从 C++ 中的像素值数组创建视频

问题描述

有谁知道一种将存储在数组中的像素值序列保存到视频的方法?目前我正在使用 Cimg 来可视化一个简单的 n 体模拟，同时我可以将每次迭代保存到一个图像文件中，这非常慢.任何有关处理视频的类似库的建议将不胜感激.本质上，我只想将我创建的 Cimg 窗口中显示的内容记录到视频文件中.程序是用C++编写的，在linux上，用g++编译.

Does anyone know of a method to save a sequence of pixel values, stored in an array to a video? Currently I'm using Cimg to visualise a simple n-body simulation, whilst I can save each iteration to an image file, this is very slow. Any suggestions on a similar library for handling video would be appreciated. Essentially, I just want to record what's displayed in the Cimg window I create to a video file. The program is written in C++, on linux, compiling with g++.

事实上，我可以运行模拟并使用屏幕捕获软件记录它的运行情况，这似乎意味着这是可能的，但我想要一个更简洁的解决方案.

The fact that I can run the simulation and record it running with screen capturing software would seem to imply it's possible, but I'd like a tidier solution.

推荐答案

我今天正在玩这个，我想我会分享我的结果.您可以从 CImg 输出原始 RGB 视频，然后使用 ffmpeg 将其编码为视频，如下所示:

I was playing around doing this today, and thought I would share my results. You can output raw RGB video from CImg and then use ffmpeg to encode it up into video like this:

#include <iostream>
#include "CImg.h"

using namespace std;
using namespace cimg_library;

int main()
{
   const unsigned int width=1024;
   const unsigned int height=768;

   // Basic frame we will draw in
   CImg<unsigned char> image(width,height,1,3);

   unsigned char magenta[] = {255,0,255};

   // We are going to output 300 frames of 1024x768 RGB raw video
   // ... making a 10s long video at 30fps
   int radius=100;
   int cx=100;
   int cy=100;
   for(int frame=0;frame<300;frame++){
      // Start with black - it shows fewer stains ;-)
      image.fill(0);
      image.draw_circle(cx,cy,radius,magenta);

      // Move and re-colour circle
      cx+=2; cy++; if(magenta[1]!=255){magenta[1]++;}

      // Output to ffmpeg to make video, in planar GBR format
      // i.e. run program like this
      // ./main | ffmpeg -y -f rawvideo -pixel_format gbrp -video_size 1024x768 -i - -c:v h264 -pix_fmt yuv420p video.mov
      char* s=reinterpret_cast<char*>(image.data()+(width*height));   // Get start of G plane
      std::cout.write(s,width*height);                                // Output it
      s=reinterpret_cast<char*>(image.data()+2*(width*height));       // Get start of B plane
      std::cout.write(s,width*height);                                // Output it
      s=reinterpret_cast<char*>(image.data());                        // Get start of R plane
      std::cout.write(s,width*height);                                // Output it
   }
}

我想我不会去好莱坞，因为视频不是很令人兴奋！

I guess I won't make it to Hollywood as the video is not very exciting!

像这样运行上面的代码来制作视频:

Run the above code like this to make a video:

./main | ffmpeg -y -f rawvideo -pixel_format gbrp -video_size 1024x768 -i - -c:v h264 -pix_fmt yuv420p video.mov

注意 1

要意识到的是，CImg 以平面配置存储数据，这意味着首先是所有红色像素，然后是所有绿色像素，然后是所有蓝色像素 - 所有没有任何填充或空格.

The thing to realise is that CImg stores data in a planar configuration, which means all the red pixels first, then all the green ones directly afterwards and then all the blue ones straight after that - all without any padding or spaces.

