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标题: ios - AVSampleBufferDisplayLayer 不在设备上呈现 [打印本页]

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作者: 菜鸟教程小白    时间: 2022-12-13 12:59
标题: ios - AVSampleBufferDisplayLayer 不在设备上呈现

我在 iOS 上使用 AVSampleBufferDisplayLayer 时遇到了困难。我想使用这个层显示一个 CVPixelBuffer，但我无法让它在实际的 iOS 设备上工作。在我的示例应用程序中，我尝试使用以下代码来显示一种颜色像素缓冲区:

@implementation ViewController {
    AVSampleBufferDisplayLayer *videoLayer;
}

- (void)viewDidLoad {
    [super viewDidLoad];

    videoLayer = [[AVSampleBufferDisplayLayer alloc] init];
    videoLayer.frame = CGRectMake(50, 50, 300, 300);
    videoLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;

    [self.view.layer addSublayer:videoLayer];
}

@implementation ViewController {
    AVSampleBufferDisplayLayer *videoLayer;
}

- (void)viewDidLoad {
    [super viewDidLoad];

    videoLayer = [[AVSampleBufferDisplayLayer alloc] init];
    videoLayer.frame = CGRectMake(50, 50, 300, 300);
    videoLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;

    [self.view.layer addSublayer:videoLayer];
}

- (void)viewDidAppearBOOL)animated {
    [super viewDidAppear:animated];
    [self startVideo];
}

- (void)startVideo {
    [self drawPixelBuffer];
    [NSTimer scheduledTimerWithTimeInterval:0.1 target:self selectorselector(drawPixelBuffer) userInfo:nil repeats:YES];
}

- (void)drawPixelBuffer {

    int imageSize = 100;

    static const uint8_t pixel[] = {0x00, 0xAA, 0xFF, 0xFF};

    NSMutableData *frame = [NSMutableData data];

    for (int i = 0; i < imageSize * imageSize; i++) {
        [frame appendBytes:pixel length:4];
    }

    CVPixelBufferRef pixelBuffer = NULL;

    CVPixelBufferCreateWithBytes(NULL, imageSize, imageSize, kCVPixelFormatType_32BGRA, [frame bytes], imageSize * 4, NULL, NULL, NULL, &pixelBuffer);

    CMSampleBufferRef sampleBuffer = [self sampleBufferFromPixelBuffer:pixelBuffer];

    if (sampleBuffer) {

        [videoLayer enqueueSampleBuffer:sampleBuffer];
        CFRelease(sampleBuffer);

    }

}

- (CMSampleBufferRef)sampleBufferFromPixelBufferCVPixelBufferRef)pixelBuffer {

    CMSampleBufferRef sampleBuffer = NULL;
    OSStatus err = noErr;
    CMVideoFormatDescriptionRef formatDesc = NULL;
    err = CMVideoFormatDescriptionCreateForImageBuffer(kCFAllocatorDefault, pixelBuffer, &formatDesc);

    if (err != noErr) {
        return nil;
    }

    CMSampleTimingInfo sampleTimingInfo = kCMTimingInfoInvalid;

    err = CMSampleBufferCreateReadyWithImageBuffer(kCFAllocatorDefault, pixelBuffer, formatDesc, &sampleTimingInfo, &sampleBuffer);

    if (sampleBuffer) {
        CFArrayRef attachments = CMSampleBufferGetSampleAttachmentsArray(sampleBuffer, YES);
        CFMutableDictionaryRef dict = (CFMutableDictionaryRef)CFArrayGetValueAtIndex(attachments, 0);
        CFDictionarySetValue(dict, kCMSampleAttachmentKey_DisplayImmediately, kCFBooleanTrue);
    }

    if (err != noErr) {
        return nil;
    }

    formatDesc = NULL;

    return sampleBuffer;

}

@end

这在 iOS 模拟器中运行没有任何问题，但在真实设备上无法运行(没有渲染)。视频层的错误属性始终为 nil，状态始终等于 AVQueuedSampleBufferRenderingStatusRendering。

感谢您的帮助。

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Best Answer-推荐答案

模拟器中的图形实现要健壮得多，而且您通常可以摆脱在设备上无法运行的东西。常见的原因有两种:

像素缓冲区应该由 IOSurface 支持

您正在通过 CVPixelBufferCreateWithBytes 直接映射该缓冲区。再次尝试使用 CVPixelBufferCreate 并将 kCVPixelBufferIOSurfacePropertiesKey 属性设置为空字典。

CVPixelBufferCreate(
    NULL,
    imageSize,
    imageSize,
    kCVPixelFormatType_32BGRA,
    (__bridge CFDictionaryRef)@{
        (id)kCVPixelBufferIOSurfacePropertiesKey: @{}
    },
    &pixelBuffer);
CVPixelBufferLockBaseAddress(pixelBuffer, 0);
void *bytes = CVPixelBufferGetBaseAddress(pixelBuffer);
// Write image data directly to that address
CVPixelBufferUnlockBaseAddress(pixelBuffer, 0);

实际上，任何生成这些像素的东西都应该尽可能直接写入 CVPixelBufferRef。

设备不支持某些格式

这对于 kCVPixelFormatType_32BGRA 来说似乎极不可能，但我已经看到了仅模拟器支持，例如 kCVPixelFormatType_422YpCbCr8。在这些情况下，必须首先将其转换为兼容格式，或者必须实现自定义渲染器(OpenGL、Metal 等)。

关于ios - AVSampleBufferDisplayLayer 不在设备上呈现，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/35365008/

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