openGL ES 在android中将mp4视频格式转换为RGB图像的代码解析

首先，将 mp4 视频文件加载进来，可以使用 Android 系统提供的 MediaPlayer 类来实现。

MediaPlayer mediaPlayer = new MediaPlayer();
mediaPlayer.setDataSource(videoFilePath);
mediaPlayer.prepare();
mediaPlayer.start();

然后，创建一个 SurfaceView 用于显示视频画面，同时获取该 SurfaceView 的 SurfaceHolder 对象，以及该 SurfaceView 的宽高信息。

SurfaceView surfaceView = new SurfaceView(context);
SurfaceHolder surfaceHolder = surfaceView.getHolder();
surfaceHolder.addCallback(new SurfaceHolder.Callback() {
    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        mediaPlayer.setDisplay(holder);
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        // 获取 SurfaceView 的宽高信息
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {

    }
});

接下来，创建一个 OpenGL ES 的上下文环境，并初始化纹理、着色器等信息。

EGLContext eglContext = EGL14.eglGetCurrentContext();
EGLDisplay eglDisplay = EGL14.eglGetCurrentDisplay();
EGLSurface eglSurface = EGL14.eglGetCurrentSurface(EGL14.EGL_DRAW);

int[] attribList = {
        EGL14.EGL_RENDERABLE_TYPE, EGL14.EGL_OPENGL_ES2_BIT,
        EGL14.EGL_SURFACE_TYPE, EGL14.EGL_PBUFFER_BIT,
        EGL14.EGL_RED_SIZE, 8,
        EGL14.EGL_GREEN_SIZE, 8,
        EGL14.EGL_BLUE_SIZE, 8,
        EGL14.EGL_ALPHA_SIZE, 8,
        EGL14.EGL_NONE
};
EGLConfig[] configs = new EGLConfig[1];
int[] numConfigs = new int[1];
EGL14.eglChooseConfig(eglDisplay, attribList, 0, configs, 0, configs.length, numConfigs, 0);

int[] attribList2 = {
        EGL14.EGL_WIDTH, surfaceWidth,
        EGL14.EGL_HEIGHT, surfaceHeight,
        EGL14.EGL_NONE
};
EGLSurface eglSurface2 = EGL14.eglCreatePbufferSurface(eglDisplay, configs[0], attribList2, 0);
EGL14.eglMakeCurrent(eglDisplay, eglSurface2, eglSurface2, eglContext);

int[] textureIds = new int[1];
GLES20.glGenTextures(1, textureIds, 0);
GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, textureIds[0]);
GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_S, GLES20.GL_CLAMP_TO_EDGE);
GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_T, GLES20.GL_CLAMP_TO_EDGE);
GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MIN_FILTER, GLES20.GL_LINEAR);
GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MAG_FILTER, GLES20.GL_LINEAR);

接着，通过 MediaPlayer 的 onFrameAvailableListener 回调函数获取视频的每一帧数据，并将其转换为 RGB 图像。

mediaPlayer.setSurface(surfaceHolder.getSurface());
mediaPlayer.setOnVideoSizeChangedListener(new MediaPlayer.OnVideoSizeChangedListener() {
    @Override
    public void onVideoSizeChanged(MediaPlayer mp, int width, int height) {
        // 更新视频宽高信息
    }
});
mediaPlayer.setOnSeekCompleteListener(new MediaPlayer.OnSeekCompleteListener() {
    @Override
    public void onSeekComplete(MediaPlayer mp) {
        // 重新开始播放视频
        mediaPlayer.start();
    }
});

final float[] textureTransformMatrix = new float[16];
SurfaceTexture surfaceTexture = new SurfaceTexture(textureIds[0]);
surfaceTexture.setDefaultBufferSize(videoWidth, videoHeight);
surfaceTexture.setOnFrameAvailableListener(new SurfaceTexture.OnFrameAvailableListener() {
    @Override
    public void onFrameAvailable(SurfaceTexture surfaceTexture) {
        surfaceTexture.getTransformMatrix(textureTransformMatrix);

        GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, textureIds[0]);
        surfaceTexture.updateTexImage();

        ByteBuffer pixelBuffer = ByteBuffer.allocateDirect(videoWidth * videoHeight * 4);
        pixelBuffer.order(ByteOrder.LITTLE_ENDIAN);
        GLES20.glReadPixels(0, 0, videoWidth, videoHeight, GLES20.GL_RGBA, GLES20.GL_UNSIGNED_BYTE, pixelBuffer);
        pixelBuffer.rewind();

        byte[] pixelArray = new byte[videoWidth * videoHeight * 3];
        int index = 0;
        while (pixelBuffer.hasRemaining()) {
            pixelArray[index++] = pixelBuffer.get();
            pixelArray[index++] = pixelBuffer.get();
            pixelArray[index++] = pixelBuffer.get();
            pixelBuffer.get();
        }

        // 处理 RGB 图像数据
    }
});

最后，需要在程序退出时释放资源。

surfaceTexture.release();

EGL14.eglMakeCurrent(eglDisplay, EGL14.EGL_NO_SURFACE, EGL14.EGL_NO_SURFACE, EGL14.EGL_NO_CONTEXT);
EGL14.eglDestroySurface(eglDisplay, eglSurface2);
EGL14.eglMakeCurrent(eglDisplay, eglSurface, eglSurface, eglContext);
GLES20.glDeleteTextures(1, textureIds, 0);

mediaPlayer.stop();
mediaPlayer.release();