在一些視頻APP中，都可以看到一個(gè)將在線視頻轉(zhuǎn)成GIF圖的功能。下面就來說說思路以及實(shí)現(xiàn)。我們知道本地視頻可以生成GIF,那么將在線視頻截取成本地視頻不就可以了嗎？經(jīng)過比較，騰訊視頻App也是這么做的。話不多說，下面開始上代碼：
第一步：截取視頻

#pragma mark -截取視頻
/**
  @param videoUrl 視頻的URL
 @param outPath 輸出路徑
 @param outputFileType 輸出視頻格式
 @param videoRange 截取視頻的范圍
 @param completeBlock 視頻截取的回調(diào)
 */
- (void)interceptVideoAndVideoUrl:(NSURL *)videoUrl withOutPath:(NSString *)outPath outputFileType:(NSString *)outputFileType range:(NSRange)videoRange intercept:(InterceptBlock)interceptBlock {
    
    _interceptBlock =interceptBlock;
    
    //不添加背景音樂
    NSURL *audioUrl =nil;
    //AVURLAsset此類主要用于獲取媒體信息，包括視頻、聲音等
    AVURLAsset* audioAsset = [[AVURLAsset alloc] initWithURL:audioUrl options:nil];
    AVURLAsset* videoAsset = [[AVURLAsset alloc] initWithURL:videoUrl options:nil];
   
    //創(chuàng)建AVMutableComposition對(duì)象來添加視頻音頻資源的AVMutableCompositionTrack
    AVMutableComposition* mixComposition = [AVMutableComposition composition];
    
    //CMTimeRangeMake(start, duration),start起始時(shí)間，duration時(shí)長(zhǎng)，都是CMTime類型
    //CMTimeMake(int64_t value, int32_t timescale)，返回CMTime，value視頻的一個(gè)總幀數(shù)，timescale是指每秒視頻播放的幀數(shù)，視頻播放速率，（value / timescale）才是視頻實(shí)際的秒數(shù)時(shí)長(zhǎng)，timescale一般情況下不改變，截取視頻長(zhǎng)度通過改變value的值
    //CMTimeMakeWithSeconds(Float64 seconds, int32_t preferredTimeScale)，返回CMTime，seconds截取時(shí)長(zhǎng)（單位秒），preferredTimeScale每秒幀數(shù)
    
    //開始位置startTime
    CMTime startTime = CMTimeMakeWithSeconds(videoRange.location, videoAsset.duration.timescale);
    //截取長(zhǎng)度videoDuration
    CMTime videoDuration = CMTimeMakeWithSeconds(videoRange.length, videoAsset.duration.timescale);
    
    CMTimeRange videoTimeRange = CMTimeRangeMake(startTime, videoDuration);
    
    //視頻采集compositionVideoTrack
    AVMutableCompositionTrack *compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
    
    // 避免數(shù)組越界 tracksWithMediaType 找不到對(duì)應(yīng)的文件時(shí)候返回空數(shù)組
    //TimeRange截取的范圍長(zhǎng)度
    //ofTrack來源
    //atTime插放在視頻的時(shí)間位置
    [compositionVideoTrack insertTimeRange:videoTimeRange ofTrack:([videoAsset tracksWithMediaType:AVMediaTypeVideo].count>0) ? [videoAsset tracksWithMediaType:AVMediaTypeVideo].firstObject : nil atTime:kCMTimeZero error:nil];
    
    
    //視頻聲音采集(也可不執(zhí)行這段代碼不采集視頻音軌，合并后的視頻文件將沒有視頻原來的聲音)
    
    AVMutableCompositionTrack *compositionVoiceTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
    
    [compositionVoiceTrack insertTimeRange:videoTimeRange ofTrack:([videoAsset tracksWithMediaType:AVMediaTypeAudio].count>0)?[videoAsset tracksWithMediaType:AVMediaTypeAudio].firstObject:nil atTime:kCMTimeZero error:nil];
    
    //聲音長(zhǎng)度截取范圍==視頻長(zhǎng)度
    CMTimeRange audioTimeRange = CMTimeRangeMake(kCMTimeZero, videoDuration);
    
    //音頻采集compositionCommentaryTrack
    AVMutableCompositionTrack *compositionAudioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
    
    [compositionAudioTrack insertTimeRange:audioTimeRange ofTrack:([audioAsset tracksWithMediaType:AVMediaTypeAudio].count > 0) ? [audioAsset tracksWithMediaType:AVMediaTypeAudio].firstObject : nil atTime:kCMTimeZero error:nil];
    
    //AVAssetExportSession用于合并文件，導(dǎo)出合并后文件，presetName文件的輸出類型
    AVAssetExportSession *assetExportSession = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetPassthrough];
    
