We used to conside elements that were subclassses of another
element type as being the same (for example with videoconvertscale,
bother videoconvert and videoscale are subclasses of videoconvertscale
and that code was lost)
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/899>
Removes the usage of [NSApp terminate] to avoid killing the process and thus never actually returning a value.
The new way is just to use [NSApp stop] and send an event, since stop only happens after an event is processed.
Unlike terminate, stop will only halt the event loop, not the whole process.
This uses an NSApplicationDelegate to listen for NSApp finishing the launch process, and then signals the 'main' thread
to proceed. That makes sure to never call [NSApp stop] before NSApp is actually running, which could happen if the
provided 'main' function finished quickly enough.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6005>
decodebin(3) runs a scheduling query before pads are activated which
ultimately triggers basesrc->start which will automatically call
`gst_base_src_start_complete` for any source that is not marked as
'async'. This calls will harmlessly bail out in `not_activated_yet`
so we should not warn in that case.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6011>
The output of VP9 and AV1 encoder is a little different from the H264
and H265 encoder, it may contain repeat frames and so the output frame
number may be more than the input. We need to call finish_subframe()
when some frame will be repeated later. So we need to extend the
current prepare_output() virtual function.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3015>
Converting from RGB to YUV: When comparing the info.colorimetry to
GST_VIDEO_COLORIMETRY_BT709 it does not make sense to look at the input
signal because that is of type of RGB. The plugin needs to look at the
output YUV-type and compare GST_VIDEO_COLORIMETRY_BT709 to that, because
that is the YUV-type the plugin needs to convert input-RGB into.
Converting from YUV to RGB: Comparing to the input is correct, but because
here the color encoding info BT601/BT709 is on input side of the plugin.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5998>
In the following backtrace for the deadlock, we can see that:
- In T8 `uridecodebin3` is exposing a new pad, in `pad_added_cb`,
`playbin3` is trying to get `GST_PLAY_BIN3_LOCK` in the callback. This
threads holds its `SELECTION_LOCK` in F17 `reconfigure_output_stream`,
which is looks right `decodebin3` is handling its selection state
in that code path
- In T7 `playbin3` holds the `GST_PLAY_BIN3_LOCK` when calling
`gst_element_post_message` in `gst_play_bin3_send_event` which is
not necessary in that section of the code.
``` bt
Thread 8 (Thread 0x7f0b78ee36c0 (LWP 2952467) "multiqueue0:src"):
#0 futex_wait (private=0, expected=2, futex_word=0x1fa6d60) at ../sysdeps/nptl/futex-internal.h:146
#1 __GI___lll_lock_wait (futex=futex@entry=0x1fa6d60, private=0) at lowlevellock.c:49
#2 0x00007f0b858cd46a in lll_mutex_lock_optimized (mutex=0x1fa6d60) at pthread_mutex_lock.c:48
#3 ___pthread_mutex_lock (mutex=0x1fa6d60) at pthread_mutex_lock.c:128
#4 0x00007f0b7e665720 in pad_added_cb (uridecodebin=0x1fb4050, pad=0x7f0b54022060, playbin=0x1fb00e0) at ../subprojects/gst-plugins-base/gst/playback/gstplaybin3.c:2463
#5 0x00007f0b85c00060 in g_closure_invoke (closure=0x1fa9eb0, return_value=0x0, n_param_values=2, param_values=0x7f0b78ee1dd0, invocation_hint=0x7f0b78ee1d50) at ../gobject/gclosure.c:832
