因为需要在相机界面实时缩放，效率原因，不采取CMSampleBufferRef转cgimage在缩放。

暂时找到的方法是通过vImage来缩放，代码如下，缩放成功返回得到的CVImageBuffer，转化为uiimage可以显示到imageView，却无法转化为CVMetalTextureRef（因为需要对缩放的CVImageBuffer进行滤镜操作）。
其他方式 https://www.jianshu.com/p/ac79a80f1af2

    CVImageBufferRef imageBuffer =CMSampleBufferGetImageBuffer(sampleBuffer);



vImage_Error ret;

    // Create dest buffer

    constNSUIntegerscale =1;

    constNSUIntegerdstWidth = (NSUInteger)fitSize.width* scale;

    constNSUIntegerdstHeight = (NSUInteger)fitSize.height* scale;

    constNSUIntegerbytesPerPixel =4;

    constNSUIntegerdstBytesPerRow = bytesPerPixel * dstWidth;

    uint8_t* dstData = (uint8_t*)calloc(dstHeight * dstWidth * bytesPerPixel,sizeof(uint8_t));

    vImage_BufferdstBuffer = {

        .data= dstData,

        .height= dstHeight,

        .width= dstWidth,

        .rowBytes= dstBytesPerRow,

    };



    // Scale

    ret =vImageScale_ARGB8888(&srcBuffer, &dstBuffer, NULL, kvImageHighQualityResampling);

//    free(srcBuffer.data);

    if (ret != kvImageNoError)

    {

        free(dstData);

        returnnil;

    }



    CVPixelBufferRef pxbuffer =NULL;

    NSDictionary *options =@{(NSString *)kCVPixelBufferCGImageCompatibilityKey:@YES,(NSString *)kCVPixelBufferCGBitmapContextCompatibilityKey:@YES,(NSString *)kCVPixelBufferMetalCompatibilityKey:@YES};

    CVReturnstatus =CVPixelBufferCreateWithBytes(kCFAllocatorDefault, fitSize.width, fitSize.height,kCVPixelFormatType_32BGRA, dstData, dstBuffer.rowBytes,nil,nil, (__bridgeCFDictionaryRef)options, &pxbuffer);

    return pxbuffer;

滤镜操作无法完成，代码如下

CVMetalTextureRef thumbMetalTexture;

            CVReturnssstatus =  CVMetalTextureCacheCreateTextureFromImage(kCFAllocatorDefault,self.thumbTextureCache, thttt,NULL,MTLPixelFormatBGRA8Unorm,50,50,0, &thumbMetalTexture);

            if(ssstatus !=0) {

                NSLog(@"%d",ssstatus);

                return;

            }

ssstatus = -6660，原因未知。