ffmpeg只录制6秒的视频

问题描述

我正在尝试从采集卡录制视频.当我希望程序控制ffmpeg时，我在Java中启动了一个进程，让ffmpeg运行30秒钟，然后通过向该进程发送"q"来关闭它.但是视频只有6秒长.我在代码中找不到任何错误，希望对您有所帮助

I'm trying to record a video from a capture card. As I want my program to control ffmpeg, I started a process within Java, let ffmpeg run for 30 seconds and then shut it down by sending "q" to the process. The video however is only 6 seconds long. I couldn't find anything wrong in my code and would appreciate some help

我的代码:

import java.io.*;

public class FfmpegTest {
    public static void main(String[] args) throws Exception {
        Process process = Runtime.getRuntime().exec("E:\\ffmpeg\\bin\\ffmpeg.exe -y -f dshow -i video=\"The video card\" bla.mp4");
        PrintWriter pw = new PrintWriter(process.getOutputStream(),true);

        Thread.sleep(30000);
        System.out.println("recording done");
        pw.println("q");
        Thread.sleep(2000);
    }
}

推荐答案

好，我知道了.视频只有6秒长的原因是因为ffmpeg有很多输出，在6秒后就已满.由于输出无处可去，因此它们堵塞了缓冲区，ffmpeg停止记录.

Ok I figured it out. The reason videos are only 6 seconds long was because ffmpeg has a lot of output which was full after 6 seconds. As the output didn't go anywhere, they clogged up the buffers and ffmpeg stopped to record.

要解决此问题，您可以执行以下两项操作之一:

To solve this, you can do one of two things:

1. 跨越一个新线程，该线程读取消息以清空流缓冲区
2. 使用 -loglevel quiet 禁止显示输出消息.如果您需要在信息流中查找特定的消息，这可能是不需要的

1. Span a new thread which reads the messages to empty the stream buffers
2. use -loglevel quiet to suppress output messages. This might be unwanted if you need to look for specific messages in the streams

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