rtmp2sink: add docs section with since marker on new stop-commands property

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1256>

rtmp2: fix code style, update documentation cache

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1256>

rtmp2: Clean up (improve) GstRtmpStopCommands type

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1256>

rtmp2sink: handle EOS event and close stream

https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/issues/1285

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1256>

mpegtsmux: Make handling of sinkpads thread-safe

Ensure we take the object lock while accessing `GstElement.sinkpads`.
Use an iterator when the code isn't simple to avoid deadlock.

When we find the best pad, take a reference so a concurrent pad
release doesn't destroy the pad before we're done with it.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1553>

hlssink2: Actually release splitmuxsink's pads

It was looking at the "outer" peer of the ghost pad, not the "inner"
peer (the target).

It provided the wrong pad to gst_element_release_request_pad.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1551>

mpegtsmux: Don't create streams with reserved PID

There are quite a few reserved PID in the various MPEG-TS (and derivate)
specifications which we should definitely not use. Those PID have a certain
meaning and purpose.

Furthermore, a lot of the code in the muxer implementation also makes assumption
on the purpose of streams based on their PID.

Therefore, when requesting a pad with a specific PID, make sure it is not a
restricted PID.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1561>

ci: include template from gst-ci master branch again

Back to development

Release 1.18.0

meson: dist pot file in tarball

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1558>

gst: Update for gst_video_transfer_function_*() function renaming

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1557>

tests: mpegtsmux: Test that we can manipulate pads after stop

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1552>

mpegtsmux: Keep mux usable after stop

Otherwise you cannot request new pads until after it is started again.

gst_base_ts_mux_reset with FALSE is still called in the dispose
implementation, so the muxer still gets deallocated when we actually
clean up.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1552>

msdkvp9dec: change the include header order

This fixes the compiler error when MFX_VERSION_USE_LATEST is defined in
the SDK.

/usr/include/mfx/mfxvp9.h:48:5: error: unknown type name ‘mfxExtBuffer’
     mfxExtBuffer Header;

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1549>

rtmp2: Need to unescape the userinfo before setting

This regressed in 827afa206d8c9675f2a7af402396552c2ed1df09. The same
fix was also committed to the webrtc element, but rtmp2 was missed.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1547>

webrtc: Clean up the userinfo unescaping code

Continuation from 04fd705906f4bd4cf1901001484e60c21e1b3139. This is
easier to understand and also avoids two copies.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1547>

dshowsrcwrapper: Update build instructions. Add _builddir to include search path.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1537>

modplug: avoid division by zero

Under some conditions, GetMaxPosition() returns zero, which should cause
position queries to fail rather than crash.

webrtc: Unescape turnserver user and password

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1530>

meson: allow the user to disable opencv

Allow the user to really disable opencv through meson (i.e.
-Dopencv=disabled).

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1533>

sctp: usrsctp: increase DIAG_MSG_LEN to accomodate longer file path

Fixes "‘%s’ directive output truncated writing XX bytes into
a region of size NN [-Wformat-truncation=]" compiler warnings.

https://github.com/sctplab/usrsctp/pull/521

Fixes #1389

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1540>

dshowsrcwrapper: fix typo in variable name

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1538>

vulkan: fix the enumtypes install path

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1528>

wpe: skip glbasesrc decide_allocation when non-GL caps are negotiated

Checking for GL caps features in gl_start() was done too late in case the parent
class fails to setup a working GL context. The element now determines if GL
support should be enabled during the decide-allocation query handling.

Additionally, when no GL context was found, we need to handle the element
cleanup because in that situation glbasesrc won't call gl_stop.

Fixes https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/issues/1376

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1532>

codecs: h264decoder: Fix possible GstH264Picture leak and small cleanup

Don't leak pictures when dpb is full unexpectedly.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1527>

d3d11videosink: Fix crash caused by missing null termination

gst_caps_features_new() must be null terminated.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1524>

va: allocator: remove parameter from _create_buffer_surface()

Don't the allocator to _create_buffer_surface() since it's not used.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1516>

va: utils: free allocated string

and fix a memleak

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1516>

va: utils: fix log category initialization

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1516>

va: h264dec: check va allocator at decide allocation

And some code cleanups

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1516>

va: decoder: improve locks for member variable access

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1516>

webrtc/datachannel: clear the error after use

Fixes a memory leak

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1535>

webrtc/datachannel: free previous protocol/label fields

Fixes a memory leak

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1535>

tests/webrtc: unref GBytes after use

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1535>

sctpdec: unref after retrieving the static pad template

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1535>

Release 1.17.90

webrtc/ice: resolve .local candidates internally

Requires the system's DNS resolver to support mdns resolution.

Fixes interoperablity with recent versions of chrome/firefox that
produce .local address in for local candidates.

