我正在尝试将从 OpenGL glReadPixels() 获取的 RGB 帧转换为 YUV 帧，并将 YUV 帧写入文件 (.yuv)。后来我想将其写入命名管道作为 FFMPEG 的输入，但现在我只想将其写入文件并使用 YUV 图像查看器查看图像结果。因此，暂时忽略“写入管道”。
运行我的代码后，我遇到了以下错误：
YUV Image Viewer 软件中显示的帧数始终是我在程序中声明的帧数的 1/3。当我声明 fps 为 10 时，我只能查看 3 帧。当我声明 fps 为 30 时，我只能观看 10 帧。但是，当我在文本编辑器中查看该文件时，我可以看到文件中打印了正确数量的“FRAME”一词。
这是我得到的示例输出：http://www.bobdanani.net/image.yuv http://www.bobdanani.net/image.yuv
我看不到正确的图像，只能看到一些扭曲的绿色、蓝色、黄色和黑色像素。
我读到了有关 YUV 格式的信息http://wiki.multimedia.cx/index.php?title=YUV4MPEG2 http://wiki.multimedia.cx/index.php?title=YUV4MPEG2 and http://www.fourcc.org/fccyvrgb.php#mikes_answer http://www.fourcc.org/fccyvrgb.php#mikes_answer and http://kylecordes.com/2007/pipe-ffmpeg http://kylecordes.com/2007/pipe-ffmpeg
这是我到目前为止所尝试过的。我知道这种转换方式效率相当低，以后可以优化一下。现在我只想让这种简单的方法发挥作用并正确显示图像。
int frameCounter = 1;
int windowWidth = 0, windowHeight = 0;
unsigned char *yuvBuffer;
unsigned long bufferLength = 0;
unsigned long frameLength = 0;
int fps = 10;
void display(void) {
/* clear the color buffers */
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
/* DRAW some OPENGL animation, i.e. cube, sphere, etc
.......
.......
*/
glutSwapBuffers();
if ((frameCounter % fps) == 1){
bufferLength = 0;
windowWidth = glutGet(GLUT_WINDOW_WIDTH);
windowHeight = glutGet (GLUT_WINDOW_HEIGHT);
frameLength = (long) (windowWidth * windowHeight * 1.5 * fps) + 100; // YUV 420 length (width*height*1.5) + header length
yuvBuffer = new unsigned char[frameLength];
write_yuv_frame_header();
}
write_yuv_frame();
frameCounter = (frameCounter % fps) + 1;
if ( (frameCounter % fps) == 1){
snprintf(filename, 100, "out/image-%d.yuv", seq_num);
ofstream out(filename, ios::out | ios::binary);
if(!out) {
cout << "Cannot open file.\n";
}
out.write (reinterpret_cast<char*> (yuvBuffer), bufferLength);
out.close();
bufferLength = 0;
delete[] yuvBuffer;
}
}
void write_yuv_frame_header (){
char *yuvHeader = new char[100];
sprintf (yuvHeader, "YUV4MPEG2 W%d H%d F%d:1 Ip A0:0 C420mpeg2 XYSCSS=420MPEG2\n", windowWidth, windowHeight, fps);
memcpy ((char*)yuvBuffer + bufferLength, yuvHeader, strlen(yuvHeader));
bufferLength += strlen (yuvHeader);
delete (yuvHeader);
}
void write_yuv_frame() {
int width = glutGet(GLUT_WINDOW_WIDTH);
int height = glutGet(GLUT_WINDOW_HEIGHT);
memcpy ((void*) (yuvBuffer+bufferLength), (void*) "FRAME\n", 6);
bufferLength +=6;
long length = windowWidth * windowHeight;
long yuv420FrameLength = (float)length * 1.5;
long lengthRGB = length * 3;
unsigned char *rgb = (unsigned char *) malloc(lengthRGB * sizeof(unsigned char));
unsigned char *yuvdest = (unsigned char *) malloc(yuv420FrameLength * sizeof(unsigned char));
glReadPixels(0, 0, windowWidth, windowHeight, GL_RGB, GL_UNSIGNED_BYTE, rgb);
int r, g, b, y, u, v, ypos, upos, vpos;
for (int j = 0; j < windowHeight; ++j){
for (int i = 0; i < windowWidth; ++i){
r = (int)rgb[(j * windowWidth + i) * 3 + 0];
g = (int)rgb[(j * windowWidth + i) * 3 + 1];
b = (int)rgb[(j * windowWidth + i) * 3 + 2];
y = (int)(r * 0.257 + g * 0.504 + b * 0.098) + 16;
u = (int)(r * 0.439 + g * -0.368 + b * -0.071) + 128;
v = (int)(r * -0.148 + g * -0.291 + b * 0.439 + 128);
ypos = j * windowWidth + i;
upos = (j/2) * (windowWidth/2) + i/2 + length;
vpos = (j/2) * (windowWidth/2) + i/2 + length + length/4;
yuvdest[ypos] = y;
yuvdest[upos] = u;
yuvdest[vpos] = v;
}
}
memcpy ((void*) (yuvBuffer + bufferLength), (void*)yuvdest, yuv420FrameLength);
bufferLength += yuv420FrameLength;
free (yuvdest);
free (rgb);
}
这只是非常基本的做法，稍后我可以优化转换算法。
谁能告诉我我的方法有什么问题吗？我的猜测是问题之一是 outstream.write() 调用，因为我将 unsigned char* 数据转换为 char* 数据，它可能会丢失数据精度。但如果我不将其转换为 char* 我会收到编译错误。然而，这并不能解释为什么输出帧被损坏（仅占总帧数的 1/3）。
