Ios 无法使CISourceOverCompositing工作

我使用CISOURCEOVERCOMPING合并图像并导出为CVPixelBuffer。当图像计数低于41时，一切正常。但当它达到42或更大时，结果变成全黑。这是我的处理代码：

- (CVPixelBufferRef)pixelBufferRefWithMergingStillMaterials:(NSArray *)materials withBackgroundSampleBuffer:(CMSampleBufferRef)sampleBuffer {
// 基于gpu合并所有图层

CVImageBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);

size_t width = CVPixelBufferGetWidth(pixelBuffer);
size_t height = CVPixelBufferGetHeight(pixelBuffer);

CIImage *backgroundImage = [CIImage imageWithCVPixelBuffer:pixelBuffer];

static int i = 0;
i=0;
CIFilter *filter = [CIFilter filterWithName:@"CISourceOverCompositing"];
// 合并静态素材到一个CIImage
for (id<MicroVideoStillMaterial> stillMaterial in materials) {

    CIImage *foregroundImage = [stillMaterial image];


    [filter setDefaults];
    [filter setValue:backgroundImage forKey:kCIInputBackgroundImageKey];
    [filter setValue:foregroundImage forKey:kCIInputImageKey];

    backgroundImage = filter.outputImage;
    i++;
}

NSLog(@"iiiiiiiiiii  %d", i);

EAGLContext *glContext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
CIContext *context = [CIContext contextWithEAGLContext:glContext];

CFDictionaryRef empty = CFDictionaryCreate(kCFAllocatorDefault, // EMPTY IOSURFACE DICT
                                           NULL,
                                           NULL,
                                           0,
                                           &kCFTypeDictionaryKeyCallBacks,
                                           &kCFTypeDictionaryValueCallBacks);
CFMutableDictionaryRef attributes = CFDictionaryCreateMutable(kCFAllocatorDefault,
                                                              1,
                                                              &kCFTypeDictionaryKeyCallBacks,
                                                              &kCFTypeDictionaryValueCallBacks);

CFDictionarySetValue(attributes,kCVPixelBufferIOSurfacePropertiesKey,empty);

CVPixelBufferRef outputPixelBuffer = NULL;

CVPixelBufferCreate(kCFAllocatorSystemDefault, width, height, kCVPixelFormatType_32BGRA, attributes, &outputPixelBuffer);
CVPixelBufferLockBaseAddress(outputPixelBuffer, 0);
[context render:backgroundImage toCVPixelBuffer:outputPixelBuffer];

CVPixelBufferUnlockBaseAddress(outputPixelBuffer, 0);

return outputPixelBuffer;
}

-（CVPixelBufferRef）PixelBufferRef与MergingStillMaterials:（NSArray*）材料与背景sampleBuffer:（CMSampleBufferRef）sampleBuffer{
// 基于gpu合并所有图层
CVImageBufferRef pixelBuffer=CMSampleBufferGetImageBuffer（sampleBuffer）；
size\u t width=CVPixelBufferGetWidth（pixelBuffer）；
大小\u t高度=CVPixelBufferGetHeight（pixelBuffer）；
CIImage*backgroundImage=[CIImage imageWithCVPixelBuffer:pixelBuffer]；
静态int i=0；
i=0；
CIFilter*过滤器=[CIFilter过滤器名称：@“CISOURCEOVERCOMPITING”]；
// 合并静态素材到一个CIImage
用于（材质中的材质id）{
CIImage*前景图像=[stillMaterial图像]；
[过滤器设置默认值]；
[过滤器设置值：backgroundImage forKey:KCIIInputBackgroundImageKey]；
[过滤器设置值：foregroundImage forKey:KCIIInputImageKey]；
backgroundImage=filter.outputImage；
i++；
}
NSLog（@“IIIII%d”，i）；
EAGLContext*glContext=[[EAGLContext alloc]initWithAPI:kEAGLRenderingAPIOpenGLES2]；
CIContext*context=[CIContext ContextWithEagleContext:glContext]；
CFDictionaryRef empty=CFDictionaryCreate（kCFAllocatorDefault，//空IOSURFACE DICT
无效的
无效的
0,
&kCFTypeDictionaryKeyCallBacks，
&kCFTypeDictionaryValueCallBacks）；
CFMutableDictionaryRef attributes=CFDictionaryCreateMutable（kCFAllocatorDefault，
1.
&kCFTypeDictionaryKeyCallBacks，
&kCFTypeDictionaryValueCallBacks）；
CFDictionarySetValue（属性，kCVPixelBufferIOSurfacePropertiesKey，空）；
CVPixelBufferRef outputPixelBuffer=NULL；
CVPixelBufferCreate（kCFAllocatorSystemDefault、宽度、高度、KCVPIXelFormattType_32BGRA、属性和输出PixelBuffer）；
CVPixelBufferLockBaseAddress（outputPixelBuffer，0）；
[上下文渲染：背景图像ToCpPixelBuffer:outputPixelBuffer]；
CVPixelBufferUnlockBaseAddress（outputPixelBuffer，0）；
返回输出像素缓冲区；
}

这段代码在后台线程中运行。任何人有任何想法，请帮助。谢谢