一.前言
在iOS音视频开发中，经常会看到CVPixelBufferRef这个数据结构，和ffmpeg中的AVFrame类似，里面保存着原始的图像数据。
我们发现，在有些场景中将CVPixelBufferRef送入滤镜sdk处理后，并不需要返回sdk处理后CVPixelBufferRef，就能实现滤镜效果显示的改变，如下图场景。
CVPixelBuffer使用场景
1.滤镜sdk处理CVPixelBufferRef的操作为同步操作。
2.滤镜sdk外部和内部的CVPixelBufferRef共享同一块内存。
二.实现的流程图
流程图.png
1.输入原始
CVPixelBufferRef，放到GPUImage的滤镜链中处理，输出处理后的纹理A。2.使用原始
CVPixelBufferRef生成纹理B并挂载到frame buffer object的纹理附件中。3.将
纹理A绘制到frame buffer object上，会更新纹理B的内容，进而更新CVPixelBufferRef的图像数据。4.输出滤镜处理后的
CVPixelBufferRef，其内存地址和原始的CVPixelBufferRef相同。
三.关键代码
1.使用CVPixelBufferRef创建纹理对象的两种方法：
CoreVideo框架的方法：使用此方法可以创建CVOpenGLESTextureRef纹理，并通过CVOpenGLESTextureGetName(texture)获取纹理id。
- (GLuint)convertRGBPixelBufferToTexture:(CVPixelBufferRef)pixelBuffer {
if (!pixelBuffer) {
return 0;
}
CGSize textureSize = CGSizeMake(CVPixelBufferGetWidth(pixelBuffer),
CVPixelBufferGetHeight(pixelBuffer));
CVOpenGLESTextureRef texture = nil;
CVReturn status = CVOpenGLESTextureCacheCreateTextureFromImage(nil,
[[GPUImageContext sharedImageProcessingContext] coreVideoTextureCache],
pixelBuffer,
nil,
GL_TEXTURE_2D,
GL_RGBA,
textureSize.width,
textureSize.height,
GL_BGRA,
GL_UNSIGNED_BYTE,
0,
&texture);
if (status != kCVReturnSuccess) {
NSLog(@"Can't create texture");
}
self.renderTexture = texture;
return CVOpenGLESTextureGetName(texture);
}
OpenGL的方法：
创建纹理对象，使用glTexImage2D方法上传CVPixelBufferRef中图像数据data到纹理对象中。
glBindTexture(GL_TEXTURE_2D, [outputFramebuffer texture]);
glTexImage2D(GL_TEXTURE_2D, 0, _pixelFormat==GPUPixelFormatRGB ? GL_RGB : GL_RGBA, (int)uploadedImageSize.width, (int)uploadedImageSize.height, 0, (GLint)_pixelFormat, (GLenum)_pixelType, bytesToUpload);
2.demo中使用GPUImageRawDataInput作为滤镜链起点，输入CVPixelBufferRef的图像数据，使用GPUImageTextureOutput作为滤镜链终点，输出滤镜处理后的纹理id。
- (CVPixelBufferRef)renderPixelBuffer:(CVPixelBufferRef)pixelBuffer{
if (!pixelBuffer) {
return nil;
}
CVPixelBufferRetain(pixelBuffer);
runSynchronouslyOnVideoProcessingQueue(^{
[GPUImageContext useImageProcessingContext];
CGSize size = CGSizeMake(CVPixelBufferGetWidth(pixelBuffer),
CVPixelBufferGetHeight(pixelBuffer));
CVPixelBufferLockBaseAddress(pixelBuffer, 0);
void *bytes = CVPixelBufferGetBaseAddress(pixelBuffer);
[self.dataInput updateDataFromBytes:bytes size:size];
CVPixelBufferUnlockBaseAddress(pixelBuffer, 0);
[self.dataInput processData];
GLuint textureId = self.textureOutput.texture;
[self convertTextureId:textureId textureSize:size pixelBuffer:pixelBuffer];
});
CVPixelBufferRelease(pixelBuffer);
return pixelBuffer;
}
- (void)newFrameReadyFromTextureOutput:(GPUImageTextureOutput *)callbackTextureOutput{
[self.textureOutput doneWithTexture];
}
3.使用原始CVPixelBufferRef创建纹理，将此纹理作为附件挂载到frame buffer object的纹理附件上。绘制滤镜处理后的纹理到帧缓冲对象中。
- (CVPixelBufferRef)convertTextureId:(GLuint)textureId
textureSize:(CGSize)textureSize
pixelBuffer:(CVPixelBufferRef)pixelBuffer{
[GPUImageContext useImageProcessingContext];
[self cleanUpTextures];
GLuint frameBuffer;
glGenFramebuffers(1, &frameBuffer);
glBindFramebuffer(GL_FRAMEBUFFER, frameBuffer);
// texture
GLuint targetTextureID = [self convertRGBPixelBufferToTexture:pixelBuffer];
glBindTexture(GL_TEXTURE_2D, targetTextureID);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, textureSize.width, textureSize.height, 0, GL_BGRA, GL_UNSIGNED_BYTE, NULL);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, targetTextureID, 0);
glViewport(0, 0, textureSize.width, textureSize.height);
[self renderTextureWithId:textureId];
glDeleteFramebuffers(1, &frameBuffer);
glBindFramebuffer(GL_FRAMEBUFFER, 0);
glFlush();
return pixelBuffer;
}
激活并绑定滤镜纹理，上传顶点坐标，纹理坐标到顶点着色器，开始绘制：
- (void)renderTextureWithId:(GLuint)textureId{
[GPUImageContext setActiveShaderProgram:self->normalProgram];
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, textureId);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glUniform1i(self->inputTextureUniform,0);
static const GLfloat squareVertices[] = {
-1.0f, -1.0f,
1.0f, -1.0f,
-1.0f, 1.0f,
1.0f, 1.0f,
};
glVertexAttribPointer(self->positionAttribute, 2, GL_FLOAT, GL_FALSE, 0, squareVertices);
glVertexAttribPointer(self->textureCoordinateAttribute, 2, GL_FLOAT, GL_FALSE, 0, [GPUImageFilter textureCoordinatesForRotation:kGPUImageNoRotation]);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
}
四.总结
了解了CVPiexlBufferRef以上特性后，在短视频sdk架构中，就可以设计出模块化，可插拔的滤镜组件。在视频采集，编辑，转码等场景中均可快速集成。
demo中也提供了两个简单的场景：
1.视频采集过程中添加滤镜：从GPUImageVideoCamera的代理方法中取出CVPixelBufferRef进行滤镜处理。
#pragma mark - GPUImageVideoCameraDelegate
- (void)willOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer
{
CVPixelBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
[[HYRenderManager shareManager] renderItemsToPixelBuffer:pixelBuffer];
}
视频采集过程中添加滤镜.png
2.视频播放过程中添加滤镜：在AVPlayer播放时，从实现了AVVideoCompositing协议的方法中取出CVPixelBufferRef进行滤镜处理。
#pragma mark - EditorCompositionInstructionDelegete
- (CVPixelBufferRef)renderPixelBuffer:(CVPixelBufferRef)pixelBuffer
{
return [[HYRenderManager shareManager] renderItemsToPixelBuffer:pixelBuffer];
}
视频播放过程中添加滤镜.png
源码
Github:Demo地址
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