确保您在代码中使用的确切命令可以从命令行工作。看来对于管道，格式和编解码器必须手动指定：

First make sure the exact command you use in the code works from the command line. It appears that for pipes the format and codec must be specified manually:

ffmpeg -f image2pipe -codec mjpeg -i pipe:0 out.avi < input.jpg

Java程序本身看起来不错。

The Java program itself looks fine.