Screen recording from a GLKView - objective-c

Question

I'm trying to record the screen of the user action from a GLKView, my video file is here, I have the correct length but it's show only a black screen.
I've subclassed GLKView, added a pan gesture recogniser on it, and whenever the user do something I draw points on my View (more complicated than that but you got it).
Here is how I initialise my video
NSError *error = nil;
NSURL *url = [NSURL fileURLWithPath:#"/Users/Dimillian/Documents/DEV/movie.mp4"];
[[NSFileManager defaultManager]removeItemAtURL:url error:nil];
self.assetWriter = [[AVAssetWriter alloc] initWithURL:url fileType:AVFileTypeAppleM4V error:&error];
if (error != nil)
{
NSLog(#"Error: %#", error);
}
NSMutableDictionary * outputSettings = [[NSMutableDictionary alloc] init];
[outputSettings setObject: AVVideoCodecH264 forKey: AVVideoCodecKey];
[outputSettings setObject: [NSNumber numberWithInt: 954] forKey: AVVideoWidthKey];
[outputSettings setObject: [NSNumber numberWithInt: 608] forKey: AVVideoHeightKey];
self.assetWriterVideoInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:outputSettings];
self.assetWriterVideoInput.expectsMediaDataInRealTime = YES;
// You need to use BGRA for the video in order to get realtime encoding. I use a color-swizzling shader to line up glReadPixels' normal RGBA output with the movie input's BGRA.
NSDictionary *sourcePixelBufferAttributesDictionary = [NSDictionary dictionaryWithObjectsAndKeys: [NSNumber numberWithInt:kCVPixelFormatType_32BGRA], kCVPixelBufferPixelFormatTypeKey,
[NSNumber numberWithInt:954], kCVPixelBufferWidthKey,
[NSNumber numberWithInt:608], kCVPixelBufferHeightKey,
nil];
self.assetWriterPixelBufferInput = [AVAssetWriterInputPixelBufferAdaptor assetWriterInputPixelBufferAdaptorWithAssetWriterInput:
self.assetWriterVideoInput sourcePixelBufferAttributes:sourcePixelBufferAttributesDictionary];
[self.assetWriter addInput:self.assetWriterVideoInput];
self.startTime = [NSDate date];
self.lastTime = CMTimeMakeWithSeconds([[NSDate date] timeIntervalSinceDate:self.startTime],120);
[self.assetWriter startWriting];
[self.assetWriter startSessionAtSourceTime:kCMTimeZero];
}
Now here is a short version of my recogniser
- (void)pan:(UIPanGestureRecognizer *)p {
// Prepare vertex to be added on screen according to user input
[self setNeedsDisplay];
}
Now here is my drawrect method
- (void)drawRect:(CGRect)rect
{
glClearColor(1, 1, 1, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
[effect prepareToDraw];
//removed code about vertex drawing
[self capturePixels];
}
And finally my capturePixels function
- (void)capturePixels
{
glFinish();
CVPixelBufferRef pixel_buffer = NULL;
CVReturn status = CVPixelBufferPoolCreatePixelBuffer (NULL, self.assetWriterPixelBufferInput.pixelBufferPool, &pixel_buffer);
if ((pixel_buffer == NULL) || (status != kCVReturnSuccess))
{
NSLog(#"%d", status);
NSLog(#"VIDEO FAILED");
return;
}
else
{
CVPixelBufferLockBaseAddress(pixel_buffer, 0);
glReadPixels(0, 0, 954, 608, GL_RGBA, GL_UNSIGNED_BYTE, CVPixelBufferGetBaseAddress(pixel_buffer));
}
// May need to add a check here, because if two consecutive times with the same value are added to the movie, it aborts recording
CMTime currentTime = CMTimeMakeWithSeconds([[NSDate date] timeIntervalSinceDate:self.startTime],120);
if(![self.assetWriterPixelBufferInput appendPixelBuffer:pixel_buffer withPresentationTime:currentTime])
{
NSLog(#"Problem appending pixel buffer at time: %lld", currentTime.value);
}
else
{
NSLog(#"%#", pixel_buffer);
NSLog(#"Recorded pixel buffer at time: %lld", currentTime.value);
self.lastTime = currentTime;
}
CVPixelBufferUnlockBaseAddress(pixel_buffer, 0);
CVPixelBufferRelease(pixel_buffer);
}
I have another function to close the video input.
- (void)tearDownGL
{
NSLog(#"Tear down");
[self.assetWriterVideoInput markAsFinished];
[self.assetWriter endSessionAtSourceTime:self.lastTime];
[self.assetWriter finishWritingWithCompletionHandler:^{
NSLog(#"finish video");
}];
[EAGLContext setCurrentContext:context];
glDeleteBuffers(1, &vertexBuffer);
glDeleteVertexArraysOES(1, &vertexArray);
effect = nil;
glFinish();
if ([EAGLContext currentContext] == context) {
[EAGLContext setCurrentContext:nil];
}
context = nil;
}
Which seems to works as I have no error, and at the end the video have the correct length, but it's only black...
I'm nowhere an expert in OpenGL, it's only a tiny part of my iOS application, I want to learn it, I'm doing my best, and thanks from the posts from #BradLarson (OpenGL ES 2.0 to Video on iPad/iPhone) I've been able to make progress, but I'm really stuck now.