    
    //混合后的視頻輸出路徑
    NSURL *outPutURL = [NSURL fileURLWithPath:outPath];
    
    if ([[NSFileManager defaultManager] fileExistsAtPath:outPath])
    {
        [[NSFileManager defaultManager] removeItemAtPath:outPath error:nil];
    }
    
    //輸出視頻格式 outputFileType:mov或mp4及其它視頻格式
    assetExportSession.outputFileType = outputFileType;
    assetExportSession.outputURL = outPutURL;
    //輸出文件是否網(wǎng)絡(luò)優(yōu)化
    assetExportSession.shouldOptimizeForNetworkUse = YES;
    [assetExportSession exportAsynchronouslyWithCompletionHandler:^{
        
        dispatch_async(dispatch_get_main_queue(), ^{
            
            switch (assetExportSession.status) {
                case AVAssetExportSessionStatusFailed:
                    
                    if (_interceptBlock) {
                        
                        _interceptBlock(assetExportSession.error,outPutURL);
                    }
                    
                    
                    break;
                    
                case AVAssetExportSessionStatusCancelled:{
                    
                    logdebug(@"Export Status: Cancell");
                    
                    break;
                }
                case AVAssetExportSessionStatusCompleted: {
                    
                    if (_interceptBlock) {
                        
                        _interceptBlock(nil,outPutURL);
                    }
                    
                    break;
                }
                case AVAssetExportSessionStatusUnknown: {
                    
                    logdebug(@"Export Status: Unknown");
                }
                case AVAssetExportSessionStatusExporting : {
                    
                    logdebug(@"Export Status: Exporting");
                }
                case AVAssetExportSessionStatusWaiting: {
                    
                    logdebug(@"Export Status: Wating");
                }
                    
                    
            }
            
            
        });
        
        
    }];
}

第二步：本地視頻生成GIF圖

 #pragma mark--制作GIF
/** 
@param videoURL 視頻的路徑URL
 @param loopCount 播放次數(shù) 0即無限循環(huán) 
 @param time 每幀的時(shí)間間隔 默認(rèn)0.25s
 @param imagePath 存放GIF圖片的文件路徑
 @param completeBlock 完成的回調(diào)
*/
- (void)createGIFfromURL:(NSURL*)videoURL loopCount:(int)loopCount delayTime:(CGFloat )time gifImagePath:(NSString *)imagePath complete:(CompleteBlock)completeBlock {
    
     _completeBlock =completeBlock;
    

    float delayTime = time?:0.25;
    
    // Create properties dictionaries
    NSDictionary *fileProperties = [self filePropertiesWithLoopCount:loopCount];
    NSDictionary *frameProperties = [self framePropertiesWithDelayTime:delayTime];
    
    AVURLAsset *asset = [AVURLAsset assetWithURL:videoURL];
    
    float videoWidth = [[[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] naturalSize].width;
    float videoHeight = [[[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] naturalSize].height;
    
    GIFSize optimalSize = GIFSizeMedium;
    if (videoWidth >= 1200 || videoHeight >= 1200)
        optimalSize = GIFSizeVeryLow;
    else if (videoWidth >= 800 || videoHeight >= 800)
        optimalSize = GIFSizeLow;
    else if (videoWidth >= 400 || videoHeight >= 400)
        optimalSize = GIFSizeMedium;
    else if (videoWidth < 400|| videoHeight < 400)
        optimalSize = GIFSizeHigh;
    
    // Get the length of the video in seconds
    float videoLength = (float)asset.duration.value/asset.duration.timescale;
    int framesPerSecond = 4;
    int frameCount = videoLength*framesPerSecond;
    
    // How far along the video track we want to move, in seconds.
    float increment = (float)videoLength/frameCount;
    
    // Add frames to the buffer
    NSMutableArray *timePoints = [NSMutableArray array];
    for (int currentFrame = 0; currentFrame<frameCount; ++currentFrame) {
        float seconds = (float)increment * currentFrame;
        CMTime time = CMTimeMakeWithSeconds(seconds, [timeInterval intValue]);
        [timePoints addObject:[NSValue valueWithCMTime:time]];
    }
    
   
    //completion block
    NSURL *gifURL = [self createGIFforTimePoints:timePoints fromURL:videoURL fileProperties:fileProperties frameProperties:frameProperties gifImagePath:imagePath frameCount:frameCount gifSize:_gifSize?:GIFSizeMedium];
    
    if (_completeBlock) {
        
        // Return GIF URL
        _completeBlock(_error,gifURL);
    }

}

經(jīng)過上面兩步，就可以生成本地的視頻和GIF圖了，存儲(chǔ)在沙盒即可。貼上兩步所用到的方法：

#pragma mark - Base methods

- (NSURL *)createGIFforTimePoints:(NSArray *)timePoints fromURL:(NSURL *)url fileProperties:(NSDictionary *)fileProperties  frameProperties:(NSDictionary *)frameProperties gifImagePath:(NSString *)imagePath frameCount:(int)frameCount gifSize:(GIFSize)gifSize{
    
