iOS - 逐帧读取视频文件，图像处理，然后另存为新视频文件

Question

我尝试从 iPhone 相册中逐帧读取视频。图像处理后，我会将它们保存为新视频。我运行我的代码没有任何错误，但相册中没有新视频。

这是我的代码。

// Video writer init
- (BOOL)setupAssetWriterForURL:(CMFormatDescriptionRef)formatDescription
{
    float bitsPerPixel;
    CMVideoDimensions dimensions = CMVideoFormatDescriptionGetDimensions(formatDescription);
    int numPixels = dimensions.width * dimensions.height;
    int bitsPerSecond;

    if ( numPixels < (640 * 480) )
        bitsPerPixel = 4.05; 
    else
        bitsPerPixel = 11.4; 

    bitsPerSecond = numPixels * bitsPerPixel;

    NSDictionary *videoCompressionSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                                              AVVideoCodecH264, AVVideoCodecKey,
                                              [NSNumber numberWithInteger:dimensions.width], AVVideoWidthKey,
                                              [NSNumber numberWithInteger:dimensions.height], AVVideoHeightKey,
                                              [NSDictionary dictionaryWithObjectsAndKeys:
                                               [NSNumber numberWithInteger:bitsPerSecond], AVVideoAverageBitRateKey,
                                               [NSNumber numberWithInteger:30], AVVideoMaxKeyFrameIntervalKey,
                                               nil], AVVideoCompressionPropertiesKey,
                                              nil];
    if ([assetWriter canApplyOutputSettings:videoCompressionSettings forMediaType:AVMediaTypeVideo]) {
        assetWriterVideoIn = [[AVAssetWriterInput alloc] initWithMediaType:AVMediaTypeVideo outputSettings:videoCompressionSettings];
        assetWriterVideoIn.expectsMediaDataInRealTime = YES;
        assetWriterVideoIn.transform = [self transformFromCurrentVideoOrientationToOrientation:self.referenceOrientation];
        if ([assetWriter canAddInput:assetWriterVideoIn])
            [assetWriter addInput:assetWriterVideoIn];
        else {
            NSLog(@"Couldn't add asset writer video input.");
            return NO;
        }
    }
    else {
        NSLog(@"Couldn't apply video output settings.");
        return NO;
    }

    return YES;
}

阅读视频

- (void)readMovie:(NSURL *)url
{
    AVURLAsset * asset = [AVURLAsset URLAssetWithURL:url options:nil];
    [asset loadValuesAsynchronouslyForKeys:[NSArray arrayWithObject:@"tracks"] completionHandler:
     ^{
         dispatch_async(dispatch_get_main_queue(),
                        ^{
                            AVAssetTrack * videoTrack = nil;
                            NSArray * tracks = [asset tracksWithMediaType:AVMediaTypeVideo];
                            if ([tracks count] == 1)
                            {
                                videoTrack = [tracks objectAtIndex:0];

                                NSError * error = nil;

                                // _movieReader is a member variable
                                AVAssetReader *movieReader = [[AVAssetReader alloc] initWithAsset:asset error:&error];
                                if (error)
                                    NSLog(@"_movieReader fail!\n");

                                NSString* key = (NSString*)kCVPixelBufferPixelFormatTypeKey;
                                NSNumber* value = [NSNumber numberWithUnsignedInt:kCVPixelFormatType_32BGRA];
                                NSDictionary* videoSettings = 
                                [NSDictionary dictionaryWithObject:value forKey:key]; 

                                [movieReader addOutput:[AVAssetReaderTrackOutput 
                                                         assetReaderTrackOutputWithTrack:videoTrack 
                                                         outputSettings:videoSettings]];
                                [movieReader startReading];

                                while ([movieReader status] == AVAssetReaderStatusReading)
                                {
                                    AVAssetReaderTrackOutput * output = [movieReader.outputs objectAtIndex:0];
                                    CMSampleBufferRef sampleBuffer = [output copyNextSampleBuffer];
                                    if (sampleBuffer)
                                    {
                                        if ( !assetWriter ) {
                                            outputURL = [NSURL fileURLWithPath:[NSString stringWithFormat:@"%@/%llu.mov", NSTemporaryDirectory(), mach_absolute_time()]];

