writer_pool_2.m

#import "VideoMaker.h"
#import <MobileCoreServices/MobileCoreServices.h>
#import <AVFoundation/AVFoundation.h>

@implementation VideoMaker

-(void)makeVideo {
    //
    // Setup vars
    //
    dispatch_queue_attr_t qos = dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL, QOS_CLASS_USER_INITIATED, -1);;
    dispatch_queue_t recordingQueue = dispatch_queue_create("recordingQueue", qos); 
    NSError *error = nil;
    NSArray *f = [[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask];
    NSURL *u = [f firstObject];
    NSString *s = [[u absoluteString] stringByReplacingOccurrencesOfString:@"file://" withString:@"file://"];
    NSString *name = [NSString stringWithFormat:@"%i.mov", (int)[[NSDate date] timeIntervalSince1970]];
    NSString *p = [s stringByAppendingString:name];
    NSLog(@"path: %@", p);
    NSURL *outputURL = [NSURL URLWithString:p];
    
    //
    // Start process
    // 
    AVAssetWriter *assetWriter = [AVAssetWriter assetWriterWithURL:outputURL fileType:AVFileTypeQuickTimeMovie error:&error];
    NSDictionary *writerInputParams = [NSDictionary dictionaryWithObjectsAndKeys:
                                       AVVideoCodecTypeH264, AVVideoCodecKey,
                                       @(828), AVVideoWidthKey,
                                       @(1792), AVVideoHeightKey,
                                       AVVideoScalingModeResizeAspectFill, AVVideoScalingModeKey, nil];
    AVAssetWriterInput *assetWriterInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo 
                                                                              outputSettings:writerInputParams];    
    [assetWriter addInput:assetWriterInput];
    NSDictionary *bufferAttributes = [NSDictionary dictionaryWithObjectsAndKeys:
                                      [NSNumber numberWithInt:kCVPixelFormatType_32ARGB], kCVPixelBufferPixelFormatTypeKey, 
                                       @(5), kCVPixelBufferPoolMinimumBufferCountKey,
                                       @(5), kCVPixelBufferPoolAllocationThresholdKey,
                                       @(1), kCVPixelBufferPoolMaximumBufferAgeKey,nil];
    AVAssetWriterInputPixelBufferAdaptor *writerAdaptor = [AVAssetWriterInputPixelBufferAdaptor
                                                           assetWriterInputPixelBufferAdaptorWithAssetWriterInput:assetWriterInput
                                                           sourcePixelBufferAttributes:bufferAttributes];    
    [assetWriter startWriting];
    [assetWriter startSessionAtSourceTime:kCMTimeZero];
    [assetWriterInput requestMediaDataWhenReadyOnQueue:recordingQueue usingBlock:^{
        for (int i = 1; i < 200; ++i) {
            while (![assetWriterInput isReadyForMoreMediaData]) {
                [NSThread sleepForTimeInterval:0.01]; 
            }
            NSString *path = [NSString stringWithFormat:@"/Users/jontelang/Desktop/SnapperVideoDump/frames/frame_%i.jpg", i];
            UIImage *image = [[UIImage imageWithContentsOfFile:path] retain];
            CGImageRef ref = [image CGImage];
            CGImageRetain(ref);
            CVPixelBufferRef buffer = [self pixelBufferFromCGImage:ref pool:writerAdaptor.pixelBufferPool];
            CGImageRelease(ref);
            [image release];
            CMTime presentTime = CMTimeAdd(CMTimeMake(i, 60), CMTimeMake(1, 60));
            [writerAdaptor appendPixelBuffer:buffer withPresentationTime:presentTime];
            CVPixelBufferRelease(buffer);
        }
        [assetWriterInput markAsFinished];
        [assetWriter finishWritingWithCompletionHandler:^{}];
    }];
}

- (CVPixelBufferRef)pixelBufferFromCGImage:(CGImageRef)image pool:(CVPixelBufferPoolRef)pool {
    CVPixelBufferRef pxbuffer = NULL;
    CVPixelBufferPoolCreatePixelBuffer(kCFAllocatorDefault, pool, &pxbuffer);
    CVPixelBufferLockBaseAddress(pxbuffer, 0);
    void *pxdata = CVPixelBufferGetBaseAddress(pxbuffer);
    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(pxdata, 
                                                 CGImageGetWidth(image),
                                                 CGImageGetHeight(image), 
                                                 8, 
                                                 CVPixelBufferGetBytesPerRow(pxbuffer), 
                                                 rgbColorSpace,
                                                 (CGBitmapInfo)kCGImageAlphaNoneSkipFirst);
    CGContextSetInterpolationQuality(context, kCGInterpolationNone);
    CGContextDrawImage(context, CGRectMake(0, 0, CGImageGetWidth(image), CGImageGetHeight(image)), image);
    CGColorSpaceRelease(rgbColorSpace);
    CGContextRelease(context);
    CVPixelBufferUnlockBaseAddress(pxbuffer, 0);
    return pxbuffer;
}

@end