#6 0x00007f0b85c2cf66 in signal_emit_unlocked_R.isra.0 (node=node@entry=0x1c5bf30, detail=detail@entry=0, instance=instance@entry=0x1fb4050, emission_return=emission_return@entry=0x0, instance_and_params=instance_and_params@entry=0x7f0b78ee1dd0) at ../gobject/gsignal.c:3796
#7 0x00007f0b85c1d4da in g_signal_emit_valist (instance=<optimized out>, signal_id=<optimized out>, detail=<optimized out>, var_args=var_args@entry=0x7f0b78ee1f90) at ../gobject/gsignal.c:3549
#8 0x00007f0b85c1d6f3 in g_signal_emit (instance=<optimized out>, signal_id=<optimized out>, detail=<optimized out>) at ../gobject/gsignal.c:3606
#9 0x00007f0b85e20c3e in gst_element_add_pad (element=0x1fb4050, pad=0x7f0b54022060) at ../subprojects/gstreamer/gst/gstelement.c:802
#10 0x00007f0b7e632620 in add_output_pad (dec=0x1fb4050, target_pad=0x7f0b6400fda0) at ../subprojects/gst-plugins-base/gst/playback/gsturidecodebin3.c:717
#11 0x00007f0b7e632788 in db_pad_added_cb (element=0x1fb8020, pad=0x7f0b6400fda0, dec=0x1fb4050) at ../subprojects/gst-plugins-base/gst/playback/gsturidecodebin3.c:736
#12 0x00007f0b85c00060 in g_closure_invoke (closure=0x1fb7fc0, return_value=0x0, n_param_values=2, param_values=0x7f0b78ee2300, invocation_hint=0x7f0b78ee2280) at ../gobject/gclosure.c:832
#13 0x00007f0b85c2cf66 in signal_emit_unlocked_R.isra.0 (node=node@entry=0x1c5bf30, detail=detail@entry=0, instance=instance@entry=0x1fb8020, emission_return=emission_return@entry=0x0, instance_and_params=instance_and_params@entry=0x7f0b78ee2300) at ../gobject/gsignal.c:3796
#14 0x00007f0b85c1d4da in g_signal_emit_valist (instance=<optimized out>, signal_id=<optimized out>, detail=<optimized out>, var_args=var_args@entry=0x7f0b78ee24c0) at ../gobject/gsignal.c:3549
#15 0x00007f0b85c1d6f3 in g_signal_emit (instance=<optimized out>, signal_id=<optimized out>, detail=<optimized out>) at ../gobject/gsignal.c:3606
#16 0x00007f0b85e20c3e in gst_element_add_pad (element=0x1fb8020, pad=0x7f0b6400fda0) at ../subprojects/gstreamer/gst/gstelement.c:802
#17 0x00007f0b7e6260b4 in reconfigure_output_stream (output=0x7f0b5400def0, slot=0x7f0b64013dd0, msg=0x7f0b78ee26b8) at ../subprojects/gst-plugins-base/gst/playback/gstdecodebin3.c:3086
#18 0x00007f0b7e623700 in check_slot_reconfiguration (dbin=0x1fb8020, slot=0x7f0b64013dd0) at ../subprojects/gst-plugins-base/gst/playback/gstdecodebin3.c:2455
#19 0x00007f0b7e623e62 in multiqueue_src_probe (pad=0x7f0b6001e600, info=0x7f0b78ee2930, slot=0x7f0b64013dd0) at ../subprojects/gst-plugins-base/gst/playback/gstdecodebin3.c:2544
#20 0x00007f0b85e53aaa in probe_hook_marshal (hook=0x7f0b74040500, data=0x7f0b78ee28c0) at ../subprojects/gstreamer/gst/gstpad.c:3669
#21 0x00007f0b85c88a3e in g_hook_list_marshal (hook_list=0x7f0b6001e698, may_recurse=1, marshaller=0x7f0b85e53786 <probe_hook_marshal>, data=0x7f0b78ee28c0) at ../glib/ghook.c:674
#22 0x00007f0b85e541be in do_probe_callbacks (pad=0x7f0b6001e600, info=0x7f0b78ee2930, defaultval=GST_FLOW_OK) at ../subprojects/gstreamer/gst/gstpad.c:3853
#23 0x00007f0b85e5ac9c in gst_pad_push_event_unchecked (pad=0x7f0b6001e600, event=0x7f0b64002120, type=GST_PAD_PROBE_TYPE_EVENT_DOWNSTREAM) at ../subprojects/gstreamer/gst/gstpad.c:5538
#24 0x00007f0b85e54bc2 in push_sticky (pad=0x7f0b6001e600, ev=0x7f0b78ee2a60, user_data=0x7f0b78ee2ac0) at ../subprojects/gstreamer/gst/gstpad.c:4057
