AVFoundation: add text to the CMSampleBufferRef video frame - ios

Question

I'm building an app using AVFoundation.
Just before I call [assetWriterInput appendSampleBuffer:sampleBuffer] in
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection-method.
I manipulate the pixels in the sample buffer (using a pixelbuffer to apply an effect).
But the client wants me to put in a text (timestamp & framecounter) as well on the frames, but I haven't found a way to do this yet.
I tried to convert the samplebuffer to an Image, apply text on the image, and convert the image back to a samplebuffer, but then
CMSampleBufferDataIsReady(sampleBuffer)
fails.
Here are my UIImage category methods:
+ (UIImage *) imageFromSampleBuffer:(CMSampleBufferRef) sampleBuffer
{
CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
CVPixelBufferLockBaseAddress(imageBuffer,0);
uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer);
size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
size_t width = CVPixelBufferGetWidth(imageBuffer);
size_t height = CVPixelBufferGetHeight(imageBuffer);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
CGImageRef newImage = CGBitmapContextCreateImage(newContext);
CGContextRelease(newContext);
CGColorSpaceRelease(colorSpace);
UIImage *newUIImage = [UIImage imageWithCGImage:newImage];
CFRelease(newImage);
return newUIImage;
}
And
- (CMSampleBufferRef) cmSampleBuffer
{
CGImageRef image = self.CGImage;
NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithBool:YES], kCVPixelBufferCGImageCompatibilityKey,
[NSNumber numberWithBool:YES], kCVPixelBufferCGBitmapContextCompatibilityKey,
nil];
CVPixelBufferRef pxbuffer = NULL;
CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault,
self.size.width,
self.size.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, self.size.width,
self.size.height, 8, 4*self.size.width, rgbColorSpace,
kCGImageAlphaNoneSkipFirst);
NSParameterAssert(context);
CGContextConcatCTM(context, CGAffineTransformMakeRotation(0));
CGContextDrawImage(context, CGRectMake(0, 0, CGImageGetWidth(image),
CGImageGetHeight(image)), image);
CGColorSpaceRelease(rgbColorSpace);
CGContextRelease(context);
CVPixelBufferUnlockBaseAddress(pxbuffer, 0);
CMVideoFormatDescriptionRef videoInfo = NULL;
CMSampleBufferRef sampleBuffer = NULL;
CMSampleBufferCreateForImageBuffer(kCFAllocatorDefault,
pxbuffer, true, NULL, NULL, videoInfo, NULL, &sampleBuffer);
return sampleBuffer;
}
Any ideas?
EDIT:
I changed my code with Tony's answer. (Thank you!)
This code works:
CVPixelBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
CVPixelBufferLockBaseAddress( pixelBuffer, 0 );
EAGLContext *eaglContext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
CIContext *ciContext = [CIContext contextWithEAGLContext:eaglContext options:#{kCIContextWorkingColorSpace : [NSNull null]} ];
UIFont *font = [UIFont fontWithName:#"Helvetica" size:40];
NSDictionary *attributes = #{NSFontAttributeName: font,
NSForegroundColorAttributeName: [UIColor lightTextColor]};
UIImage *img = [UIImage imageFromText:#"01 - 13/02/2014 15:18:21:654" withAttributes:attributes];
CIImage *filteredImage = [[CIImage alloc] initWithCGImage:img.CGImage];
[ciContext render:filteredImage toCVPixelBuffer:pixelBuffer bounds:[filteredImage extent] colorSpace:CGColorSpaceCreateDeviceRGB()];
CVPixelBufferUnlockBaseAddress(pixelBuffer, 0);

Answer 1

You should refer the CIFunHouse sample from apple, and you may use this api to draw directly to the buffer
-(void)render:(CIImage *)image toCVPixelBuffer:(CVPixelBufferRef)buffer bounds:(CGRect)r colorSpace:(CGColorSpaceRef)cs
You can download it here WWDC2013
Create the context
_eaglContext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
_ciContext = [CIContext contextWithEAGLContext:_eaglContext options:#{kCIContextWorkingColorSpace : [NSNull null]} ];
Now render the image
CVPixelBufferRef renderedOutputPixelBuffer = NULL;
OSStatus err = CVPixelBufferPoolCreatePixelBuffer(nil, self.pixelBufferAdaptor.pixelBufferPool, &renderedOutputPixelBuffer);
[_ciContext render:filteredImage toCVPixelBuffer:renderedOutputPixelBuffer bounds:[filteredImage extent]