我仍在学习 AVFoundation，所以我不确定我应该如何最好地解决需要捕获高质量静止图像但提供低质量预览视频流的问题。
我有一个需要拍摄高质量图像（AVCaptureSessionPresetPhoto）的应用程序，但使用 OpenCV 处理预览视频流 - 可以接受低得多的分辨率。简单地使用基本的OpenCV Video Camera 类是不好的，因为设置defaultAVCaptureSessionPresettoAVCaptureSessionPresetPhoto会导致传递全分辨率帧processImage- 这确实非常慢。
如何与可用于捕获静止图像的设备进行高质量连接，以及可处理和显示的低质量连接？对我需要如何设置会话/连接的描述将非常有帮助。是否有此类应用程序的开源示例？
我做了类似的事情——我在委托方法中抓取了像素，用它们制作了一个 CGImageRef，然后将其发送到正常的优先级队列，在那里进行了修改。由于 AVFoundation 必须将 CADisplayLink 用于回调方法，因此它具有最高优先级。在我的特殊情况下，我没有抓取所有像素，因此它可以在 iPhone 4 上以 30fps 的速度运行。根据您要运行的设备，您可以在像素数、fps 等方面进行权衡。
另一个想法是获取 2 个像素子集的幂 - 例如，每行中的每 4 个和每 4 行。我再次在我的应用程序中以 20-30fps 的速度做了类似的事情。然后，您可以在分派的块中进一步操作这个较小的图像。
如果这看起来令人生畏，请为工作代码提供赏金。
代码：
// Image is oriented with bottle neck to the left and the bottle bottom on the right
- (void)captureOutput:(AVCaptureVideoDataOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
#if 1
AVCaptureDevice *camera = [(AVCaptureDeviceInput *)[captureSession.inputs lastObject] device];
if(camera.adjustingWhiteBalance || camera.adjustingExposure) NSLog(@"GOTCHA: %d %d", camera.adjustingWhiteBalance, camera.adjustingExposure);
printf("foo\n");
#endif
if(saveState != saveOne && saveState != saveAll) return;
@autoreleasepool {
CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
//NSLog(@"PE: value=%lld timeScale=%d flags=%x", prStamp.value, prStamp.timescale, prStamp.flags);
/*Lock the image buffer*/
CVPixelBufferLockBaseAddress(imageBuffer,0);
NSRange captureRange;
if(saveState == saveOne) {
#if 0 // B G R A MODE !
NSLog(@"PIXEL_TYPE: 0x%lx", CVPixelBufferGetPixelFormatType(imageBuffer));
uint8_t *newPtr = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer);
NSLog(@"ONE VAL %x %x %x %x", newPtr[0], newPtr[1], newPtr[2], newPtr[3]);
}
exit(0);
#endif
[edgeFinder setupImageBuffer:imageBuffer];
BOOL success = [edgeFinder delineate:1];
if(!success) {
dispatch_async(dispatch_get_main_queue(), ^{ edgeFinder = nil; [delegate error]; });
saveState = saveNone;
} else
bottleRange = edgeFinder.sides;
xRange.location = edgeFinder.shoulder;
xRange.length = edgeFinder.bottom - xRange.location;
NSLog(@"bottleRange 1: %@ neck=%d bottom=%d", NSStringFromRange(bottleRange), edgeFinder.shoulder, edgeFinder.bottom );
//searchRows = [edgeFinder expandRange:bottleRange];
rowsPerSwath = lrintf((bottleRange.length*NUM_DEGREES_TO_GRAB)*(float)M_PI/360.0f);
NSLog(@"rowsPerSwath = %d", rowsPerSwath);
saveState = saveIdling;
captureRange = NSMakeRange(0, [WLIPBase numRows]);
dispatch_async(dispatch_get_main_queue(), ^
{
[delegate focusDone];
edgeFinder = nil;
captureOutput.alwaysDiscardsLateVideoFrames = YES;
});
} else {
NSInteger rows = rowsPerSwath;
NSInteger newOffset = bottleRange.length - rows;
if(newOffset & 1) {
--newOffset;
++rows;
}
captureRange = NSMakeRange(bottleRange.location + newOffset/2, rows);
}
//NSLog(@"captureRange=%u %u", captureRange.location, captureRange.length);
/*Get information about the image*/
uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer);
