Refering to https://github.com/MorganLu/Gstreamer/blob/master/pipeline.png:
Does it work without the outputselector and with just matroskamux ! fakesink ? If yes, the problem is that the pipeline won't preroll unless *all* sinks have received a buffer, which is not going to happen because of the output selector. Solution: set the sync that will not receive any buffers at the beginning to async=false.

Thanks for your reply, and I tried the case you suggested.
It still not works when apply audio and video to matroskamux,
when you set state of it(play->ready->play).

Further information:

If running program with --gst-debug-level=5, 
program will stuck at gst_element_set_state(muxElnt, GST_STATE_READY);
and the last line of debug message is "stopping collect pads"

Is this situation meaning that there is a bug of matroskamux when apply both audio and video streams?

Thanks for your reply, and I tried the case you suggested.
It still not works when apply audio and video to matroskamux,
when you set state of it(play->ready->play).

Further information:

If running program with --gst-debug-level=5, 
program will stuck at gst_element_set_state(muxElnt, GST_STATE_READY);
and the last line of debug message is "stopping collect pads"

Is this situation meaning that there is a bug of matroskamux when apply both audio and video streams?

Could you please provide a minimal example that just shows the problem without any changes that have to be made to the code, or interaction by the user?

morgan: Please answer comment 4.

Closing this bug report as no further information has been provided. Please feel free to reopen this bug report if you can provide the information that was asked for in a previous comment.
Thanks!