图片合成视频
其实，视频的画面就是一帧帧的图片，当帧率大于16也就是一秒钟有16张以上的图片时，人类的视觉就觉得它是连续的。所以，视频画面可以分解成图片，图片也可以合成视频画面。 AVFoundation库可以很方便的操作多媒体设备，AVAssetWriter这个类可以方便的将图像和音频写成一个完整的视频文件。代码如下：
NSArray *imageArray =@[[UIImage imageNamed:@"avatar"],[UIImage imageNamed:@"beauty_off"],[UIImage imageNamed:@"demo"],[UIImage imageNamed:@"recordBefore"],[UIImage imageNamed:@"recording"],[UIImage imageNamed:@"watermark"]];
CGSize size =CGSizeMake(720, 1280);
//设置mov路径
NSArray *paths =NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask,YES);
NSString *moviePath =[[paths objectAtIndex:0]stringByAppendingPathComponent:[NSString stringWithFormat:@"test.mov"]];
unlink([moviePath UTF8String]);
NSError *error;
// AVFoundation库来方便的操作多媒体设备，AVAssetWriter这个类可以方便的将图像和音频写成一个完整的视频文件
AVAssetWriter *videoWriter =[[AVAssetWriter alloc]initWithURL:[NSURL fileURLWithPath:moviePath] fileType:AVFileTypeQuickTimeMovie error:&error];
//设置视频的格式 编码 尺寸
NSDictionary *videoSettings =[NSDictionary dictionaryWithObjectsAndKeys:AVVideoCodecH264,AVVideoCodecKey,[NSNumber numberWithInt:size.width],AVVideoWidthKey,[NSNumber numberWithInt:size.height],AVVideoHeightKey,nil];
AVAssetWriterInput *writerInput =[AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:videoSettings];
NSDictionary*sourcePixelBufferAttributesDictionary =[NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:kCVPixelFormatType_32ARGB],kCVPixelBufferPixelFormatTypeKey,nil];
// AVAssetWriterInputPixelBufferAdaptor提供CVPixelBufferPool实例,
// 可以使用分配像素缓冲区写入输出文件。使用提供的像素为缓冲池分配通常
// 是更有效的比添加像素缓冲区分配使用一个单独的池
AVAssetWriterInputPixelBufferAdaptor *adaptor =[AVAssetWriterInputPixelBufferAdaptor assetWriterInputPixelBufferAdaptorWithAssetWriterInput:writerInput sourcePixelBufferAttributes:sourcePixelBufferAttributesDictionary];
//先判断下
if ([videoWriter canAddInput:writerInput]) {
[videoWriter addInput:writerInput];
[videoWriter startWriting];
[videoWriter startSessionAtSourceTime:kCMTimeZero];
}
__block int i=0;
[writerInput requestMediaDataWhenReadyOnQueue:dispatch_queue_create("mediaInputQueue", NULL)
usingBlock:^{
while ([writerInput isReadyForMoreMediaData]) {
if (++i>=imageArray.count*10) {
[writerInput markAsFinished];
[videoWriter finishWritingWithCompletionHandler:^{
NSLog(@"合并视频成功");
//保存到手机相册
}];
break;
}
CVPixelBufferRef buffer =NULL;
int idx =i/10;
if (idx <imageArray.count) {
buffer =(CVPixelBufferRef )[self pixelBufferFromCGImage:[imageArray[idx] CGImage] size:size];
}
if (buffer) {
if (![adaptor appendPixelBuffer:buffer withPresentationTime:CMTimeMake(i, 30)]) {
NSLog(@"合成fail");
}else{
NSLog(@"合成成功");
}
CFRelease(buffer);
}
}
}];
其中绘制buffer的方法如下：
- (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,(__bridge CFDictionaryRef) options,&pxbuffer);
NSParameterAssert(status ==kCVReturnSuccess && pxbuffer !=NULL);
CVPixelBufferLockBaseAddress(pxbuffer,0);
void *pxdata =CVPixelBufferGetBaseAddress(pxbuffer);
NSParameterAssert(pxdata !=NULL);
CGColorSpaceRef rgbColorSpace=CGColorSpaceCreateDeviceRGB();