size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
size_t width = CVPixelBufferGetWidth(imageBuffer);
// Note Apple sample code cheats big time - the phone is big endian so this reverses the "apparent" order of bytes
CGContextRef newContext = CGBitmapContextCreate(NULL, width, captureRange.length, 8, bytesPerRow, colorSpace, kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Little); // Video in ARGB format
assert(newContext);
uint8_t *newPtr = (uint8_t *)CGBitmapContextGetData(newContext);
size_t offset = captureRange.location * bytesPerRow;
memcpy(newPtr, baseAddress + offset, captureRange.length * bytesPerRow);
CVPixelBufferUnlockBaseAddress(imageBuffer, 0);
OSAtomicIncrement32(&totalImages);
int32_t curDepth = OSAtomicIncrement32(&queueDepth);
if(curDepth > maxDepth) maxDepth = curDepth;
#define kImageContext @"kImageContext"
#define kState @"kState"
#define kPresTime @"kPresTime"
CMTime prStamp = CMSampleBufferGetPresentationTimeStamp(sampleBuffer); // when it was taken?
//CMTime deStamp = CMSampleBufferGetDecodeTimeStamp(sampleBuffer); // now?
NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:
[NSValue valueWithBytes:&saveState objCType:@encode(saveImages)], kState,
[NSValue valueWithNonretainedObject:(__bridge id)newContext], kImageContext,
[NSValue valueWithBytes:&prStamp objCType:@encode(CMTime)], kPresTime,
nil ];
dispatch_async(imageQueue, ^
{
// could be on any thread now
OSAtomicDecrement32(&queueDepth);
if(!isCancelled) {
saveImages state; [(NSValue *)[dict objectForKey:kState] getValue:&state];
CGContextRef context; [(NSValue *)[dict objectForKey:kImageContext] getValue:&context];
CMTime stamp; [(NSValue *)[dict objectForKey:kPresTime] getValue:&stamp];
CGImageRef newImageRef = CGBitmapContextCreateImage(context);
CGContextRelease(context);
UIImageOrientation orient = state == saveOne ? UIImageOrientationLeft : UIImageOrientationUp;
UIImage *image = [UIImage imageWithCGImage:newImageRef scale:1.0 orientation:orient]; // imageWithCGImage: UIImageOrientationUp UIImageOrientationLeft
CGImageRelease(newImageRef);
NSData *data = UIImagePNGRepresentation(image);
// NSLog(@"STATE:[%d]: value=%lld timeScale=%d flags=%x", state, stamp.value, stamp.timescale, stamp.flags);
{
NSString *name = [NSString stringWithFormat:@"%d.png", num];
NSString *path = [[wlAppDelegate snippetsDirectory] stringByAppendingPathComponent:name];
BOOL ret = [data writeToFile:path atomically:NO];
//NSLog(@"WROTE %d err=%d w/time %f path:%@", num, ret, (double)stamp.value/(double)stamp.timescale, path);
if(!ret) {
++errors;
} else {
dispatch_async(dispatch_get_main_queue(), ^
{
if(num) [delegate progress:(CGFloat)num/(CGFloat)(MORE_THAN_ONE_REV * SNAPS_PER_SEC) file:path];
} );
}
++num;
}
} else NSLog(@"CANCELLED");
} );
}
}
在 AVCaptureSessionPresetPhoto 中，它使用小视频预览（iPhone6 大约 1000x700）和高分辨率照片（大约 3000x2000）。
所以我使用修改后的'CvPhotoCamera'类来处理小预览并拍摄全尺寸照片。我在这里发布此代码：https ://stackoverflow.com/a/31478505/1994445