Export single UIImage as movie

Question

I would like to export a single UIImage as a movie and save to disk. I have found a couple examples of creating a movie from an array of UIImage s. The closest I have got is using this code: https://github.com/HarrisonJackson/HJImagesToVideo . It's straight forward to pass an array with a single image, however I'm unsure how to modify this code to be able to set my desired movie duration. I tried to modify the CMTime with CMTimeMakeWithSeconds(5, 300) , however the exported video occasionally appears blank.

+ (void)writeImageAsMovie:(NSArray *)array
                   toPath:(NSString*)path
                     size:(CGSize)size
                      fps:(int)fps
       animateTransitions:(BOOL)shouldAnimateTransitions
        withCallbackBlock:(SuccessBlock)callbackBlock
{
    NSLog(@"%@", path);
    NSError *error = nil;
    AVAssetWriter *videoWriter = [[AVAssetWriter alloc] initWithURL:[NSURL fileURLWithPath:path]
                                                           fileType:AVFileTypeMPEG4
                                                              error:&error];
    if (error) {
        if (callbackBlock) {
            callbackBlock(NO);
        }
        return;
    }
    NSParameterAssert(videoWriter);

    NSDictionary *videoSettings = @{AVVideoCodecKey: AVVideoCodecH264,
                                    AVVideoWidthKey: [NSNumber numberWithInt:size.width],
                                    AVVideoHeightKey: [NSNumber numberWithInt:size.height]};

    AVAssetWriterInput* writerInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo
                                                                         outputSettings:videoSettings];

    AVAssetWriterInputPixelBufferAdaptor *adaptor = [AVAssetWriterInputPixelBufferAdaptor assetWriterInputPixelBufferAdaptorWithAssetWriterInput:writerInput
                                                                                                                     sourcePixelBufferAttributes:nil];
    NSParameterAssert(writerInput);
    NSParameterAssert([videoWriter canAddInput:writerInput]);
    [videoWriter addInput:writerInput];

    //Start a session:
    [videoWriter startWriting];
    [videoWriter startSessionAtSourceTime:kCMTimeZero];

    CVPixelBufferRef buffer;
    CVPixelBufferPoolCreatePixelBuffer(NULL, adaptor.pixelBufferPool, &buffer);

    CMTime presentTime = CMTimeMake(0, fps);

    int i = 0;
    while (1)
    {

        if(writerInput.readyForMoreMediaData){

            presentTime = CMTimeMake(i, fps);

            if (i >= [array count]) {
                buffer = NULL;
            } else {
                buffer = [HJImagesToVideo pixelBufferFromCGImage:[array[i] CGImage] size:CGSizeMake(480, 320)];
            }

            if (buffer) {
                //append buffer

                BOOL appendSuccess = [HJImagesToVideo appendToAdapter:adaptor
                                                          pixelBuffer:buffer
                                                               atTime:presentTime
                                                            withInput:writerInput];
                NSAssert(appendSuccess, @"Failed to append");

                if (shouldAnimateTransitions && i + 1 < array.count) {

                    //Create time each fade frame is displayed
                    CMTime fadeTime = CMTimeMake(1, fps*TransitionFrameCount);

                    //Add a delay, causing the base image to have more show time before fade begins.
                    for (int b = 0; b < FramesToWaitBeforeTransition; b++) {
                        presentTime = CMTimeAdd(presentTime, fadeTime);
                    }

                    //Adjust fadeFrameCount so that the number and curve of the fade frames and their alpha stay consistant
                    NSInteger framesToFadeCount = TransitionFrameCount - FramesToWaitBeforeTransition;

                    //Apply fade frames
                    for (double j = 1; j < framesToFadeCount; j++) {

                        buffer = [HJImagesToVideo crossFadeImage:[array[i] CGImage]
                                                         toImage:[array[i + 1] CGImage]
                                                          atSize:CGSizeMake(480, 320)
                                                       withAlpha:j/framesToFadeCount];

                        BOOL appendSuccess = [HJImagesToVideo appendToAdapter:adaptor
                                                                  pixelBuffer:buffer
                                                                       atTime:presentTime
                                                                    withInput:writerInput];
                        presentTime = CMTimeAdd(presentTime, fadeTime);

                        NSAssert(appendSuccess, @"Failed to append");
                    }
                }

                i++;
            } else {

                //Finish the session:
                [writerInput markAsFinished];

                [videoWriter finishWritingWithCompletionHandler:^{
                    NSLog(@"Successfully closed video writer");
                    if (videoWriter.status == AVAssetWriterStatusCompleted) {
                        if (callbackBlock) {
                            callbackBlock(YES);
                        }
                    } else {
                        if (callbackBlock) {
                            callbackBlock(NO);
                        }
                    }
                }];

                CVPixelBufferPoolRelease(adaptor.pixelBufferPool);

