这是一个使用Android Camera2 API和MediaCodec来编码H.264单元的示例代码：

import android.Manifest;
import android.app.Activity;
import android.content.pm.PackageManager;
import android.graphics.SurfaceTexture;
import android.hardware.camera2.CameraAccessException;
import android.hardware.camera2.CameraCaptureSession;
import android.hardware.camera2.CameraCharacteristics;
import android.hardware.camera2.CameraDevice;
import android.hardware.camera2.CameraManager;
import android.hardware.camera2.CaptureRequest;
import android.hardware.camera2.params.StreamConfigurationMap;
import android.media.MediaCodec;
import android.media.MediaCodecInfo;
import android.media.MediaFormat;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.util.Size;
import android.view.Surface;
import android.view.TextureView;

import androidx.annotation.NonNull;
import androidx.core.app.ActivityCompat;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.Arrays;

public class MainActivity extends Activity {

    private static final String TAG = "Camera2MediaCodec";
    private static final int PERMISSION_REQUEST_CAMERA = 0;

    private CameraManager cameraManager;
    private String cameraId;
    private Size previewSize;
    private TextureView textureView;
    private CameraDevice cameraDevice;
    private CaptureRequest.Builder captureRequestBuilder;
    private CameraCaptureSession cameraCaptureSession;
    private MediaCodec mediaCodec;
    private Surface inputSurface;

    private final MediaCodec.Callback mediaCodecCallback = new MediaCodec.Callback() {
        @Override
        public void onInputBufferAvailable(@NonNull MediaCodec codec, int index) {
            // Handle input buffer availability
            ByteBuffer inputBuffer = codec.getInputBuffer(index);
            // TODO: Fill inputBuffer with data to be encoded
            codec.queueInputBuffer(index, 0, /* size */, /* presentationTimeUs */, /* flags */);
        }

        @Override
        public void onOutputBufferAvailable(@NonNull MediaCodec codec, int index, @NonNull MediaCodec.BufferInfo info) {
            // Handle output buffer availability
            ByteBuffer outputBuffer = codec.getOutputBuffer(index);
            // TODO: Process encoded outputBuffer
            codec.releaseOutputBuffer(index, /* render */);
        }

        @Override
        public void onError(@NonNull MediaCodec codec, @NonNull MediaCodec.CodecException e) {
            // Handle codec errors
            Log.e(TAG, "MediaCodec error: " + e.getMessage());
        }

        @Override
        public void onOutputFormatChanged(@NonNull MediaCodec codec, @NonNull MediaFormat format) {
            // Handle output format change
            // TODO: Update codec's output format if needed
        }
    };

    private final TextureView.SurfaceTextureListener surfaceTextureListener = new TextureView.SurfaceTextureListener() {
        @Override
        public void onSurfaceTextureAvailable(SurfaceTexture surfaceTexture, int width, int height) {
            // Open camera when surface texture is available
            openCamera();
        }

        @Override
        public void onSurfaceTextureSizeChanged(SurfaceTexture surfaceTexture, int width, int height) {
            // Handle surface texture size change if needed
        }

        @Override
        public boolean onSurfaceTextureDestroyed(SurfaceTexture surfaceTexture) {
            // Release resources when surface texture is destroyed
            releaseCamera();
            return true;
        }

        @Override
        public void onSurfaceTextureUpdated(SurfaceTexture surfaceTexture) {
            // Handle surface texture update if needed
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textureView = findViewById(R.id.textureView);
        textureView.setSurfaceTextureListener(surfaceTextureListener);

        cameraManager = (CameraManager) getSystemService(CAMERA_SERVICE);
        try {
            String[] cameraIds = cameraManager.getCameraIdList();
            for (String id : cameraIds) {
                CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(id);
                if (characteristics.get(CameraCharacteristics.LENS_FACING) == CameraCharacteristics.LENS_FACING_BACK) {
                    cameraId = id;
                    break;
                }
            }
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    private void openCamera() {
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.CAMERA}, PERMISSION_REQUEST_CAMERA);
            return;
        }

        try {
            StreamConfigurationMap map = cameraManager.getCameraCharacteristics(cameraId).get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
            if (map != null) {
                previewSize = map.getOutputSizes(SurfaceTexture.class)[0]; // Choose appropriate size
            }

            cameraManager.openCamera(cameraId, cameraStateCallback, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    private void startPreview()