读取视频帧 iPhone 时出现内存问题

Posted 2023-03-11

【中文标题】读取视频帧 iPhone 时出现内存问题

【英文标题】：Memory Issue while reading video frames iPhone

【发布时间】：2012-03-27 10:14:47

【问题描述】：

我在从 iPhone 库中选择的现有视频中读取视频帧时出现内存问题。首先，我将 UIImage-frames 本身添加到一个数组中，但我认为一段时间后数组对于内存来说太大了，所以我将 UIImages 保存在文档文件夹中并将图像路径添加到数组中。但是，即使使用 Instruments 检查分配，我仍然会收到相同的内存警告。分配的总内存永远不会超过 2.5mb。也没有发现泄漏...有人能想到什么吗？

-(void)addFrame:(UIImage *)image

    NSString *imgPath = [NSString stringWithFormat:@"%@/Analysis%d-%d.png", docFolder, currentIndex, framesArray.count];       
    [UIImagePNGRepresentation(image) writeToFile:imgPath atomically:YES];
    [framesArray addObject:imgPath];    
    frameCount++;      


-(void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info

    [picker dismissModalViewControllerAnimated:YES];
    [framesArray removeAllObjects];    
    frameCount = 0;          

    // incoming video
    NSURL *videoURL = [info valueForKey:UIImagePickerControllerMediaURL];
    //NSLog(@"Video : %@", videoURL);

    // AVURLAsset to read input movie (i.e. mov recorded to local storage)
    NSDictionary *inputOptions = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:AVURLAssetPreferPreciseDurationAndTimingKey];
    AVURLAsset *inputAsset = [[AVURLAsset alloc] initWithURL:videoURL options:inputOptions];     

    // Load the input asset tracks information
    [inputAsset loadValuesAsynchronouslyForKeys:[NSArray arrayWithObject:@"tracks"] completionHandler: ^        

        NSError *error = nil;
        nrFrames = CMTimeGetSeconds([inputAsset duration]) * 30;
        NSLog(@"Total frames = %d", nrFrames);

        // Check status of "tracks", make sure they were loaded    
        AVKeyValueStatus tracksStatus = [inputAsset statusOfValueForKey:@"tracks" error:&error];
        if (!tracksStatus == AVKeyValueStatusLoaded)
            // failed to load
            return;        

        /* Read video samples from input asset video track */
        AVAssetReader *reader = [AVAssetReader assetReaderWithAsset:inputAsset error:&error];

        NSMutableDictionary *outputSettings = [NSMutableDictionary dictionary];
        [outputSettings setObject: [NSNumber numberWithInt:kCVPixelFormatType_32BGRA]  forKey: (NSString*)kCVPixelBufferPixelFormatTypeKey];
        AVAssetReaderTrackOutput *readerVideoTrackOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:[[inputAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] outputSettings:outputSettings];


        // Assign the tracks to the reader and start to read
        [reader addOutput:readerVideoTrackOutput];
        if ([reader startReading] == NO) 
            // Handle error
            NSLog(@"Error reading");
        

        NSAutoreleasePool *pool = [NSAutoreleasePool new];
        while (reader.status == AVAssetReaderStatusReading)
                    
            if(!memoryProblem)
            
                CMSampleBufferRef sampleBufferRef = [readerVideoTrackOutput copyNextSampleBuffer];
                if (sampleBufferRef) 
                
                    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBufferRef);
                    /*Lock the image buffer*/
                    CVPixelBufferLockBaseAddress(imageBuffer,0); 
                    /*Get information about the image*/
                    uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer); 
                    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer); 
                    size_t width = CVPixelBufferGetWidth(imageBuffer); 
                    size_t height = CVPixelBufferGetHeight(imageBuffer); 

                    /*We unlock the  image buffer*/
                    CVPixelBufferUnlockBaseAddress(imageBuffer,0);

                    /*Create a CGImageRef from the CVImageBufferRef*/
                    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); 
                    CGContextRef newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst); 
                    CGImageRef newImage = CGBitmapContextCreateImage(newContext); 

                    /*We release some components*/
                    CGContextRelease(newContext); 
                    CGColorSpaceRelease(colorSpace);

                    UIImage *image= [UIImage imageWithCGImage:newImage scale:[UIScreen mainScreen].scale orientation:UIImageOrientationRight];          
                    //[self addFrame:image];
                    [self performSelectorOnMainThread:@selector(addFrame:) withObject:image waitUntilDone:YES];

                    /*We release the CGImageRef*/
                    CGImageRelease(newImage);                    

                    CMSampleBufferInvalidate(sampleBufferRef);
                    CFRelease(sampleBufferRef);
                    sampleBufferRef = NULL;
                
            
            else 
                            
                break;
                        
        
        [pool release];

        NSLog(@"Finished");        
    ];   

【参考方案1】：

你做一件事然后尝试。

将NSAutoreleasePool 移动到while 循环内并将其排空。

所以它会是这样的：

while (reader.status == AVAssetReaderStatusReading)
            
    NSAutoreleasePool *pool = [NSAutoreleasePool new];

    .....

    [pool drain];
 

【讨论】：

你是个天才，它行得通！！！不过我想知道，你是怎么想到这个的？为什么将 autoreleasepool 放在 while 循环中时会起作用？

如果它在循环之外，那么池只会在循环结束时被排空。但在循环结束之前，内存会累积并崩溃。因此，如果它在内部，则在每次迭代时，都会释放自动释放的对象。