                                            NSError *error = nil;
                                            assetWriter = [[AVAssetWriter alloc] initWithURL:outputURL fileType:(NSString *)kUTTypeQuickTimeMovie error:&error];
                                            if (error)
                                                [self showError:error];


                                            if (assetWriter) {
                                                CMFormatDescriptionRef formatDescription = CMSampleBufferGetFormatDescription(sampleBuffer);
                                                [self setupAssetWriterForURL:formatDescription];
                                            }
                                        }
                                        CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);


                                        CVPixelBufferLockBaseAddress(imageBuffer,0);

                                        int bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
                                        int bufferWidth = CVPixelBufferGetWidth(imageBuffer);
                                        int bufferHeight = CVPixelBufferGetHeight(imageBuffer);
                                        unsigned char *pixel = (unsigned char *)CVPixelBufferGetBaseAddress(imageBuffer);


                                        for( int row = 0; row < bufferHeight; row++ ) {
                                            for( int column = 0; column < bufferWidth; column++ ) {

                                                pixel[0] = (pixel[0]+pixel[1]+pixel[2])/3;
                                                pixel[1] = (pixel[0]+pixel[1]+pixel[2])/3;
                                                pixel[2] = (pixel[0]+pixel[1]+pixel[2])/3;

                                                pixel += 4;
                                            }
                                        }


                                        CVPixelBufferUnlockBaseAddress(imageBuffer,0);

                                        if ( assetWriter ) {
                                            [self writeSampleBuffer:sampleBuffer ofType:AVMediaTypeVideo];
                                        }


                                        CFRelease(sampleBuffer);
                                    }

                                }
                                if (assetWriter) {
                                    [assetWriterVideoIn markAsFinished];
                                    assetWriter = nil;
                                    [assetWriter finishWriting];
                                    assetWriterVideoIn = nil;
                                    assetWriter = nil;

                                    [self saveMovieToCameraRoll];
                                }
                                else {
                                    [self showError:[assetWriter error]];
                                }

                            }
                        });
     }];

}
- (void) writeSampleBuffer:(CMSampleBufferRef)sampleBuffer ofType:(NSString *)mediaType
{
    if ( assetWriter.status == AVAssetWriterStatusUnknown ) {

        if ([assetWriter startWriting]) {
            [assetWriter startSessionAtSourceTime:CMSampleBufferGetPresentationTimeStamp(sampleBuffer)];
        }
        else {
            [self showError:[assetWriter error]];
        }
    }

    if ( assetWriter.status == AVAssetWriterStatusWriting ) {

        if (mediaType == AVMediaTypeVideo) {
            if (assetWriterVideoIn.readyForMoreMediaData) {
                if (![assetWriterVideoIn appendSampleBuffer:sampleBuffer]) {
                    [self showError:[assetWriter error]];
                }
            }
        }

    }
}
- (void)saveMovieToCameraRoll
{
    ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
    [library writeVideoAtPathToSavedPhotosAlbum:outputURL
                                completionBlock:^(NSURL *assetURL, NSError *error) {
                                    if (error){
                                        [self showError:error];
                                    NSLog(@"save fail");
                                }
                                    else
                                    {
                                        [self removeFile:outputURL];
                                        NSLog(@"!!!");
                                    }
                                    });
                                }];
}
- (void)removeFile:(NSURL *)fileURL
{
    NSFileManager *fileManager = [NSFileManager defaultManager];
    NSString *filePath = [fileURL path];
    if ([fileManager fileExistsAtPath:filePath]) {
        NSError *error;
        BOOL success = [fileManager removeItemAtPath:filePath error:&error];
        if (!success)
            [self showError:error];
    }
}

有什么建议吗？

Answer 1

我有点晚了，但它可能对其他人有帮助，代码几乎是正确的，但只需注释一行代码即可，它在 readMovie: 方法中

                            //assetWriter = nil; commented line  
                               [assetWriter finishWriting];
                                assetWriterVideoIn = nil;
                                assetWriter = nil;

                                [self saveMovieToCameraRoll];
                            }`