Fixes https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/issues/1139

srtobject: set error when canceled waiting for a caller

To propagate error, this commit sets a reason. Otherwise, the function
caller should check if `error` is NULL when the return value is not normal.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1522>

srtobject: fix typo, s/errorj/error

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1522>

docs: fix gst-docs build if opencv is not being built

The disabler in opencv_dep (retrieved via libs_doc) will
cause a meson interpreter error if opencv is not being built:

ERROR: The += operator currently only works with arrays, dicts, strings or ints
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1519>

fdkaacenc: Implement flush function

The internal fdk encoder always produces 1024 bytes even with no input,
so special care should be taken to not drain it twice.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1515>

mediafoundation: Correct wrong raw video format mapping

Was a shameful mistake

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1517>

va: h264dec: set latency

The min latency is calculated with the maximum number of frames that
precede any frame, if available, and it is lower than the maximum
number of frames in DBP.

The max latency is calculated with the maxium size of frames in DBP.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1500>

fdkaacenc: Refactor layout selection code

No functional change.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1359>

fdkaacenc: Move channel layouts to gstfdkaac.c

In preparation of sharing them with the decoder. Iteration of the
channel layouts needs to be changed to use a sentinel element.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1359>

vulkan: docs annotation updates

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1506>

build/vulkan: split vulkan gir

also add to docs

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1506>

wpe: WebView and WebContext handling fixes

The WPEThreaded view is now split in 2 classes:
- WPEContextThread handles the persistent WebKit thread, where all WebKit API
calls should be handled.
- WPEView: is created from the WPEContextThread. It handles the WebView and
maintains the public interface on which wpesrc relies. This is the facade for
the WebView, basically. It takes care of dispatching API calls into the context
thread.

With these fixes it is now possible to create (and reuse) mutlple wpesrc
elements during the application lifetime.

Fixes #1372

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1484>

sctp: fix build with GST_DISABLE_GST_DEBUG

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1465>

sctp: hook up internal copy of libusrsctp to build

Add option 'sctp-internal-usrsctp' so people can choose
to build againts the distro version instead.

Fixes https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/issues/870

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1465>

sctp: import internal copy of usrsctp library

There are problems with global shared state and no API stability
guarantees, and we can't rely on distros shipping the fixes we
need. Both firefox and Chrome bundle their own copies too.

Imported from https://github.com/sctplab/usrsctp,
commit 547d3b46c64876c0336b9eef297fda58dbe1adaf
Date: Thu Jul 23 21:49:32 2020 +0200

Fixes https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/issues/870

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1465>

proxysink: event_function needs to handle the event when it is disconnecetd from proxysrc

without this a disconneted proxysink fail when goes to play with error:

 Internal data stream error.
 streaming stopped, reason error (-5)

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1508>

cccombiner: Correct sink_query chain up and fix caps leaks

Don't chain up to src_query() from sink_query() method, and
returned caps by gst_static_pad_template_get_caps() needs to be
cleared.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1513>

mediafoundation: Call MFShutdown when destroying plugin

MFStartup and MFShutdown should be paired as documented in
https://docs.microsoft.com/en-us/windows/win32/api/mfapi/nf-mfapi-mfstartup#remarks
Otherwise valgrind-like tools would report false positive memory leak.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1512>

msdkvpp: do not hold too many input buffers in locked list

If the surface is locked before vpp, upstream takes the reference.
We do not need to take a reference for msdk in vpp.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1490>

msdkvpp: refact, put input and output surface in diffrent list

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1490>

Correct typos in gsth264parse.c

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1511>

d3d11: Handle newly added GST_VIDEO_TRANSFER_BT601

Use the value for mapping between DXGI_COLOR_SPACE_TYPE and GstVideoColorimetry.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1410>

d3d11: Store more device information in context structure

It would be more informative for debugging

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1507>

d3d11: Selected adapter index should be unsigned integer

If d3d11device was created successfully, the index of adapter
must not be negative value

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1507>

h264parse: Add new H.264 levels

The spec now list 6, 6.1 and 6.2.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1509>

va: h264dec: remove spurious comment

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1499>

va: h264dec: check return value of gst_va_handle_set_context()

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1499>

smoothstreaming: start closer to the edge in live streams

It is more appropriate to start closer to the live edge in
live streams. Some live streams maintain a large dvr window
(over few hours in some cases), so starting from the first
fragment will be too far away from the live edge.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1346>

cccombiner: Update for additional info parameter to the "samples-selected" signal

See https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/590

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1498>

build: update for gl pkg-config file split

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1462>

docs: include *.cc and *.hh in gst-c-sources

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1491>

mpeg2enc: add disable-encode-retries property

MJPEG Tools may reencode pictures in a second pass to stick
closer to the target bitrate. This can result in slower than
real-time encoding for full HD content in certain situations,
as entire GOPs need reencoding when the reference picture is
reencoded.