// 当你调用这个函数的时候，Quartz创建一个位图绘制环境，也就是位图上下文。当你向上下文中绘制信息时，Quartz把你要绘制的信息作为位图数据绘制到指定的内存块。一个新的位图上下文的像素格式由三个参数决定：每个组件的位数，颜色空间，alpha选项
CGContextRef context =CGBitmapContextCreate(pxdata,size.width,size.height,8,4*size.width,rgbColorSpace,kCGImageAlphaPremultipliedFirst);
NSParameterAssert(context);
//使用CGContextDrawImage绘制图片 这里设置不正确的话 会导致视频颠倒
// 当通过CGContextDrawImage绘制图片到一个context中时，如果传入的是UIImage的CGImageRef，因为UIKit和CG坐标系y轴相反，所以图片绘制将会上下颠倒
CGContextDrawImage(context,CGRectMake(0,0,CGImageGetWidth(image),CGImageGetHeight(image)), image);
// 释放色彩空间
CGColorSpaceRelease(rgbColorSpace);
// 释放context
CGContextRelease(context);
// 解锁pixel buffer
CVPixelBufferUnlockBaseAddress(pxbuffer,0);
return pxbuffer;
}
图片压缩
两种压缩图片的方法：压缩图片质量(Quality)，压缩图片尺寸(Size)。
1.压缩图片质量
NSData *data = UIImageJPEGRepresentation(image, compression);
UIImage *resultImage = [UIImage imageWithData:data];
通过UIImage和NSData的相互转化，减小 JPEG 图片的质量来压缩图片。UIImageJPEGRepresentation::第二个参数compression 取值 0.0~1.0，值越小表示图片质量越低，图片文件自然越小。
1.2压缩图片尺寸
UIGraphicsBeginImageContext(size);
[image drawInRect:CGRectMake(0, 0, size.width, size.height)];
resultImage=UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
给定所需的图片尺寸 size，resultImage 即为原图 image 绘制为 size 大小后的图片。压缩图片质量的优点在于，尽可能保留图片清晰度，图片不会明显模糊；缺点在于，不能保证图片压缩后小于指定大小。压缩图片尺寸可以使图片小于指定大小，但会使图片明显模糊(比压缩图片质量模糊)。所以在实际运用中，可以两者结合起来使用，给UIImage添加一个分类，上代码：
-(NSData *)compressWithMaxLength:(NSUInteger)maxLength{
// Compress by quality
CGFloat compression = 1;
NSData *data = UIImageJPEGRepresentation(self, compression);
//NSLog(@"Before compressing quality, image size = %ld KB",data.length/1024);
if (data.length < maxLength) return data;
CGFloat max = 1;
CGFloat min = 0;
for (int i = 0; i < 6; ++i) {
compression = (max + min) / 2;
data = UIImageJPEGRepresentation(self, compression); //NSLog(@"Compression = %.1f", compression); //NSLog(@"In compressing quality loop, image size = %ld KB", data.length / 1024);
if (data.length < maxLength * 0.9)
{
min = compression;
} else if (data.length > maxLength) {
max = compression;
} else {
break;
}
}
//NSLog(@"After compressing quality, image size = %ld KB", data.length / 1024);
if (data.length < maxLength) return data;
UIImage *resultImage = [UIImage imageWithData:data];
// Compress by size
NSUInteger lastDataLength = 0;
while (data.length > maxLength && data.length != lastDataLength) {
lastDataLength = data.length;
CGFloat ratio = (CGFloat)maxLength / data.length; //NSLog(@"Ratio = %.1f", ratio);
CGSize size = CGSizeMake((NSUInteger)(resultImage.size.width * sqrtf(ratio)), (NSUInteger)(resultImage.size.height * sqrtf(ratio)));
// Use NSUInteger to prevent white blank UIGraphicsBeginImageContext(size);
[resultImage drawInRect:CGRectMake(0, 0, size.width, size.height)];
resultImage = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext();
data = UIImageJPEGRepresentation(resultImage, compression);
//NSLog(@"In compressing size loop, image size = %ld KB", data.length / 1024);
}
//NSLog(@"After compressing size loop, image size = %ld KB", data.length / 1024);
return data;
}
有什么问题，欢迎留言讨论。
