Qt 5.3.2: cannot play HTML5 in QWebKit (+ gstreamer 1.0) - qt

Question

I am currently working on an i.MX6 SoC-based system... I've just built Qt 5.3.2 (through Yocto) configuring it for using gstreamer 1.0 as backend...
The compilation completes successfully, but unluckily I am not able to play HTML5 video from QWebKit...
Looking at the console output of my application (a simple QML-based application showing a WebView full-screen) I see the messages from gstreamer (so I think that the library is initialized and working)...
QML debugging is enabled. Only use this in a safe environment.
QEglFSImx6Hooks will set environment variable FB_MULTI_BUFFER=2 to enable double
buffering and vsync.
If this is not desired, you can override this via: export QT_EGLFS_IMX6_NO_FB_M
ULTI_BUFFER=1
[ 53.214914] PU: Power-off latency exceeded, new value 35000 ns
====== AIUR: 4.0.3 build on Feb 26 2016 12:18:25. ======
Core: MPEG4PARSER_06.09.10 build on Jan 8 2015 07:06:50
file: /usr/lib/imx-mm/parser/lib_mp4_parser_arm11_elinux.so.3.2
------------------------
Track 00 [video_0] Enabled
Duration: 0:09:56.458304000
Language: und
Mime:
video/x-h264, parsed=(boolean)true, alignment=(string)au, stream-format=
(string)avc, width=(int)853, height=(int)480, framerate=(fraction)24/1, codec_da
ta=(buffer)014d401effe10015274d401ea9181b07bcde00d4040406db0ad7bdf01001000428de0
9c8
------------------------
Track 01 [subtitle]: Disabled
Codec: 0, SubCodec: 0
------------------------
------------------------
Track 02 [audio_0] Enabled
Duration: 0:09:56.480000000
Language: und
Mime:
audio/mpeg, mpegversion=(int)4, channels=(int)6, rate=(int)48000, bitrat
e=(int)448000, stream-format=(string)raw, codec_data=(buffer)11b0
------------------------
====== BEEP: 4.0.3 build on Feb 26 2016 12:18:37. ======
Core: AAC decoder Wrapper build on Apr 22 2014 09:43:50
file: /usr/lib/imx-mm/audio-codec/wrap/lib_aacd_wrap_arm12_elinux.so.3
CODEC: BLN_MAD-MMCODECS_AACD_ARM_03.09.00_CORTEX-A8 build on Jun 19 2014 18:30:
32.
As you can see, gstreamer also reports the correct duration (length) of the video resource, but then I am not able to start the playback... The "play" button shown on screen is "greyed" and the duration of the media is reported as "00:00"... Even clicking on the "track bar" does not produce any results...
A screenshot of what is appearing on screen here follows:
Any ideas?