See https://sourceforge.net/p/mjpeg/bugs/141/ for background

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1491>

mpeg2enc: report a latency

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1491>

mpeg2enc: finalize GstVideoEncoder port

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1491>

mpeg2enc: store video encoder instance directly in stream writer class

Instead of storing the pad and then only using it to get the
element.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1491>

mpeg2enc: remove unused streamwriter member 'buf'

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1491>

mpeg2enc: remove some unused code

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1491>

mpeg2enc: remove code paths for older mjpegtools versions

Gets rid of lots of code paths that no one has built,
used or tested for ages, and makes code more maintainable.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1491>

mpeg2enc: initial port to GstVideoEncoder base class

https://bugzilla.gnome.org/show_bug.cgi?id=685414

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1491>

decklink: Re-order modes enum for backwards compatibility with 1.16

The PAL/NTSC widescreen modes were added after 1.16 but inserted before
the HD modes, which changed the integer values of the enums.

Move them to the very end instead to keep backwards compatibility.

Fixes https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/issues/1048

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1492>

srt: Add support for using hostnames instead of IP addresses

If an address can't be parsed as IP address, try resolving it via
GResolver instead. SRT URIs more often than not contain hostnames and
without trying to resolve them we won't be able to handle such URIs.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1493>

cccombiner: update to new samples selection API

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1497>

opencv: compile with -Wno-format-nonliteral

opencv plugin is pulling a header which makses clang++ 10
complain a lot and blocks -werror.

```
/usr/include/opencv4/opencv2/flann/logger.h:83:36: error: format string is not a string literal [-Werror,-Wformat-nonliteral]
        int ret = vfprintf(stream, fmt, arglist);
                                   ^~~
```

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1494>

player: Add g_autoptr() support

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1495>

gstlv2utils.c: avoid implicit float to int conversion

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1487>

gstautoconvert.c: fix clang warnings

clang 10 is complaining about incompatible types due to the
glib typesystem.

```
gst-plugins-bad/gst/autoconvert/b5c3019@@gstautoconvert@sha/gstautoconvert.c.o' -c ../subprojects/gst-plugins-bad/gst/autoconvert/gstautoconvert.c
../subprojects/gst-plugins-bad/gst/autoconvert/gstautoconvert.c:898:8: error: incompatible pointer types passing 'typeof ((((void *)0))) *' (aka 'void **') to parameter of type 'GList **' (aka 'struct _GList **') [-Werror,-Wincompatible-pointer-types]
  if (!g_atomic_pointer_compare_and_exchange (&autoconvert->factories, NULL,
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/glib-2.0/glib/gatomic.h:192:44: note: expanded from macro 'g_atomic_pointer_compare_and_exchange'
    __atomic_compare_exchange_n ((atomic), &gapcae_oldval, (newval), FALSE, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST) ? TRUE : FALSE; \
                                           ^~~~~~~~~~~~~~
1 error generated.
```

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1487>

gstladspautils.c: avoid implicit float to int conversion

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1487>

androidmedia: ignore additional camera effects if not present

Fixes https://gitlab.freedesktop.org/gstreamer/cerbero/-/issues/283

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1470>

meson: Only look for Obj-C/C++ compilers on macOS/iOS

On Windows, MinGW-GCC Objective-C/C++ compilers can be in PATH and
mess up the build since they may not match the CPU family of the C/C++
compilers we are using.

Also require them on macOS/iOS, because they should always be present.

Fixes https://gitlab.freedesktop.org/gstreamer/gst-build/-/issues/88

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1488>

va: h264dec: log if upstream pool is kept

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1489>

va: utils: fix precondition check for handle_context_query()

display paramater can be NULL, but if it's not, it has to be a
GstVaDisplay.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1489>

va: tests: example: Fix memory leaks

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1489>

srtobject: Add support for IPv6

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1477>

srtobject: Reset parameters before setting URI

This makes `gst_srt_object_validate_parameters` work properly since
`localaddress` and `localport` will be missing if the URL did not
provide them.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1477>

srtobject: Simplify gst_srt_object_set_*_value

This fixes `gst_srt_object_set_string_value` in particular because the
value might not be a static string.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1477>

srtobject: Store passphrase like other parameters

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1477>

webrtc, rtmp2: Warn if the user or password aren't escaped

If the user/pass aren't escaped, the userinfo will be ambiguous and we
won't know where to split. We will accidentally get it right if the :
belongs in the password.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1481>

webrtc, rtmp2: Fix parsing of userinfo in URI strings

While parsing the string, `gst_uri_from_string()` also unescapes the
userinfo. This is bad if your username contains a `:` character, since
we will then split the userinfo at the wrong location when parsing it.

To fix this, we can use the new `gst_uri_from_string_escaped()` API
that was added in
https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/583

Fixes https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/issues/831

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1481>

tests: examples: add va-x11-render example

This a GTK+ example will share, through GstContext, a custom X11
VADisplay to a pipeline using vah264dec and appsink.

When the frames are processed for rendering, the VASurfaceID is
fetched from the buffer and it is rendered using vaPutSurface in a X11
widget.

tests: examples: Comply with compilation order

va: allocator: support for GST_MAP_VA map flag

This flag will return the VASurface value at mapping

va: context: instanciate VA display through GstContext

Add all the machinery to instanciate VA display through GstContext,
thus all va elements can share the same display and the user can set
a custom one.

va: h264dec: don't copy frames if VAMemory capsfeature is negotiated

Otherwise the VASurfaceID is lost.