ProcessBuilder builder = new ProcessBuilder("myCommand");

This line of code creates an instance of the ProcessBuilder class and initializes it with the command "myCommand". This command will be used to start a new process in the operating system. The ProcessBuilder class provides a convenient way to start new processes and interact with them. Once the process is started, the program can read its output, write input to it, and wait for it to finish. The ProcessBuilder class also allows the program to set various options for the process, such as the working directory and environment variables.

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ProcessBuilder builder = new ProcessBuilder("cmd.exe", "/c", "ffmpeg");

This code creates a ProcessBuilder object that is used to run the FFmpeg command through the Windows Command Prompt (cmd.exe). The "/c" flag is used to run the command specified after it, and "ffmpeg" is the actual command being run.

Note that this code alone does not specify any arguments or options to be used with the FFmpeg command. Additional code would be needed to pass in such arguments and options.

ProcessBuilder processBuilder = new ProcessBuilder("/bin/bash", "-c", command);

ProcessBuilder 是 Java 中的一个类，它用于构建代表外部进程执行命令的对象。当你创建 `ProcessBuilder` 的实例并传入一系列参数（如 "/bin/bash" 和 "-c" 后面跟随的命令），你可以后续调用它的 start() 方法来启动一个新的操作系统进程。

在这个例子中：
- "/bin/bash" 指定了要使用的 shell，通常在 Unix 系统中它是 Bash shell。
- "-c" 是一个标志，告诉 Bash 执行紧随其后的字符串作为单条命令。
- "command" 是一个字符串，包含了实际需要执行的操作，例如运行某个脚本、执行系统命令等。

通过这种方式，Java 程序可以在安全沙箱内间接地控制和管理外部程序，而无需直接获取文件描述符或处理进程的复杂细节。比如：

String command = "ls -l";
ProcessBuilder processBuilder = new ProcessBuilder("/bin/bash", "-c", command);
try (Process process = processBuilder.start()) {
    // 读取标准输出
    BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
    String line;
    while ((line = reader.readLine()) != null) {
        System.out.println(line);
    }
}