                NSLog (@"Done");
                break;
            }
        }
    }
}

+ (CVPixelBufferRef)pixelBufferFromCGImage:(CGImageRef)image
                                      size:(CGSize)imageSize
{
    NSDictionary *options = @{(id)kCVPixelBufferCGImageCompatibilityKey: @YES,
                              (id)kCVPixelBufferCGBitmapContextCompatibilityKey: @YES};
    CVPixelBufferRef pxbuffer = NULL;
    CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault, imageSize.width,
                                          imageSize.height, kCVPixelFormatType_32ARGB, (__bridge CFDictionaryRef) options,
                                          &pxbuffer);
    NSParameterAssert(status == kCVReturnSuccess && pxbuffer != NULL);

    CVPixelBufferLockBaseAddress(pxbuffer, 0);
    void *pxdata = CVPixelBufferGetBaseAddress(pxbuffer);
    NSParameterAssert(pxdata != NULL);

    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(pxdata, imageSize.width,
                                                 imageSize.height, 8, 4*imageSize.width, rgbColorSpace,
                                                 kCGImageAlphaNoneSkipFirst);
    NSParameterAssert(context);

    CGContextDrawImage(context, CGRectMake(0 + (imageSize.width-CGImageGetWidth(image))/2,
                                           (imageSize.height-CGImageGetHeight(image))/2,
                                           CGImageGetWidth(image),
                                           CGImageGetHeight(image)), image);
    CGColorSpaceRelease(rgbColorSpace);
    CGContextRelease(context);

    CVPixelBufferUnlockBaseAddress(pxbuffer, 0);

    return pxbuffer;
}

+ (CVPixelBufferRef)crossFadeImage:(CGImageRef)baseImage
                           toImage:(CGImageRef)fadeInImage
                            atSize:(CGSize)imageSize
                         withAlpha:(CGFloat)alpha
{
    NSDictionary *options = @{(id)kCVPixelBufferCGImageCompatibilityKey: @YES,
                              (id)kCVPixelBufferCGBitmapContextCompatibilityKey: @YES};
    CVPixelBufferRef pxbuffer = NULL;
    CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault, imageSize.width,
                                          imageSize.height, kCVPixelFormatType_32ARGB, (__bridge CFDictionaryRef) options,
                                          &pxbuffer);
    NSParameterAssert(status == kCVReturnSuccess && pxbuffer != NULL);

    CVPixelBufferLockBaseAddress(pxbuffer, 0);
    void *pxdata = CVPixelBufferGetBaseAddress(pxbuffer);
    NSParameterAssert(pxdata != NULL);

    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(pxdata, imageSize.width,
                                                 imageSize.height, 8, 4*imageSize.width, rgbColorSpace,
                                                 kCGImageAlphaNoneSkipFirst);
    NSParameterAssert(context);

    CGRect drawRect = CGRectMake(0 + (imageSize.width-CGImageGetWidth(baseImage))/2,
                                 (imageSize.height-CGImageGetHeight(baseImage))/2,
                                 CGImageGetWidth(baseImage),
                                 CGImageGetHeight(baseImage));

    CGContextDrawImage(context, drawRect, baseImage);

    CGContextBeginTransparencyLayer(context, nil);
    CGContextSetAlpha( context, alpha );
    CGContextDrawImage(context, drawRect, fadeInImage);
    CGContextEndTransparencyLayer(context);

    CGColorSpaceRelease(rgbColorSpace);
    CGContextRelease(context);

    CVPixelBufferUnlockBaseAddress(pxbuffer, 0);

    return pxbuffer;
}

+ (BOOL)appendToAdapter:(AVAssetWriterInputPixelBufferAdaptor*)adaptor
            pixelBuffer:(CVPixelBufferRef)buffer
                 atTime:(CMTime)presentTime
              withInput:(AVAssetWriterInput*)writerInput
{
    while (!writerInput.readyForMoreMediaData) {
        usleep(1);
    }

    return [adaptor appendPixelBuffer:buffer withPresentationTime:presentTime];
}

Answer 1

CMTimeMake(0, fps); --> You shouldn't use 0. CMTimeMake(x, y); defines the length of each frame. x/y seconds. So for example if you set CMTimeMake(1, 10), that means every image will be shown for 1/10 seconds. I think your video became blank, because you set 0 for the x, that means 0/y seconds which will be 0, so all the frames will be shown for 0 seconds... If you would like to send an exact video length you can do it like that:

desired video length divided by your image count)... Convert this to x/y format and than you got what you should enter into the CMTime.

If you would like to make a 10 second video, with 100 frames it should look like this: 10/100 = 0,1 = 1/10 sec / frame --> CMTimeMake(1,10)

If you would like to make a 30 second video, with 1000 frames it should look like this: 30/1000 = 0,03 = 3/100 sec / frame --> CMTimeMake(3,100)

I hope this helped :).