我服了，使用 Java 和 Python 运行 ffmpeg 命令， Java 运行了大半天不出结果， Python 秒出

This topic created in 2057 days ago, the information mentioned may be changed or developed.

大佬们，能不能说一下为什么这样啊 java

public class TestApp {
    public static void main(String[] args) throws IOException, InterruptedException {
        ProcessBuilder processBuilder = new ProcessBuilder("D:\\ffmpeg\\bin\\ffmpeg.exe", "-i", "D:\\test\\test.mp4",
                "-strict", "-2", "-vf", "crop=280:360:0:0", "D:\\test\\out.mp4"
        );
        Process process = processBuilder.start();
        process.waitFor();
    }
}

python

os.system("D:\\ffmpeg\\bin\\ffmpeg.exe -i D:\\test\\test.mp4 -strict -2 -vf crop=280:360:0:0 D:\\test\\out.mp4")

Supplement 1 · Oct 18, 2020

问题解决了, 设置 redirectErrorStream(true)，然后再从 inputstream 不断读就行了

```
package priv.sunmd.app

import java.io.BufferedReader
import java.io.IOException
import java.io.InputStream
import java.io.InputStreamReader

object TestC {
@Throws(IOException::class, InterruptedException::class)
@JvmStatic
fun main(args: Array<String>) {
val processBuilder = ProcessBuilder(
"D:\\ffmpeg\\bin\\ffmpeg.exe", "-i", "D:\\test\\test.mp4",
"-strict", "-2", "-vf", "crop=280:360:0:0", "D:\\test\\out.mp4"
)
val process = processBuilder.redirectErrorStream(true).start()

ReadStream(process.inputStream).run()
}
}

internal class ReadStream(private val inputStream: InputStream) : Runnable {
override fun run() {
val bufferedReader = BufferedReader(
InputStreamReader(inputStream)
)
try {
var line: String?
while (bufferedReader.readLine().also { line = it } != null) {
println(line)
}
} catch (e: IOException) {
e.printStackTrace()
}
}
}
```

7 replies

mayacode

Oct 18, 2020 via iPhone

把 stdout 和 stderr 读出来，也可以设置转发 err 到 stdout 然后一起读取出来，不读取如果写满缓冲会挂起程序，ffmpeg 我记得会有大量输出信息

500

Oct 18, 2020 via iPhone

没用对，说明不了问题

qwertty01

Oct 18, 2020

@xl224 大佬这样写行吗？
```
Process process = processBuilder.start();
byte[] bytes = new byte[104];
while (true) {
if (process.getInputStream().read(bytes) != -1) {
System.out.println(bytes.toString());
} else {
break;
}
}
```

lxk11153

Oct 18, 2020

-y (global)
Overwrite output files without asking.

chihiro2014

Oct 18, 2020

= =说起来，我服务端也是用 Java 调用 ffmpeg，完全没这种问题

lxk11153

Oct 18, 2020

-strict 拿来干嘛的？

----
try(InputStream pis=process.getInputStream()){
// org.apache.commons.io.IOUtils#toString(InputStream, Charset)
}

qwertty01

Oct 18, 2020

@lxk11153 不知道，我直接在网上抄的命令 😂