matroskademux: text/x-raw subtitle tracks ouputs are escaped

Submitted by Pierre Lamot

Link to original bug (#753480)

Description

Hi

when demuxing from a matroska a track encoded as S_TEXT/UTF8, the stream comes as xml escaped (< becomes < etc.)
below are sample pipeline which allow to reproduce the problem.

% gst-launch-1.0 videotestsrc is-live=true do-timestamp=true ! buffertotstxt ! text/x-raw ! identity dump=true ! matroskamux streamable=true ! filesink location=lol.mkv
Setting pipeline to PAUSED ...
Pipeline is live and does not need PREROLL ...
Setting pipeline to PLAYING ...
New clock: GstSystemClock
00000000 (0x1cb66f0): 3c 30 3a 30 30 3a 30 30 2e 30 30 35 37 38 37 35 <0:00:00.0057875
00000010 (0x1cb6700): 33 39 3e 39>
00000000 (0x7f4aa00322c0): 3c 30 3a 30 30 3a 30 30 2e 30 33 39 31 32 30 38 <0:00:00.0391208
00000010 (0x7f4aa00322d0): 37 32 3e 72>
00000000 (0x1cb66f0): 3c 30 3a 30 30 3a 30 30 2e 30 37 32 34 35 34 32 <0:00:00.0724542
00000010 (0x1cb6700): 30 35 3e 05>

% gst-launch-1.0 filesrc location=lol.mkv ! matroskaparse ! matroskademux ! text/x-raw ! fakesink dump=true
Setting pipeline to PAUSED ...
Pipeline is PREROLLING ...
Pipeline is PREROLLED ...
Setting pipeline to PLAYING ...
00000000 (0x7f6fac008510): 26 6c 74 3b 30 3a 30 30 3a 30 30 2e 30 30 35 37 <0:00:00.0057
New clock: GstSystemClock
00000010 (0x7f6fac008520): 38 37 35 33 39 26 67 74 3b 87539>
00000000 (0x7f6fac005fd0): 26 6c 74 3b 30 3a 30 30 3a 30 30 2e 30 33 39 31 <0:00:00.0391
00000010 (0x7f6fac005fe0): 32 30 38 37 32 26 67 74 3b 20872>
00000000 (0x7f6fac008510): 26 6c 74 3b 30 3a 30 30 3a 30 30 2e 30 37 32 34 <0:00:00.0724
00000010 (0x7f6fac008520): 35 34 32 30 35 26 67 74 3b 54205>

extracting the tracks with mkvextract gives the correct encoding, so I think this is rather on the demux side

% tracks lol.mkv 0:lol.srt
Extracting track 0 with the CodecID 'S_TEXT/UTF8' to the file 'lol.srt'. Container format: SRT text subtitles
Progress: 100%
% cat lol.srt
1
00:00:00,005 --> 00:00:00,038
<0:00:00.005787539>

Version: 1.4.5