dashdemux: mosaic issue for MPEG DASH live streaming due to not updating headers

Submitted by WeiChungChang

Link to original bug (#777206)

Description

Created attachment 343415
issue description in detail

as https://bugzilla.gnome.org/show_bug.cgi?id=767682

original test URL is invalid but I found a one which can reproduce the issue.

Please refer to the attached in detail, or by the link below:
http://programmingmemojohnchang.blogspot.tw/2017/01/potential-race-condition-issue-of.html

I tested it for 1.4.5 (a little old) but I wonder it will happen for master also.
Please help to check it.

[Issue]:
Wrong codec settings leads to mosaic (ex, use the codec setting of high bit-rate representation to decode data of low bit-rate representation ).

[Root cause]:

1. Race condition between threads.
2. Slow start of gst_mpd_client_setup_streaming() when updating manifest.

Attachment 343415, "issue description in detail":
Potential_race_condition_issue_of_GStreamer.pdf