Add QT_GSTREAMER_CAMERABIN_VIDEOSRC environment variable.

It can be used to set which video source element should be used by
the camerabin.

Change-Id: I8d1cd8c4ba6fe5a89817699f645b0997e713aaca
Reviewed-by: Samuli Piippo <samuli.piippo@digia.com>
Reviewed-by: Christian Stromme <christian.stromme@digia.com>
WMF plugin: Initialize member variable m_stateDirty.

Fix purify warning:
[W] UMR: Uninitialized memory read in MFPlayerControl::refreshState(void) {1 occurrence}

Task-number: QTBUG-41966
Change-Id: I1416f906dcc8c31a528ab7f09a258873fcfe9d1e
Reviewed-by: Yoann Lopes <yoann.lopes@theqtcompany.com>
Doc: Added the missing screenshot image

Change-Id: Ifcef698bd735b7fe7e5f4a92984be07a01f283fb
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>
OpenSL ES: Don't store or return the adjusted volume level.

According to our own docs we should always return 1.0 (MAX) volume level
if the device doesn't support setting the volume, which is the case
for OpenSL ES on Android.

Task-number: QTBUG-42159
Change-Id: I9144e9e2cd84cc80633c68c5d6fa32b8dbd0fcd5
Reviewed-by: Yoann Lopes <yoann.lopes@theqtcompany.com>
OpenSL ES: improve buffer logic

Don't use relaxed load and stores, we need to be stricter to avoid
problems with high frequency re-fills of the buffer. If we don't enforce
ordering we might end-up spending more time trying to acquire an open
slot in the buffer. Updating processes bytes is also moved off the
"OpenSL" thread.

Added some comments for improved readability.

Change-Id: Ie27965fc6bf4b8394081ae6419f4933522ada98e
Reviewed-by: Yoann Lopes <yoann.lopes@theqtcompany.com>
Check whether current context can be obtained when deleting textures.

Add a warning in that case.

Task-number: QTBUG-41966
Change-Id: I491ee9e13c9504040ab789951656983a736d9203
Reviewed-by: Yoann Lopes <yoann.lopes@theqtcompany.com>
Merge remote-tracking branch 'origin/5.4' into dev

Change-Id: Id87e56ccfc9f33f98c3d06991f6fe9c14d38fbac