ffmpeg推流报错Failed to update header with correct duration.

[flv @ 0x21d6a00] Failed to update header with correct duration.
[flv @ 0x21d6a00] Failed to update header with correct filesize.

推流命令如下：
ffmpeg -i test_video.mp4 -c copy -f flv rtmp://127.0.0.1/live/livestream
需要加上-re
fmpeg -re -i test_video.mp4 -c copy -f flv rtmp://127.0.0.1/live/livestream
使得ffmpeg推流时根据原来视频的帧率进行，如果不设置的话就会报以上错误，因为它会以全速推流。