僅測試了本機(jī)拍攝的mp4文件

- (void)setFileName:(NSString *)fileName{
    _fileName = [fileName copy];
    
    // 這里是獲取本地沙盒的視頻，遠(yuǎn)程url原理一樣
    // 記住如果是http地址記得用[NSURL URLWithString:urlStr]
    // 若是本地視頻地址要用[NSURL fileURLWithPath:path]
    _videoUrl = [NSURL fileURLWithPath:[[[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject] stringByAppendingPathComponent:VideoRecordsDirectory] stringByAppendingPathComponent:_fileName]];
    
    AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:_videoUrl options:nil];
    
    // 獲取某一幀圖片，這里獲取第一幀
    _videoImage = [self getthumImageForAsset:asset atTime:0];
}

// 獲取視頻某一幀的圖片
- (UIImage *)getthumImageForAsset:(AVURLAsset *)asset atTime:(NSTimeInterval)time{
    
    NSParameterAssert(asset);
    
    AVAssetImageGenerator *assetImageGenerator = [[AVAssetImageGenerator alloc] initWithAsset:asset];
    assetImageGenerator.appliesPreferredTrackTransform = YES;
    assetImageGenerator.apertureMode = AVAssetImageGeneratorApertureModeEncodedPixels;
    
    // 獲取任意幀要設(shè)定這個(gè)，然后可根據(jù)傳過來的參數(shù)time獲取任意幀
    //    assetImageGenerator.requestedTimeToleranceAfter = kCMTimeZero;
    //    assetImageGenerator.requestedTimeToleranceBefore = kCMTimeZero;
    
    CGImageRef thumImageRef = NULL;
    
    // 獲取哪一時(shí)間的幀圖片
    CFTimeInterval thumImageTime = time;
    
    NSError *thumImageGenerationError = nil;
    
    // 獲取每秒多少幀
    //    float fps = [[[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] nominalFrameRate];
    // 重寫CMTimeMake(a,b) a當(dāng)前第幾幀, b每秒鐘多少幀.當(dāng)前播放時(shí)間a/b CMTimeMakeWithSeconds(a,b) a當(dāng)前時(shí)間,b每秒鐘多少幀
    // 這個(gè)時(shí)候即可獲取第N幀圖片
    //    thumImageRef = [assetImageGenerator copyCGImageAtTime:CMTimeMake(time, fps) actualTime:NULL error:&thumImageGenerationError];
    
    thumImageRef = [assetImageGenerator copyCGImageAtTime:CMTimeMake(thumImageTime, 60) actualTime:NULL error:&thumImageGenerationError];
    
    if (!thumImageRef)
        NSLog(@"thumImageGenerationError %@", thumImageGenerationError);
    
    UIImage *thumImage = thumImageRef ? [[UIImage alloc] initWithCGImage:thumImageRef] : nil;
    
    return thumImage;
}

/** 獲取視頻的尺寸 */
+ (void)getVideoSizeWithURL:(NSURL *)URL complete:(void(^)(CGSize videoSize))complete{
    
    AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:URL options:nil];
    
    // 獲取
    // loadValuesAsynchronouslyForKeys是官方提供異步加載track的方法，防止線程阻塞
    // 加載track是耗時(shí)操作
    [asset loadValuesAsynchronouslyForKeys:@[@"tracks"] completionHandler:^{
        
        // 一般視頻都有至少兩個(gè)track(軌道)，根據(jù)track.mediaType判斷track類型
        // AVMediaTypeVideo表示視頻軌道，AVMediaTypeAudio代表音頻軌道，其他類型可以查看文檔。
        // 根據(jù)track的naturalSize屬性即可獲得視頻尺寸
        NSArray *array = asset.tracks;
        CGSize videoSize = CGSizeZero;
        
        for (AVAssetTrack *track in array) {
            
            if ([track.mediaType isEqualToString:AVMediaTypeVideo]) {
                
                // 注意修正naturalSize的寬高
                videoSize = CGSizeApplyAffineTransform(track.naturalSize, track.preferredTransform);//CGSizeMake(track.naturalSize.height, track.naturalSize.width);
                
                break;
            }
        }
        
        if (asset.playable) {
            
            dispatch_async(dispatch_get_main_queue(), ^{
                
                !complete ? : complete(videoSize);
            });
        }
    }];
}