play with ".ass" subtitle failed

[Arwen]

When I tried to play a video with an external subtitle file, the text cannot
be displayed without any error reported.
I tried to use gst-launch and get the pipeline information.
And found there was no parser element which should be connected to parse the
file.
I checked my plugin list and "ssaparse" should be used to parse x-ass
format.
But I don't why it couldn't be connected.

Is there anyone who is familiar with this problem and be kindly to provide
some suggestion?
My test subtitle file
01_AVI_subtitle.ASS
<http://gstreamer-devel.966125.n4.nabble.com/file/t378148/01_AVI_subtitle.ASS>  

gst-launch command
gst-launch-1.0  playbin uri="file:///media/sf_Projects/01_AVI_subtitle.AVI"
suburi="file:///media/sf_Projects/01_AVI_subtitle.ASS"

ssaparse information
Factory Details:
  Rank                     primary (256)
  Long-name                SSA Subtitle Parser
  Klass                    Codec/Parser/Subtitle
  Description              Parses SSA subtitle streams
  Author                   Tim-Philipp Müller <tim centricular net>

Plugin Details:
  Name                     subparse
  Description              Subtitle parsing
  Filename                
/usr/lib/x86_64-linux-gnu/gstreamer-1.0/libgstsubparse.so
  Version                  1.8.3
  License                  LGPL
  Source module            gst-plugins-base
  Source release date      2016-08-19
  Binary package           GStreamer Base Plugins (Ubuntu)
  Origin URL              
https://launchpad.net/distros/ubuntu/+source/gst-plugins-base1.0

GObject
 +----GInitiallyUnowned
       +----GstObject
             +----GstElement
                   +----GstSsaParse

Pad Templates:
  SRC template: 'src'
    Availability: Always
    Capabilities:
      text/x-raw
                 format: pango-markup

  SINK template: 'sink'
    Availability: Always
    Capabilities:
      application/x-ssa
      application/x-ass


Element Flags:
  no flags set

Element Implementation:
  Has change_state() function: gst_ssa_parse_change_state

Element has no clocking capabilities.
Element has no URI handling capabilities.

Pads:
  SINK: 'sink'
    Pad Template: 'sink'
  SRC: 'src'
    Pad Template: 'src'

Element Properties:
  name                : The name of the object
                        flags: readable, writable
                        String. Default: "ssaparse0"
  parent              : The parent of the object
                        flags: readable, writable
                        Object of type "GstObject"




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