使用 AVAssetWriter 捕获屏幕 - 在模拟器上运行良好，但在设备上会产生黑色视频

Question

我正在尝试捕获帧缓冲区数据并将其转换为我的 iPhone 游戏的视频。 我使用 AVAssetWriter 来完成这件事。 该代码在模拟器上运行良好，但在设备本身上运行不佳。在设备上它会生成一个黑色视频，

我使用以下代码：

//This code initializes the AVAsetWriter and other things

- (void) testVideoWriter {
    CGRect screenBoundst = [[UIScreen mainScreen] bounds];
    //initialize global info
    MOVIE_NAME = @"Documents/Movie5.mp4";
    //CGSize size = CGSizeMake(screenBoundst.size.width, screenBoundst.size.height);
    CGSize size = CGSizeMake(320, 480);
    frameLength = CMTimeMake(1, 5); 
    currentTime = kCMTimeZero;
    currentFrame = 0;

    MOVIE_PATH = [NSHomeDirectory() stringByAppendingPathComponent:MOVIE_NAME];
    NSError *error = nil;

    videoWriter = [[AVAssetWriter alloc] initWithURL:[NSURL fileURLWithPath:MOVIE_PATH]
                                            fileType:AVFileTypeMPEG4 error:&error];

    NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:AVVideoCodecH264, AVVideoCodecKey,
                                   [NSNumber numberWithInt:size.width ], AVVideoWidthKey,
                                   [NSNumber numberWithInt:size.height ], AVVideoHeightKey, nil];

    writerInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:videoSettings];

    NSDictionary *sourcePixelBufferAttributesDictionary = [NSDictionary dictionaryWithObjectsAndKeys:
                                                           [NSNumber numberWithInt:kCVPixelFormatType_32BGRA],
                                                           kCVPixelBufferPixelFormatTypeKey, nil];

    adaptor = [AVAssetWriterInputPixelBufferAdaptor assetWriterInputPixelBufferAdaptorWithAssetWriterInput:
               writerInput sourcePixelBufferAttributes:sourcePixelBufferAttributesDictionary];
    [adaptor retain];

    CGAffineTransform flipVertical = CGAffineTransformMake(1, 0, 0, -1, 0, self.frame.size.height);
    flipVertical = CGAffineTransformRotate(flipVertical,(90.0*3.14f/180.0f));
    [writerInput setTransform:flipVertical];

    [videoWriter addInput:writerInput];

    [videoWriter startWriting];
    [videoWriter startSessionAtSourceTime:kCMTimeZero];

    VIDEO_WRITER_IS_READY = true;
}

//this code capture the screen data
- (void) captureScreenVideo {

    if (!writerInput.readyForMoreMediaData) {
        return;
    }

    CGRect screenBounds = [[UIScreen mainScreen] bounds];
    NSLog(@"width : %f Height : %f",screenBounds.size.width,screenBounds.size.height);
    CGSize esize = CGSizeMake(screenBounds.size.width, screenBounds.size.height);
    NSInteger myDataLength = esize.width * esize.height * 4;
    GLuint *buffer = (GLuint *) malloc(myDataLength);
    glReadPixels(0, 0, esize.width, esize.height, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
    CVPixelBufferRef pixel_buffer = NULL;
    NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                             [NSNumber numberWithBool:YES], kCVPixelBufferCGImageCompatibilityKey,
                             [NSNumber numberWithBool:YES], kCVPixelBufferCGBitmapContextCompatibilityKey,
                             nil];
    CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault, esize.width,
                                          esize.height, kCVPixelFormatType_32BGRA, (CFDictionaryRef) options, 
                                          &pixel_buffer);
    NSParameterAssert(status == kCVReturnSuccess && pixel_buffer != NULL);

    CVPixelBufferLockBaseAddress(pixel_buffer, 0);
    void *pxdata = CVPixelBufferGetBaseAddress(pixel_buffer);
    NSParameterAssert(pixel_buffer != NULL);

    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(pxdata, esize.width,
                                                 esize.height, 8, 4*esize.width, rgbColorSpace, 
                                                 kCGImageAlphaNoneSkipFirst);
    NSParameterAssert(context);

    CGAffineTransform flipVerticalq = CGAffineTransformMake(1, 0, 0, -1, 0, self.frame.size.height);
    flipVerticalq = CGAffineTransformRotate(flipVerticalq,(90.0*3.14f/180.0f));
    CGContextConcatCTM(context, flipVerticalq);

    CGColorSpaceRelease(rgbColorSpace);
    CGContextRelease(context);

    CVPixelBufferUnlockBaseAddress(pixel_buffer, 0);

    if(![adaptor appendPixelBuffer:pixel_buffer withPresentationTime:currentTime]) {
        NSLog(@"FAIL");
    } else {
        NSLog(@"Success:%d", currentFrame);
        currentTime = CMTimeAdd(currentTime, frameLength);
    }

    free(buffer);
    CVPixelBufferRelease(pixel_buffer);
}

// this code saves the video to library on device itself
- (void) moveVideoToSavedPhotos {

    ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
    NSString *localVid = [NSHomeDirectory() stringByAppendingPathComponent:MOVIE_NAME];    
    NSURL* fileURL = [NSURL fileURLWithPath:localVid];
        NSLog(@"movie saved %@",fileURL);
    BOOL isVideoOK = UIVideoAtPathIsCompatibleWithSavedPhotosAlbum(localVid);
    if (NO == isVideoOK)
        NSLog(@"Video at %@ is not compatible",localVid);
    else {
        NSLog(@"video ok");
    }

    [library writeVideoAtPathToSavedPhotosAlbum:fileURL
                                completionBlock:^(NSURL *assetURL, NSError *error) {
                                    if (error) {   
                                        NSLog(@"%@: Error saving context: %@", [self class], [error localizedDescription]);
                                    }
                                }];
    [library release];
}

// following code stops the video recording after particular number of frames

    if (VIDEO_WRITER_IS_READY) {
        [self captureScreenVideo];
        currentFrame++;

        if (currentFrame > 500) {
            VIDEO_WRITER_IS_READY = false;
            [writerInput markAsFinished];

            if (![videoWriter finishWriting]) {
                NSLog(@"writing not finished");
            }

            CVPixelBufferPoolRelease(adaptor.pixelBufferPool); 
            [writerInput release];
            [videoWriter release]; 


            NSLog(@"saving the file");
            [self moveVideoToSavedPhotos];
        }
    }

此外，当模拟器上捕获的视频是镜像视频时...我不知道我错在哪里.. .请向我澄清这件事...并希望你们不介意阅读整个代码..