概述

    Android 获取视频缩略图的方法通常有:

1. ContentResolver: 使用系统数据库
2. MediaMetadataRetriever: 这个是android提供的类，用来获取本地和网络media相关文件的信息
3. ThumbnailUtils: 是在android2.2（api8）之后新增的一个，该类为我们提供了三个静态方法供我们使用。
4. MediaExtractor 与MediaMetadataRetriever类似
   然而, 这几种方法存在一定的局限性, 比如, ContentResolver需要视频文件已经通过mediascanner 添加到系统数据库中, 使用MediaMetadataRetriever不支持某些格式等等. 常规的格式比如MP4, MKV, 这些接口还是很实用的.

    对于系统不支持的播放的格式比如AVI等, 需要一个更丰富的接口或方法来获取视频的缩略图. 于是尝试使用OpenGLES 离屏渲染 + MediaPlayer来提取视频画面作为缩略图.

参考代码

参考:ExtractMpegFramesTest.java 改动, 使用MediaPlayer, 理论上, 只要使用MediaPlayer可以播放的视频, 都可以提取出视频画面.

import android.annotation.SuppressLint;
import android.graphics.Bitmap;
import android.graphics.SurfaceTexture;
import android.media.MediaPlayer;
import android.opengl.EGL14;
import android.opengl.EGLConfig;
import android.opengl.EGLContext;
import android.opengl.EGLDisplay;
import android.opengl.EGLSurface;
import android.opengl.GLES10;
import android.opengl.GLES11Ext;
import android.opengl.GLES20;
import android.os.Build;
import android.util.Log;
import android.view.Surface;import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;
import java.nio.IntBuffer;import javax.microedition.khronos.opengles.GL10;public class VideoFrameExtractorGL extends Thread implements MediaPlayer.OnSeekCompleteListener {final String TAG = "VFEGL";private MediaPlayer mediaPlayer;private Surface surface;private int bitmapWidth, bitmapHeight;private int textureId;private SurfaceTexture surfaceTexture;final Object drawLock = new Object();// Shader代码private String vertexShaderCode ="#version 300 es\n" +"in vec4 position;\n" +"in vec2 texCoord;\n" +"uniform mat4 uSTMatrix;\n" +"out vec2 vTexCoord;\n" +"\n" +"void main() {\n" +"    // \n" +"    float curvature = -0.5; // 曲率值，负值表示凹面\n" +"    vec4 pos = position;\n" +"    //pos.z = curvature * (pos.x * pos.x + pos.y * pos.y);\n" +"\n" +"    //if(pos.x > 0.0001) pos.y += 0.2;\n" +"\n" +"    gl_Position = pos;\n" +"    vTexCoord = (uSTMatrix * vec4(texCoord, 0.0, 1.0)).xy;\n" +"}";private String fragmentShaderCode ="#version 300 es\n" +"#extension GL_OES_EGL_image_external : require\n" +"precision mediump float;\n" +"\n" +"in vec2 vTexCoord;\n" +"uniform samplerExternalOES sTexture;\n" +"out vec4 fragColor;\n" +"\n" +"void main() {\n" +"    fragColor = texture(sTexture, vTexCoord);\n" +"}\n";protected float[] mSTMatrix = new float[16];protected int mProgram;private int mPositionHandle;private int mTexCoordHandle;private int mSTMatrixHandle;// 顶点坐标和纹理坐标private final float[] squareCoords = {-1.0f,  1.0f,   // top left1.0f,  1.0f,   // top right-1.0f, -1.0f,   // bottom left1.0f, -1.0f    // bottom right};private final float[] textureCoords = {0.0f, 0.0f,   // top left1.0f, 0.0f,   // top right0.0f, 1.0f,   // bottom left1.0f, 1.0f    // bottom right};private FloatBuffer vertexBuffer;private FloatBuffer textureBuffer;// EGL相关变量private EGLDisplay eglDisplay;private EGLContext eglContext;private EGLSurface eglSurface;boolean isPrepared = false;long videoDuration = 0;int videoWidth, videoHeight;String mPath;// 构造函数，初始化MediaPlayer并设置渲染大小public VideoFrameExtractorGL(String videoFile, int bitmapWidth, int bitmapHeight, OnFrameExtractListener l) {this.bitmapWidth = bitmapWidth;this.bitmapHeight = bitmapHeight;mPath = videoFile;setOnFrameExtractListener(l);}@Overridepublic void run() {mediaPlayer = new MediaPlayer();mediaPlayer.setVolume(0, 0);mediaPlayer.setOnSeekCompleteListener(this);initializeEGL();   // 