#25 0x00007f0b85e4a13c in events_foreach (pad=0x7f0b6001e600, func=0x7f0b85e54a8e <push_sticky>, user_data=0x7f0b78ee2ac0) at ../subprojects/gstreamer/gst/gstpad.c:613
#26 0x00007f0b85e54f91 in check_sticky (pad=0x7f0b6001e600, event=0x7f0b64002120) at ../subprojects/gstreamer/gst/gstpad.c:4116
#27 0x00007f0b85e5b65e in gst_pad_push_event (pad=0x7f0b6001e600, event=0x7f0b64002120) at ../subprojects/gstreamer/gst/gstpad.c:5706
#28 0x00007f0b7e5888e7 in gst_single_queue_push_one (mq=0x1fbb000, sq=0x7f0b64013b70, object=0x7f0b64002120, allow_drop=0x7f0b78ee2c3c) at ../subprojects/gstreamer/plugins/elements/gstmultiqueue.c:2068
#29 0x00007f0b7e58a1bc in gst_multi_queue_loop (pad=0x7f0b6001e600) at ../subprojects/gstreamer/plugins/elements/gstmultiqueue.c:2347
#30 0x00007f0b85e96a36 in gst_task_func (task=0x7f0b64016050) at ../subprojects/gstreamer/gst/gsttask.c:399
#31 0x00007f0b85e97e41 in default_func (tdata=0x7f0b640138d0, pool=0x1fbe9c0) at ../subprojects/gstreamer/gst/gsttaskpool.c:70
#32 0x00007f0b85cd1ab2 in g_thread_pool_thread_proxy (data=<optimized out>) at ../glib/gthreadpool.c:352
#33 0x00007f0b85ccc982 in g_thread_proxy (data=0x7f0b6006f640) at ../glib/gthread.c:831
#34 0x00007f0b858ca12d in start_thread (arg=<optimized out>) at pthread_create.c:442
#35 0x00007f0b8594bbc0 in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81
Thread 7 (Thread 0x7f0b7a7646c0 (LWP 2952434) "multiqueue3:src"):
#0 syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
#1 0x00007f0b85cf470c in g_mutex_lock_slowpath (mutex=0x1fb81d0) at ../glib/gthread-posix.c:1494
#2 0x00007f0b7e6281a2 in gst_decodebin3_send_event (element=0x1fb8020, event=0x7f0b6800a650) at ../subprojects/gst-plugins-base/gst/playback/gstdecodebin3.c:3561
#3 0x00007f0b85e23ca3 in gst_element_send_event (element=0x1fb8020, event=0x7f0b6800a650) at ../subprojects/gstreamer/gst/gstelement.c:1994
#4 0x00007f0b7e63806b in gst_uri_decodebin3_send_event (element=0x1fb4050, event=0x7f0b6800a650) at ../subprojects/gst-plugins-base/gst/playback/gsturidecodebin3.c:2227
#5 0x00007f0b85e23ca3 in gst_element_send_event (element=0x1fb4050, event=0x7f0b6800a650) at ../subprojects/gstreamer/gst/gstelement.c:1994
#6 0x00007f0b7e66375a in gst_play_bin3_send_event (element=0x1fb00e0, event=0x7f0b6800a650) at ../subprojects/gst-plugins-base/gst/playback/gstplaybin3.c:1863
#7 0x00007f0b85e23ca3 in gst_element_send_event (element=0x1fb00e0, event=0x7f0b6800a650) at ../subprojects/gstreamer/gst/gstelement.c:1994
#8 0x00007f0b85f61b5b in stream_selection_cb (bus=0x1dc2d80, message=0x7f0b68008b00, d=0x1d7de30) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:2235
#9 0x00007f0b85c00060 in g_closure_invoke (closure=0x1d2a5b0, return_value=0x0, n_param_values=2, param_values=0x7f0b7a7627b0, invocation_hint=0x7f0b7a762730) at ../gobject/gclosure.c:832
#10 0x00007f0b85c2cf66 in signal_emit_unlocked_R.isra.0 (node=node@entry=0x1c5e5f0, detail=detail@entry=235, instance=instance@entry=0x1dc2d80, emission_return=emission_return@entry=0x0, instance_and_params=instance_and_params@entry=0x7f0b7a7627b0) at ../gobject/gsignal.c:3796
#11 0x00007f0b85c1d4da in g_signal_emit_valist (instance=<optimized out>, signal_id=<optimized out>, detail=<optimized out>, var_args=var_args@entry=0x7f0b7a762970) at ../gobject/gsignal.c:3549
#12 0x00007f0b85c1d6f3 in g_signal_emit (instance=<optimized out>, signal_id=<optimized out>, detail=<optimized out>) at ../gobject/gsignal.c:3606
