来自 CALayer (AVPlayerLayer) 的 OpenGL 纹理

Question

我有一个 AVPlayerLayer，我想用它创建一个 OpenGL 纹理。我对 opengl 纹理很满意，甚至对将 CGImageRef 转换为 opengl 纹理也很满意。在我看来，下面的代码应该可以工作，但我得到的只是纯黑色。我究竟做错了什么？我需要先在 CALayer / AVPlayerLayer 上设置任何属性吗？

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

int width = (int)[layer bounds].size.width;
int height = (int)[layer bounds].size.height;

CGContextRef context = CGBitmapContextCreate(NULL,
                                 width,
                                 height,
                                 8,
                                 width * 4,
                                 colorSpace,
                                 kCGImageAlphaPremultipliedLast);

CGColorSpaceRelease(colorSpace);

if (context== NULL) {
    ofLog(OF_LOG_ERROR, "getTextureFromLayer: failed to create context 1");
    return;
}

[[layer presentationLayer] renderInContext:context];

CGImageRef cgImage = CGBitmapContextCreateImage(context);

int bytesPerPixel   = CGImageGetBitsPerPixel(cgImage)/8;
if(bytesPerPixel == 3) bytesPerPixel = 4;

GLubyte *pixels     = (GLubyte *) malloc(width * height * bytesPerPixel);

CGContextRelease(context);
context = CGBitmapContextCreate(pixels,
                                width,
                                height,
                                CGImageGetBitsPerComponent(cgImage),
                                width * bytesPerPixel,
                                CGImageGetColorSpace(cgImage),
                                kCGImageAlphaPremultipliedLast);

if(context == NULL) {
    ofLog(OF_LOG_ERROR, "getTextureFromLayer: failed to create context 2");
    free(pixels);
    return;
}

CGContextDrawImage(context, CGRectMake(0.0, 0.0, width, height), cgImage);

int glMode;
switch(bytesPerPixel) {
    case 1:
        glMode = GL_LUMINANCE;
        break;
    case 3: 
        glMode = GL_RGB;
        break;
    case 4: 
    default:
        glMode = GL_RGBA; break;
}

if(texture.bAllocated() == false || texture.getWidth() != width || texture.getHeight() != height) {
    NSLog(@"getTextureFromLayer: allocating texture %i, %i\n", width, height);
    texture.allocate(width, height, glMode, true);
}

// test texture
//        for(int i=0; i<width*height*4; i++) pixels[i] = ofRandomuf() * 255;

texture.loadData(pixels, width, height, glMode);

CGContextRelease(context);
CFRelease(cgImage);
free(pixels);

附：变量“纹理”是一个 C++ opengl（-es 兼容）纹理对象，我知道它可以工作。如果我取消注释“测试纹理”for-loop 用随机噪声填充纹理，我可以看到，所以问题肯定在之前。

更新

为了回应 Nick Weaver 的回复，我尝试了一种不同的方法，现在我总是从 copyNextSampleBuffer 返回 NULL，状态 == 3 (AVAssetReaderStatusFailed)。我错过了什么吗？

变量

AVPlayer                *videoPlayer;
AVPlayerLayer           *videoLayer;
AVAssetReader           *videoReader;
AVAssetReaderTrackOutput*videoOutput;

初始化

    videoPlayer = [[AVPlayer alloc] initWithURL:[NSURL fileURLWithPath:[NSString stringWithUTF8String:videoPath.c_str()]]];

    if(videoPlayer == nil) {
        NSLog(@"videoPlayer == nil ERROR LOADING %s\n", videoPath.c_str());
    } else {
        NSLog(@"videoPlayer: %@", videoPlayer);
        videoLayer = [[AVPlayerLayer playerLayerWithPlayer:videoPlayer] retain];
        videoLayer.frame = [ThreeDView instance].bounds;
        // [[ThreeDView instance].layer addSublayer:videoLayer]; // test to see if it's loading and running

        AVAsset *asset = videoPlayer.currentItem.asset;
        NSArray *tracks = [asset tracksWithMediaType:AVMediaTypeVideo];
        NSDictionary *settings = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA], (NSString*)kCVPixelBufferPixelFormatTypeKey, nil];

        videoReader = [[AVAssetReader alloc] initWithAsset:asset error:nil];
        videoOutput = [[AVAssetReaderTrackOutput alloc] initWithTrack:[tracks objectAtIndex:0] outputSettings:settings];
        [videoReader addOutput:videoOutput];
        [videoReader startReading];
    }

绘制循环

    if(videoPlayer == 0) {
        ofLog(OF_LOG_WARNING, "Shot::drawVideo: videoPlayer == 0");
        return;
    }


    if(videoOutput == 0) {
        ofLog(OF_LOG_WARNING, "Shot::drawVideo: videoOutput == 0");
        return;
    }

    CMSampleBufferRef sampleBuffer = [videoOutput copyNextSampleBuffer];

    if(sampleBuffer == 0) {
        ofLog(OF_LOG_ERROR, "Shot::drawVideo: sampleBuffer == 0, status: %i", videoReader.status);
        return;
    }


    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    CFRelease(sampleBuffer);

    CVPixelBufferLockBaseAddress(imageBuffer,0); 

    unsigned char *pixels = ( unsigned char *)CVPixelBufferGetBaseAddress(imageBuffer); 

    int width = CVPixelBufferGetWidth(imageBuffer); 
    int height = CVPixelBufferGetHeight(imageBuffer);

    if(videoTexture.bAllocated() == false || videoTexture.getWidth() != width || videoTexture.getHeight() != height) {
        NSLog(@"Shot::drawVideo() allocating texture %i, %i\n", width, height);
        videoTexture.allocate(width, height, GL_RGBA, true);
    }

    videoTexture.loadData(pixels, width, height, GL_BGRA);

    CVPixelBufferUnlockBaseAddress(imageBuffer,0);

Answer 1

我认为iOS4: how do I use video file as an OpenGL texture? 会对您的问题有所帮助。