初始化EGL环境initializeOpenGL(); // 初始化OpenGL离屏渲染环境try {mediaPlayer.setDataSource(mPath);mediaPlayer.setOnPreparedListener(new MediaPlayer.OnPreparedListener() {@Overridepublic void onPrepared(MediaPlayer mediaPlayer) {Log.d(TAG, "onPrepared start playing");isPrepared = true;videoDuration = mediaPlayer.getDuration();videoWidth = mediaPlayer.getVideoWidth();videoHeight = mediaPlayer.getVideoHeight();mediaPlayer.start();}});mediaPlayer.prepareAsync();} catch (Exception e) {e.printStackTrace();}int timeout = 20;while(!isPrepared){try {sleep(30);timeout--;if(timeout < 0){break;}} catch (InterruptedException ignore) {}}while(mediaPlayer != null) {drawFrameLoop();}}// 初始化EGL环境@SuppressLint("NewApi")private void initializeEGL() {Log.d(TAG, "initializeEGL");// 1. 获取默认的EGL显示设备eglDisplay = EGL14.eglGetDisplay(EGL14.EGL_DEFAULT_DISPLAY);if (eglDisplay == EGL14.EGL_NO_DISPLAY) {throw new RuntimeException("Unable to get EGL14 display");}// 2. 初始化EGLint[] version = new int[2];if (!EGL14.eglInitialize(eglDisplay, version, 0, version, 1)) {throw new RuntimeException("Unable to initialize EGL14");}// 3. 配置EGLint[] configAttributes = {EGL14.EGL_RED_SIZE, 8,EGL14.EGL_GREEN_SIZE, 8,EGL14.EGL_BLUE_SIZE, 8,EGL14.EGL_ALPHA_SIZE, 8,EGL14.EGL_RENDERABLE_TYPE, EGL14.EGL_OPENGL_ES2_BIT,EGL14.EGL_NONE};EGLConfig[] eglConfigs = new EGLConfig[1];int[] numConfigs = new int[1];EGL14.eglChooseConfig(eglDisplay, configAttributes, 0, eglConfigs, 0, 1, numConfigs, 0);if (numConfigs[0] == 0) {throw new IllegalArgumentException("No matching EGL configs");}EGLConfig eglConfig = eglConfigs[0];// 4. 创建EGL上下文int[] contextAttributes = {EGL14.EGL_CONTEXT_CLIENT_VERSION, 2,EGL14.EGL_NONE};eglContext = EGL14.eglCreateContext(eglDisplay, eglConfig, EGL14.EGL_NO_CONTEXT, contextAttributes, 0);if (eglContext == null) {throw new RuntimeException("Failed to create EGL context");}// 5. 创建离屏渲染的EGL Surfaceint[] surfaceAttributes = {EGL14.EGL_WIDTH, bitmapWidth,EGL14.EGL_HEIGHT, bitmapHeight,EGL14.EGL_NONE};eglSurface = EGL14.eglCreatePbufferSurface(eglDisplay, eglConfig, surfaceAttributes, 0);if (eglSurface == null) {throw new RuntimeException("Failed to create EGL Surface");}// 6. 绑定上下文if (!EGL14.eglMakeCurrent(eglDisplay, eglSurface, eglSurface, eglContext)) {throw new RuntimeException("Failed to bind EGL context");}}// 初始化OpenGL ES的离屏渲染，使用帧缓冲区private void initializeOpenGL() {Log.d(TAG, "initializeOpenGL");// 创建纹理并绑定int[] textureIds = new int[1];GLES20.glGenTextures(1, textureIds, 0);textureId = textureIds[0];// 绑定纹理并绘制//GLES20.glActiveTexture(GLES20.GL_TEXTURE0);GLES20.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, textureId);GLES20.glTexParameterf(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_MIN_FILTER,GLES20.GL_NEAREST);GLES20.glTexParameterf(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_MAG_FILTER,GLES20.GL_LINEAR);GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_WRAP_S,GLES20.GL_CLAMP_TO_EDGE);GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_WRAP_T,GLES20.GL_CLAMP_TO_EDGE);surfaceTexture = new SurfaceTexture(textureId);surfaceTexture.setOnFrameAvailableListener(new SurfaceTexture.OnFrameAvailableListener() {@Overridepublic void onFrameAvailable(SurfaceTexture surfaceTexture) {Log.d(TAG, "onFrameAvailable");synchronized (drawLock){drawLock.notifyAll();}}});// 创建Surface与MediaPlayer绑定surface = new Surface(surfaceTexture);mediaPlayer.setSurface(surface);// 初始化着色器createProgram(vertexShaderCode, fragmentShaderCode);// 