   NSURL *fileURL = [NSURL fileURLWithPath:imagePath];
   if (fileURL == nil)
        return nil;

    CGImageDestinationRef destination = CGImageDestinationCreateWithURL((__bridge CFURLRef)fileURL, kUTTypeGIF , frameCount, NULL);
    CGImageDestinationSetProperties(destination, (CFDictionaryRef)fileProperties);

    AVURLAsset *asset = [AVURLAsset URLAssetWithURL:url options:nil];
    AVAssetImageGenerator *generator = [AVAssetImageGenerator assetImageGeneratorWithAsset:asset];
    generator.appliesPreferredTrackTransform = YES;
    
    CMTime tol = CMTimeMakeWithSeconds([tolerance floatValue], [timeInterval intValue]);
    generator.requestedTimeToleranceBefore = tol;
    generator.requestedTimeToleranceAfter = tol;
    
    NSError *error = nil;
    CGImageRef previousImageRefCopy = nil;
    for (NSValue *time in timePoints) {
        CGImageRef imageRef;
        
        #if TARGET_OS_IPHONE || TARGET_IPHONE_SIMULATOR
            imageRef = (float)gifSize/10 != 1 ? createImageWithScale([generator copyCGImageAtTime:[time CMTimeValue] actualTime:nil error:&error], (float)gifSize/10) : [generator copyCGImageAtTime:[time CMTimeValue] actualTime:nil error:&error];
        #elif TARGET_OS_MAC
            imageRef = [generator copyCGImageAtTime:[time CMTimeValue] actualTime:nil error:&error];
        #endif
        
        if (error) {
            
            _error =error;
            logdebug(@"Error copying image: %@", error);
            return nil;
            
        }
        if (imageRef) {
            CGImageRelease(previousImageRefCopy);
            previousImageRefCopy = CGImageCreateCopy(imageRef);
        } else if (previousImageRefCopy) {
            imageRef = CGImageCreateCopy(previousImageRefCopy);
        } else {
            
            _error =[NSError errorWithDomain:NSStringFromClass([self class]) code:0 userInfo:@{NSLocalizedDescriptionKey:@"Error copying image and no previous frames to duplicate"}];
            logdebug(@"Error copying image and no previous frames to duplicate");
            return nil;
        }
        CGImageDestinationAddImage(destination, imageRef, (CFDictionaryRef)frameProperties);
        CGImageRelease(imageRef);
    }
    CGImageRelease(previousImageRefCopy);
    
    // Finalize the GIF
    if (!CGImageDestinationFinalize(destination)) {
        
        _error =error;
        
        logdebug(@"Failed to finalize GIF destination: %@", error);
        if (destination != nil) {
            CFRelease(destination);
        }
        return nil;
    }
    CFRelease(destination);
    
    return fileURL;
}

#pragma mark - Helpers

CGImageRef createImageWithScale(CGImageRef imageRef, float scale) {
    
    #if TARGET_OS_IPHONE || TARGET_IPHONE_SIMULATOR
    CGSize newSize = CGSizeMake(CGImageGetWidth(imageRef)*scale, CGImageGetHeight(imageRef)*scale);
    CGRect newRect = CGRectIntegral(CGRectMake(0, 0, newSize.width, newSize.height));
    
    UIGraphicsBeginImageContextWithOptions(newSize, NO, 0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    if (!context) {
        return nil;
    }
    
    // Set the quality level to use when rescaling
    CGContextSetInterpolationQuality(context, kCGInterpolationHigh);
    CGAffineTransform flipVertical = CGAffineTransformMake(1, 0, 0, -1, 0, newSize.height);
    
    CGContextConcatCTM(context, flipVertical);
    // Draw into the context; this scales the image
    CGContextDrawImage(context, newRect, imageRef);
    
    //Release old image
    CFRelease(imageRef);
    // Get the resized image from the context and a UIImage
    imageRef = CGBitmapContextCreateImage(context);
    
    UIGraphicsEndImageContext();
    #endif
    
    return imageRef;
}

#pragma mark - Properties

- (NSDictionary *)filePropertiesWithLoopCount:(int)loopCount {
    return @{(NSString *)kCGImagePropertyGIFDictionary:
                @{(NSString *)kCGImagePropertyGIFLoopCount: @(loopCount)}
             };
}

- (NSDictionary *)framePropertiesWithDelayTime:(float)delayTime {

    return @{(NSString *)kCGImagePropertyGIFDictionary:
                @{(NSString *)kCGImagePropertyGIFDelayTime: @(delayTime)},
                (NSString *)kCGImagePropertyColorModel:(NSString *)kCGImagePropertyColorModelRGB
            };
}

最后，截取的本地視頻可用AVPlayer播放，生成的GIF圖則用UIWebView或者WKWebView又或者YYImage加載即可。