如何将视频文件作为输入传递给 NodeJS 中的子进程并接收帧/图像作为输出？

Question

我在 OpenCV C++ 中编写了一个代码，该代码从命令行获取视频和时间戳（采用 HH:MM:SS 格式）作为输入，并检测该帧中的人脸。检测到的人脸被裁剪并写入 PNG 文件。

$ ./executable video.mp4 00:00:01

现在我想在 NodeJS 中为 executable 构建一个 Web API。我使用了child_process.spawn 和命令行参数。该应用程序运行没有任何错误，但我没有得到裁剪的图像作为输出。看来我的应用程序要么无法将输入视频传递给executable，要么无法从中读取输出。这是我的第一个 NodeJS 应用程序。这是我的代码。

/**
* app.js
* make sure to install express (npm install express)
* and place the executable beside this file
* or set executablePath to the correct path.
* run the app and open 'http://0.0.0.0:3000' in your browser.
*/

var child_process = require('child_process');
var path = require('path');
var express = require('express');
var app = express();

var executable = null;

app.get('/', function (req, res) {

const args = process.argv;
console.log(args);
//console.log(process.argv[3]);

if (process.argv.length <= 3) {
console.log("Usage: nodemon " + __filename + " <path/to/video> <HH:MM:SS>");
process.exit(-1);
}

if (executable !== null) {
  res.end('executable is already running.');
  return;
}

var executablePath = path.join(__dirname, './executable');
executable = child_process.spawn(executablePath, [process.argv[2], process.argv[3]]);

executable.on('exit', function (signal, code) {
console.log('executable exited with signal: %s and code: %d', signal, code);
executable = null;
});

res.end('Done.');
});

app.listen(3000);
console.log('Listening on port 3000');

我正在运行它

$ nodemon app.js video.mp4 00:00:01

我还需要知道如何从 API 本身传递参数 video.mp4 和 00:00:01。

Answer 1

我自己想出了解决方案。我需要在生成子进程时添加{stdio: 'inherit'} 选项。这是最终代码：

/**
* app.js
* make sure to install express (npm install express)
* and place the executable beside this file
* or set executablePath to the correct path.
* run the app and open 'localhost:3000/?vid=<path to video file>&tstamp=<timestamp in HH:MM:SS format>' in your browser.
*/

var child_process = require('child_process');
var path = require('path');
var express = require('express');
var app = express();
var fs = require('fs');

var executable = null;

app.get('/', function (req, res) {

if (executable !== null) {
res.end('executable is already running.');
return;
}

var video = req.param('vid');
var timestamp = req.param('tstamp');

var executablePath = path.join(__dirname, './executable2');

executable = child_process.spawn(executablePath, [video, timestamp], {stdio: 'inherit'});

executable.on('exit', function (signal, code) {
console.log('executable exited with signal: %s and code: %d', signal, code);
executable = null;
});

res.end('Done.');
});

app.listen(3000);
console.log('Listening on port 3000');

之后，运行应用程序

$ nodemon app.js

并在浏览器中打开以下链接

localhost:3000/?vid=<path to video file>&tstamp=<timestamp in HH:MM:SS format>

它从url本身获取视频文件和时间戳，运行应用时无需从终端提供这些参数。