在构造函数中初始化缓冲区vertexBuffer = ByteBuffer.allocateDirect(squareCoords.length * 4).order(ByteOrder.nativeOrder()).asFloatBuffer().put(squareCoords);vertexBuffer.position(0);textureBuffer = ByteBuffer.allocateDirect(textureCoords.length * 4).order(ByteOrder.nativeOrder()).asFloatBuffer().put(textureCoords);textureBuffer.position(0);}// 创建着色器程序private void createProgram(String vertexSource, String fragmentSource) {int vertexShader = loadShader(GLES20.GL_VERTEX_SHADER, vertexSource);int fragmentShader = loadShader(GLES20.GL_FRAGMENT_SHADER, fragmentSource);mProgram = GLES20.glCreateProgram();GLES20.glAttachShader(mProgram, vertexShader);GLES20.glAttachShader(mProgram, fragmentShader);GLES20.glLinkProgram(mProgram);GLES20.glUseProgram(mProgram);mPositionHandle = GLES20.glGetAttribLocation(mProgram, "position");mTexCoordHandle = GLES20.glGetAttribLocation(mProgram, "texCoord");mSTMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uSTMatrix");}// 加载着色器private int loadShader(int type, String shaderSource) {int shader = GLES20.glCreateShader(type);GLES20.glShaderSource(shader, shaderSource);GLES20.glCompileShader(shader);return shader;}final Object extractLock = new Object();int targetPosOfVideo;boolean seeking = false;//if ignore time check, add extracting to check if notify callback//or else, it will notify after player is started.boolean extracting = false;@SuppressLint("WrongConstant")public void extract(int posOfVideoInMs){synchronized (extractLock) {targetPosOfVideo = posOfVideoInMs;seeking = true;extracting = true;while (!isPrepared) {Log.w(TAG, "extract " + posOfVideoInMs + " ms failed: MediaPlayer is not ready.");try {Thread.sleep(15);} catch (InterruptedException ignore) {}}{if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {mediaPlayer.seekTo(posOfVideoInMs, MediaPlayer.SEEK_NEXT_SYNC);}else{mediaPlayer.seekTo(posOfVideoInMs);}}try {Log.d(TAG, "extract " + posOfVideoInMs + " ms, and start extractLock wait");extractLock.wait();} catch (InterruptedException e) {e.printStackTrace();}}}public void extract(float posRatio){while(!isPrepared){try {sleep(10);} catch (InterruptedException e) {throw new RuntimeException(e);}}int pos = (int)(posRatio * videoDuration);extract(pos);}// 截取指定时间的图像帧private void drawFrameLoop() {synchronized (drawLock) {long pos = mediaPlayer.getCurrentPosition();Log.d(TAG, "drawFrameLoop at " + pos  + " ms");surfaceTexture.updateTexImage();surfaceTexture.getTransformMatrix(mSTMatrix);GLES20.glViewport(0, 0, bitmapWidth, bitmapHeight);GLES10.glClearColor(color[0], color[1], color[2], 1.0f); // 设置背景颜色为黑色GLES10.glClear(GL10.GL_COLOR_BUFFER_BIT); // 清除颜色缓冲区GLES20.glUseProgram(mProgram);// 传递顶点数据vertexBuffer.position(0);GLES20.glEnableVertexAttribArray(mPositionHandle);GLES20.glVertexAttribPointer(mPositionHandle, 2, GLES20.GL_FLOAT, false, 0, vertexBuffer);// 传递纹理坐标数据textureBuffer.position(0);GLES20.glEnableVertexAttribArray(mTexCoordHandle);GLES20.glVertexAttribPointer(mTexCoordHandle, 2, GLES20.GL_FLOAT, false, 0, textureBuffer);// 传递纹理矩阵GLES20.glUniformMatrix4fv(mSTMatrixHandle, 1, false, mSTMatrix, 0);// 绘制纹理GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, vertexBuffer.limit() / 2);Bitmap bm = toBitmap();if(extracting && !seeking) {boolean notifyCallback = ignoreTimeCheck || (targetPosOfVideo > 0 && pos >= targetPosOfVideo);if(notifyCallback) {targetPosOfVideo = 0;if (oel != null) oel.onFrameExtract(this, bm);synchronized (extractLock) {Log.d(TAG, "drawFrameLoop notify extractLock");extractLock.notify();}}}try{drawLock.wait();}catch(Exception ignore){}}}public boolean isDone(){return mediaPlayer != null && targetPosOfVideo <= mediaPlayer.getCurrentPosition();}public Bitmap getBitmap(){return toBitmap();}IntBuffer pixelBuffer;private Bitmap toBitmap(){// 读取帧缓冲区中的像素if(pixelBuffer == null){pixelBuffer = IntBuffer.allocate(bitmapWidth * bitmapHeight);}else {pixelBuffer.rewind();}GLES20.glReadPixels(0, 0, bitmapWidth, bitmapHeight, GLES20.GL_RGBA, GLES20.GL_UNSIGNED_BYTE, pixelBuffer);// 创建Bitmap并将像素数据写入Bitmap bitmap = Bitmap.createBitmap(bitmapWidth, bitmapHeight, Bitmap.Config.ARGB_8888);pixelBuffer.position(0);bitmap.copyPixelsFromBuffer(pixelBuffer);return bitmap;}// 释放资源@SuppressLint("NewApi")public void release() {if (mediaPlayer != null) {mediaPlayer.release();}mediaPlayer = null;synchronized (drawLock){try {drawLock.wait(100);} catch (InterruptedException e) {e.printStackTrace();}drawLock.notifyAll();}if (surface != null) {surface.release();}if (eglSurface != null) {EGL14.eglDestroySurface(eglDisplay, eglSurface);}if (eglContext != null) {EGL14.eglDestroyContext(eglDisplay, eglContext);}if (eglDisplay != null) {EGL14.eglTerminate(eglDisplay);}GLES20.glDeleteTextures(1, new int[]{textureId}, 0);}float[] color = {0, 0, 0, 1f};public void setColor(float r, float g, float b){color[0] = r; color[1] = g; color[2] = b;}OnFrameExtractListener oel;public void setOnFrameExtractListener(OnFrameExtractListener l){oel = l;}@Overridepublic void onSeekComplete(MediaPlayer mediaPlayer) {Log.d(TAG, "onSeekComplete pos=" + mediaPlayer.getCurrentPosition());seeking = false;}public interface OnFrameExtractListener{void onFrameExtract(VideoFrameExtractorGL vfe, Bitmap bm);}public static Bitmap[] extractBitmaps(int[] targetMs, String path, int bmw, int bmh){final int len = targetMs.length;final Bitmap[] bms = new Bitmap[len];VideoFrameExtractorGL vfe = new VideoFrameExtractorGL(path, bmw, bmh, new OnFrameExtractListener() {int count = 0;@Overridepublic void onFrameExtract(VideoFrameExtractorGL vfe, Bitmap bm) {Log.d("VFEGL", "extractBitmaps");bms[count] = bm;count ++;if(count >= len){vfe.release();}}});vfe.start();for(int pos : targetMs){vfe.extract(pos);}Log.d("VFEGL", "extractBitmaps done");return bms;}boolean ignoreTimeCheck = false;public static Bitmap[] extractBitmaps(String path, int bmw, int bmh,final float durationRatio, final int bitmapCount){final Bitmap[] bms = new Bitmap[bitmapCount];VideoFrameExtractorGL vfe = new VideoFrameExtractorGL(path, bmw, bmh, new OnFrameExtractListener() {int count = 0;@Overridepublic void onFrameExtract(VideoFrameExtractorGL vfe, Bitmap bm) {Log.d("VFEGL", "extractBitmaps");bms[count] = bm;count ++;if(count >= bitmapCount){vfe.release();}}});vfe.start();vfe.ignoreTimeCheck = true;vfe.extract(durationRatio);Log.d("VFEGL", "extractBitmaps done");return bms;}
}

基本的流程如下:

1. 初始化MeidaPlayer 用与播放视频
2. 初始化OpenGL环境, 绑定Texture 和 SurfaceTexture
3. 使用SurfaceTexutre创建Surface, 并为MediaPlayer 设置Surface, 这样视频就会绘制到Surface上
4. 通过SurfaceTexture的setOnFrameAvailableListener回调绘制帧数据
5. 从OpenGL中提取出glReadPixels提取出像素数据, 填充到Bitmap

调用

		Bitmap[] bms = VideoFrameExtractorGL.extractBitmaps(path, 128, 72, 0.5f, bmCount);

需注意:

1. 注意OpenGLES 的版本, 1.x 不支持离屏渲染, 2.x 需要配合着色器渲染图像
2. 构建OpenGL的环境和渲染的工作, 要放在同一个线程中.

参考

Kotlin拿Android本地视频缩略图
Android视频图片缩略图的获取
Android 获取视频缩略图(获取视频每帧数据)的优化方案
37.4 OpenGL离屏渲染环境配置
ExtractMpegFramesTest.java