local rtsp server video show delay 7+ seconds

[Dengke Du]

Hi all

gst-launch-1.0 --version

     gst-launch-1.0 version 1.14.2
     GStreamer 1.14.2
     Unknown package origin

My device info: v4l2-ctl --list-formats

ioctl: VIDIOC_ENUM_FMT
     Index       : 0
     Type        : Video Capture
     Pixel Format: 'YUYV'
     Name        : YUYV 4:2:2

     Index       : 1
     Type        : Video Capture
     Pixel Format: 'MJPG' (compressed)
     Name        : Motion-JPEG

Server side:

     In rtsp examples directory: ./test-launch "( v4l2src ! image/jpeg ! 
jpegdec ! x264enc ! rtph264pay name=pay0 pt=96 )"

Client side:

     gst-launch-1.0 -v playbin uri=rtsp://127.0.0.1:8554/test

The video show delay 7+ seconds, does somebody know why?

Thanks!