ASSETWriterInput for making Video from UIImages on Iphone Issues - iphone

Question

I try the following 2 methods of appending UIImages pixelbuffer to ASSETWriterInput. Everything looks good except there's No data in the video file. What's wrong?
1 Adaptor class
AVAssetWriterInputPixelBufferAdaptor * avAdaptor = [AVAssetWriterInputPixelBufferAdaptor assetWriterInputPixelBufferAdaptorWithAssetWriterInput:writerInput sourcePixelBufferAttributes:NULL];
[avAdaptor appendPixelBufferixelBuffer withPresentationTime:CMTimeMake(1, 10)];
2 Making the
// Create sample buffer.
CMSampleBufferRef sampleBuffer = NULL;
result = CMSampleBufferCreateForImageBuffer(kCFAllocatorDef ault, pixelBuffer, true, NULL, NULL, videoInfo, &timing, &sampleBuffer);
// Ship out the frame.
NSParameterAssert(CMSampleBufferDataIsReady(sample Buffer));
NSParameterAssert([writerInput isReadyForMoreMediaData]);
BOOL success = [writerInput appendSampleBuffer:sampleBuffer];

Answer 1

I found that for some reason I needed to append the buffer more than once. The timing in this example from a test app I made might not be proper, but since it works it should give you a good idea.
+ (void)writeImageAsMovie:(UIImage*)image toPath:(NSString*)path size:(CGSize)size duration:(int)duration
{
NSError *error = nil;
AVAssetWriter *videoWriter = [[AVAssetWriter alloc] initWithURL:
[NSURL fileURLWithPath:path] fileType:AVFileTypeQuickTimeMovie
error:&error];
NSParameterAssert(videoWriter);
NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
AVVideoCodecH264, AVVideoCodecKey,
[NSNumber numberWithInt:size.width], AVVideoWidthKey,
[NSNumber numberWithInt:size.height], AVVideoHeightKey,
nil];
AVAssetWriterInput* writerInput = [[AVAssetWriterInput
assetWriterInputWithMediaType:AVMediaTypeVideo
outputSettings:videoSettings] retain];
AVAssetWriterInputPixelBufferAdaptor *adaptor = [AVAssetWriterInputPixelBufferAdaptor
assetWriterInputPixelBufferAdaptorWithAssetWriterInput:writerInput
sourcePixelBufferAttributes:nil];
NSParameterAssert(writerInput);
NSParameterAssert([videoWriter canAddInput:writerInput]);
[videoWriter addInput:writerInput];
//Start a session:
[videoWriter startWriting];
[videoWriter startSessionAtSourceTime:kCMTimeZero];
//Write samples:
CVPixelBufferRef buffer = [Utils pixelBufferFromCGImage:image.CGImage size:size];
[adaptor appendPixelBuffer:buffer withPresentationTime:kCMTimeZero];
[adaptor appendPixelBuffer:buffer withPresentationTime:CMTimeMake(duration-1, 2)];
//Finish the session:
[writerInput markAsFinished];
[videoWriter endSessionAtSourceTime:CMTimeMake(duration, 2)];
[videoWriter finishWriting];
}
This method is not required, but is used here as an example of a pixel buffer source:
+ (CVPixelBufferRef) pixelBufferFromCGImage:(CGImageRef)image size:(CGSize)size
{
NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithBool:YES], kCVPixelBufferCGImageCompatibilityKey,
[NSNumber numberWithBool:YES], kCVPixelBufferCGBitmapContextCompatibilityKey,
nil];
CVPixelBufferRef pxbuffer = NULL;
CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault, size.width,
size.height, kCVPixelFormatType_32ARGB, (CFDictionaryRef) options,
&pxbuffer);
status=status;//Added to make the stupid compiler not show a stupid warning.
NSParameterAssert(status == kCVReturnSuccess && pxbuffer != NULL);
CVPixelBufferLockBaseAddress(pxbuffer, 0);
void *pxdata = CVPixelBufferGetBaseAddress(pxbuffer);
NSParameterAssert(pxdata != NULL);
CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(pxdata, size.width,
size.height, 8, 4*size.width, rgbColorSpace,
kCGImageAlphaNoneSkipFirst);
NSParameterAssert(context);
//CGContextTranslateCTM(context, 0, CGImageGetHeight(image));
//CGContextScaleCTM(context, 1.0, -1.0);//Flip vertically to account for different origin
CGContextDrawImage(context, CGRectMake(0, 0, CGImageGetWidth(image),
CGImageGetHeight(image)), image);
CGColorSpaceRelease(rgbColorSpace);
CGContextRelease(context);
CVPixelBufferUnlockBaseAddress(pxbuffer, 0);
return pxbuffer;
}

Answer 2

I've had a bit of a problem with this code. It geave me a skewed image as a result.
Changing:
CGContextRef context = CGBitmapContextCreate(pxdata,
size.width,
size.height,
8,
4 * size.width,
rgbColorSpace,
kCGImageAlphaNoneSkipFirst);
To:
CGContextRef context = CGBitmapContextCreate(pxdata,
size.width,
size.height,
8,
CVPixelBufferGetBytesPerRow(pxbuffer),
rgbColorSpace,
kCGImageAlphaNoneSkipFirst);
helped.

Answer 3

Hold on, though the answer given by #Peter DeWeese is the direction to follow, the code has two huge issues: firstly, you need to wait while the system is ready to append a new media and secondly, you've got a great memory leak as you need to release your buffer after it was appended to the video writer.
This is true in your very case, but even more in a general case, where you want to loop in multiple frame as follows:
NSInteger i = 0;
for (; i<n; i++) {
image = allImages[i];
CVPixelBufferRef buffer = [self pixelBufferFromCGImage:image.CGImage cropFrame:frame];
// wait for more media data is ready
while (adaptor.assetWriterInput.readyForMoreMediaData == FALSE) {
NSDate *maxDate = [NSDate dateWithTimeIntervalSinceNow:0.1];
[[NSRunLoop currentRunLoop] runUntilDate:maxDate];
}
NSLog(#"Panorama: appending frame %ld out of %ld", (long)i, (long)n);
// Append data
[adaptor appendPixelBuffer:buffer withPresentationTime:CMTimeMake(i, freq)];//kCMTimeZero];
// release the buffer
CVPixelBufferRelease(buffer);
}