE_WRITE);
	if (!file) {
		tft.println("Failed to open file for writing!");
		return;
	}

	tft.println("Writing audio data to file...");
	tft.printf("Size: %d bytes\n", wav_size);

	// Write the audio data to the file
	if (file.write(wav_buffer, wav_size) != wav_size) {
		tft.println("Failed to write audio data to file!");
		return;
	}

	// Close the file
	file.close();
	free(wav_buffer);

	tft.println("Application complete.");
	while (true);
}

void loop() {}

Please pay attention to the I2S initialization code.
I tried several different codes to init the I2S, but none of them could get the correct audio data.

if (!i2s.begin(I2S_MODE_PDM_RX, 16000, I2S_DATA_BIT_WIDTH_16BIT, I2S_SLOT_MODE_MONO, I2S_STD_SLOT_RIGHT)) {

This one fills 0x2987 into the WAV file, and it records no sound.

if (!i2s.begin(I2S_MODE_STD, 16000, I2S_DATA_BIT_WIDTH_16BIT, I2S_SLOT_MODE_MONO, I2S_STD_SLOT_RIGHT)) {

This one fills noise into the WAV file.

if (!i2s.begin(I2S_MODE_PDM_TX, 16000, I2S_DATA_BIT_WIDTH_16BIT, I2S_SLOT_MODE_MONO, I2S_STD_SLOT_RIGHT)) {

This one writes a 0 byte WAV file.
I have modified the other options of this function, but failed.

How can I use the onboard microphone with ESP_I2S.h library?