iOS 在线视频生成GIF图功能的方法

在一些视频APP中，都可以看到一个将在线视频转成GIF图的功能。下面就来说说思路以及实现。我们知道本地视频可以生成GIF,那么将在线视频截取成本地视频不就可以了吗？经过比较，腾讯视频App也是这么做的。话不多说，下面开始上代码：

第一步：截取视频

#pragma mark -截取视频
- (void)interceptVideoAndVideoUrl:(NSURL *)videoUrl withOutPath:(NSString *)outPath outputFileType:(NSString *)outputFileType range:(NSRange)videoRange intercept:(InterceptBlock)interceptBlock {

 _interceptBlock =interceptBlock;

 //不添加背景音乐
 NSURL *audioUrl =nil;
 //AVURLAsset此类主要用于获取媒体信息，包括视频、声音等
 AVURLAsset* audioAsset = [[AVURLAsset alloc] initWithURL:audioUrl options:nil];
 AVURLAsset* videoAsset = [[AVURLAsset alloc] initWithURL:videoUrl options:nil];

 //创建AVMutableComposition对象来添加视频音频资源的AVMutableCompositionTrack
 AVMutableComposition* mixComposition = [AVMutableComposition composition];

 //CMTimeRangeMake(start, duration),start起始时间，duration时长，都是CMTime类型
 //CMTimeMake(int64_t value, int32_t timescale)，返回CMTime，value视频的一个总帧数，timescale是指每秒视频播放的帧数，视频播放速率，（value / timescale）才是视频实际的秒数时长，timescale一般情况下不改变，截取视频长度通过改变value的值
 //CMTimeMakeWithSeconds(Float64 seconds, int32_t preferredTimeScale)，返回CMTime，seconds截取时长（单位秒），preferredTimeScale每秒帧数

 //开始位置startTime
 CMTime startTime = CMTimeMakeWithSeconds(videoRange.location, videoAsset.duration.timescale);
 //截取长度videoDuration
 CMTime videoDuration = CMTimeMakeWithSeconds(videoRange.length, videoAsset.duration.timescale);

 CMTimeRange videoTimeRange = CMTimeRangeMake(startTime, videoDuration);

 //视频采集compositionVideoTrack
 AVMutableCompositionTrack *compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];

 // 避免数组越界 tracksWithMediaType 找不到对应的文件时候返回空数组
 //TimeRange截取的范围长度
 //ofTrack来源
 //atTime插放在视频的时间位置
 [compositionVideoTrack insertTimeRange:videoTimeRange ofTrack:([videoAsset tracksWithMediaType:AVMediaTypeVideo].count>0) ? [videoAsset tracksWithMediaType:AVMediaTypeVideo].firstObject : nil atTime:kCMTimeZero error:nil];

 //视频声音采集(也可不执行这段代码不采集视频音轨，合并后的视频文件将没有视频原来的声音)

 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];

 //声音长度截取范围==视频长度
 CMTimeRange audioTimeRange = CMTimeRangeMake(kCMTimeZero, videoDuration);

 //音频采集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，导出合并后文件，presetName文件的输出类型
 AVAssetExportSession *assetExportSession = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetPassthrough];

 //混合后的视频输出路径
 NSURL *outPutURL = [NSURL fileURLWithPath:outPath];

 if ([[NSFileManager defaultManager] fileExistsAtPath:outPath])
 {
  [[NSFileManager defaultManager] removeItemAtPath:outPath error:nil];
 }

 //输出视频格式
 assetExportSession.outputFileType = outputFileType;
 assetExportSession.outputURL = outPutURL;
 //输出文件是否网络优化
 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：本地视频生成GIF图

/**
 生成GIF图片
 @param videoURL 视频的路径URL
 @param loopCount 播放次数
 @param time 每帧的时间间隔 默认0.25s
 @param imagePath 存放GIF图片的文件路径
 @param completeBlock 完成的回调

 */
 #pragma mark--制作GIF
- (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);
 }

}

经过上面两步，就可以生成本地的视频和GIF图了，存储在沙盒即可。贴上两步所用到的方法：

#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，截取的本地视频可用AVPlayer播放，生成的GIF图则用UIWebView或者WKWebView又或者 YYImage 加载即可。

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