使用PHImageManager获取视频asset

[[PHImageManager defaultManager] requestAVAssetForVideo:asset options:self.videoOptions resultHandler:^(AVAsset * _Nullable avasset, AVAudioMix * _Nullable audioMix, NSDictionary * _Nullable info) {
    AVURLAsset *urlAsset = (AVURLAsset *)avasset;
    NSURL *url = urlAsset.URL;
    [self getVideoFirstImageWithUrl:url];
}];

- (PHVideoRequestOptions *)videoOptions {
    if (!_videoOptions) {
        _videoOptions = [[PHVideoRequestOptions alloc] init];
        _videoOptions.version = PHVideoRequestOptionsVersionOriginal;
        _videoOptions.deliveryMode = PHVideoRequestOptionsDeliveryModeAutomatic;
        _videoOptions.networkAccessAllowed = YES;
    }
    return _videoOptions;
}

后面两个子方法取自YBImageBrowser框架

#pragma mark - 获取视频的第一帧截图, 返回UIImage (需要导入AVFoundation.h)

- (UIImage *)getVideoFirstImageWithUrl:(NSURL *)url {
    AVAsset *asset = [AVAsset assetWithURL:url];
    // 也可直接传入AVURLAsset类型, AVURLAsset是AVAsset的子类
    AVAssetImageGenerator *generator = [AVAssetImageGenerator assetImageGeneratorWithAsset:asset];
    generator.appliesPreferredTrackTransform = YES;
    generator.maximumSize = CGSizeMake(500, 500);
    NSError *error = nil;
    CGImageRef cgImage = [generator copyCGImageAtTime:CMTimeMake(0, 1) actualTime:NULL error:&error];
    CGImageRef decodedImage = YYCGImageCreateDecodedCopy(cgImage, YES);
    UIImage *resultImage = [UIImage imageWithCGImage:decodedImage];
    if (cgImage) CGImageRelease(cgImage);
    if (decodedImage) CGImageRelease(decodedImage);
    return resultImage;
}

CGImageRef YYCGImageCreateDecodedCopy(CGImageRef imageRef, BOOL decodeForDisplay) {
    if (!imageRef) return NULL;
    size_t width = CGImageGetWidth(imageRef);
    size_t height = CGImageGetHeight(imageRef);
    if (width == 0 || height == 0) return NULL;

    if (decodeForDisplay) { //decode with redraw (may lose some precision)
        CGImageAlphaInfo alphaInfo = CGImageGetAlphaInfo(imageRef) & kCGBitmapAlphaInfoMask;
        BOOL hasAlpha = NO;
        if (alphaInfo == kCGImageAlphaPremultipliedLast ||
            alphaInfo == kCGImageAlphaPremultipliedFirst ||
            alphaInfo == kCGImageAlphaLast ||
            alphaInfo == kCGImageAlphaFirst) {
            hasAlpha = YES;
        }
        // BGRA8888 (premultiplied) or BGRX8888
        // same as UIGraphicsBeginImageContext() and -[UIView drawRect:]
        CGBitmapInfo bitmapInfo = kCGBitmapByteOrder32Host;
        bitmapInfo |= hasAlpha ? kCGImageAlphaPremultipliedFirst : kCGImageAlphaNoneSkipFirst;
        CGContextRef context = CGBitmapContextCreate(NULL, width, height, 8, 0, YYCGColorSpaceGetDeviceRGB(), bitmapInfo);
        if (!context) return NULL;
        CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef); // decode
        CGImageRef newImage = CGBitmapContextCreateImage(context);
        CFRelease(context);
        return newImage;

    } else {
        CGColorSpaceRef space = CGImageGetColorSpace(imageRef);
        size_t bitsPerComponent = CGImageGetBitsPerComponent(imageRef);
        size_t bitsPerPixel = CGImageGetBitsPerPixel(imageRef);
        size_t bytesPerRow = CGImageGetBytesPerRow(imageRef);
        CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
        if (bytesPerRow == 0 || width == 0 || height == 0) return NULL;

        CGDataProviderRef dataProvider = CGImageGetDataProvider(imageRef);
        if (!dataProvider) return NULL;
        CFDataRef data = CGDataProviderCopyData(dataProvider); // decode
        if (!data) return NULL;

        CGDataProviderRef newProvider = CGDataProviderCreateWithCFData(data);
        CFRelease(data);
        if (!newProvider) return NULL;

        CGImageRef newImage = CGImageCreate(width, height, bitsPerComponent, bitsPerPixel, bytesPerRow, space, bitmapInfo, newProvider, NULL, false, kCGRenderingIntentDefault);
        CFRelease(newProvider);
        return newImage;
    }
}

CGColorSpaceRef YYCGColorSpaceGetDeviceRGB() {
    static CGColorSpaceRef space;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        space = CGColorSpaceCreateDeviceRGB();
    });
    return space;
}

作者链接：https://www.jianshu.com/p/166c6f62b56d