想象一下 CImg 中的 4x4 图像(16 像素):

Imagine a 4x4 image (with 16 pixels) in CImg:

RRRRRRRRRRRRRRRR GGGGGGGGGGGGGGGG BBBBBBBBBBBBBBBB

与常规 RGB 数据不同，它会存储与以下内容相同的图像:

unlike regular RGB data, which would store the same image as:

RGB RGB RGB RGB RGB RGB RGB RGB RGB RGB RGB RGB RGB RGB RGB RGB 

因此，您可以将所有数据打乱并重新格式化并作为 -pixel_fmt rgb24 传递给 ffmpeg，或者像我一样在 中输出CImg 的平面格式并选择匹配的 -pixel_fmt gbrp(其中 p 表示 平面").您只需要以正确的 B、G、R 顺序输出平面.另请参阅注释 4.

So, you can either shuffle all the data around and reformat it and pass to ffmpeg as -pixel_fmt rgb24, or do as I did and output in CImg's planar format and choose a matching -pixel_fmt gbrp (where the p means "planar"). You just have to output the planes in the correct B,G,R order. See also Note 4.

注意事项 2

我选择做 3 个 write() ，每个颜色平面一个，为了演示的清晰起见，使用 聚集写入"会更有效. 和 writev()，所以:

I chose to do 3 write()s, one for each colour plane, for the sake of clarity of demonstration, it would be more efficient to use a "gathered write" with writev(), so this:

char* s=reinterpret_cast<char*>(image.data()+(width*height));   // Get start of G plane
std::cout.write(s,width*height);                                // Output it
s=reinterpret_cast<char*>(image.data()+2*(width*height));       // Get start of B plane
std::cout.write(s,width*height);                                // Output it
s=reinterpret_cast<char*>(image.data());                        // Get start of R plane
std::cout.write(s,width*height);  

会变成这样:

struct iovec iov[3];
ssize_t nwritten;

iov[0].iov_base = reinterpret_cast<char*>(image.data()+(width*height))
iov[0].iov_len  = width*height;
iov[1].iov_base = reinterpret_cast<char*>(image.data()+2*(width*height));
iov[1].iov_len  = width*height;
iov[2].iov_base = reinterpret_cast<char*>(image.data());  
iov[2].iov_len  = width*height;

nwritten = writev(STDOUT_FILENO,iov,3);

注意 3

我使用 -c:v h264 -pix_fmt yuv420p 使视频与 Mac 上的 Apple QuickTime 兼容，但无论如何您都可以轻松更改输出 -更难的部分是让 CImg 和 fmpeg 之间的接口正确.

I used the -c:v h264 -pix_fmt yuv420p to make the video compatible with Apple's QuickTime on my Mac, but you can change the output easily anyway - the harder part was getting the interface between CImg and fmpeg right.

注意事项 4

如果你想打乱数据并将其写入ffmpeg非平面(-pixel_fmt rgb)，我最初是这样做的，代码是这样的:

If you want to shuffle the data around and write it to ffmpeg non-planar (-pixel_fmt rgb), I did that originally and the code was like this:

// Outside main loop
unsigned char* BIP = new unsigned char[width*height*3];
unsigned char *d,*r,*g,*b;

...
...

// Now output it...
// ... remember CImg is band-interleaved by plane  RRRRRR GGGGGG BBBBBB
// ... not band-interleaved by pixel RGB RGB RGB RGB
r=image.data();       // Start of R plane in CImg image
g=r+(width*height);   // Start of G plane in CImg image
b=g+(width*height);   // Start of B plane in CImg image
d=BIP;                // Destination buffer in RGB order
for(int i=0;i<width*height;i++){
   *d++=*r++;
   *d++=*g++;
   *d++=*b++;
}
// Output to ffmpeg to make video, i.e. run program like this
// ./main | ffmpeg -y -f rawvideo -pixel_format rgb24 -video_size 1024x768 -i - -c:v h264 -pix_fmt yuv420p video.mov
std::cout.write(reinterpret_cast<char*>(BIP),width*height*3);

理论上，您可以使用 CImg 的 permute_axes() 方法来做到这一点，但我没有成功.

In theory, you can do this with CImg's permute_axes() method, but I had no success.

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