#13 0x00007f0b85e05be9 in gst_bus_sync_signal_handler (bus=0x1dc2d80, message=0x7f0b68008b00, data=0x0) at ../subprojects/gstreamer/gst/gstbus.c:1307
#14 0x00007f0b85e03834 in gst_bus_post (bus=0x1dc2d80, message=0x7f0b68008b00) at ../subprojects/gstreamer/gst/gstbus.c:364
#15 0x00007f0b85e2436c in gst_element_post_message_default (element=0x1fb00e0, message=0x7f0b68008b00) at ../subprojects/gstreamer/gst/gstelement.c:2127
#16 0x00007f0b85df42b1 in gst_bin_post_message (element=0x1fb00e0, msg=0x7f0b68008b00) at ../subprojects/gstreamer/gst/gstbin.c:2789
#17 0x00007f0b85e24627 in gst_element_post_message (element=0x1fb00e0, message=0x7f0b68008b00) at ../subprojects/gstreamer/gst/gstelement.c:2170
#18 0x00007f0b85df7c12 in gst_bin_handle_message_func (bin=0x1fb00e0, message=0x7f0b68008b00) at ../subprojects/gstreamer/gst/gstbin.c:4041
#19 0x00007f0b85e61bd3 in gst_pipeline_handle_message (bin=0x1fb00e0, message=0x7f0b68008b00) at ../subprojects/gstreamer/gst/gstpipeline.c:669
#20 0x00007f0b7e663fa4 in gst_play_bin3_handle_message (bin=0x1fb00e0, msg=0x7f0b68008b00) at ../subprojects/gst-plugins-base/gst/playback/gstplaybin3.c:2030
#21 0x00007f0b85df5a98 in bin_bus_handler (bus=0x1dc2cc0, message=0x7f0b68008b00, bin=0x1fb00e0) at ../subprojects/gstreamer/gst/gstbin.c:3263
#22 0x00007f0b85e037f1 in gst_bus_post (bus=0x1dc2cc0, message=0x7f0b68008b00) at ../subprojects/gstreamer/gst/gstbus.c:357
#23 0x00007f0b85e2436c in gst_element_post_message_default (element=0x1fb4050, message=0x7f0b68008b00) at ../subprojects/gstreamer/gst/gstelement.c:2127
#24 0x00007f0b85df42b1 in gst_bin_post_message (element=0x1fb4050, msg=0x7f0b68008b00) at ../subprojects/gstreamer/gst/gstbin.c:2789
#25 0x00007f0b85e24627 in gst_element_post_message (element=0x1fb4050, message=0x7f0b68008b00) at ../subprojects/gstreamer/gst/gstelement.c:2170
#26 0x00007f0b85df7c12 in gst_bin_handle_message_func (bin=0x1fb4050, message=0x7f0b68008b00) at ../subprojects/gstreamer/gst/gstbin.c:4041
#27 0x00007f0b7e638005 in gst_uri_decode_bin3_handle_message (bin=0x1fb4050, msg=0x7f0b68008b00) at ../subprojects/gst-plugins-base/gst/playback/gsturidecodebin3.c:2218
#28 0x00007f0b85df5a98 in bin_bus_handler (bus=0x1dc2e40, message=0x7f0b68008b00, bin=0x1fb4050) at ../subprojects/gstreamer/gst/gstbin.c:3263
#29 0x00007f0b85e037f1 in gst_bus_post (bus=0x1dc2e40, message=0x7f0b68008b00) at ../subprojects/gstreamer/gst/gstbus.c:357
#30 0x00007f0b85e2436c in gst_element_post_message_default (element=0x1fb8020, message=0x7f0b68008b00) at ../subprojects/gstreamer/gst/gstelement.c:2127
#31 0x00007f0b85df42b1 in gst_bin_post_message (element=0x1fb8020, msg=0x7f0b68008b00) at ../subprojects/gstreamer/gst/gstbin.c:2789
#32 0x00007f0b85e24627 in gst_element_post_message (element=0x1fb8020, message=0x7f0b68008b00) at ../subprojects/gstreamer/gst/gstelement.c:2170
#33 0x00007f0b7e61ee43 in sink_event_function (sinkpad=0x7f0b6400f8c0, dbin=0x1fb8020, event=0x7f0b6c097870) at ../subprojects/gst-plugins-base/gst/playback/gstdecodebin3.c:1450
#34 0x00007f0b85f51122 in gst_validate_pad_monitor_downstream_event_check (pad_monitor=0x7f0b6c094a80, parent=0x1fb8020, event=0x7f0b6c097870, handler=0x7f0b7e61e797 <sink_event_function>) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-pad-monitor.c:2101
#35 0x00007f0b85f535bf in gst_validate_pad_monitor_sink_event_full_func (pad=0x7f0b6400f8c0, parent=0x1fb8020, event=0x7f0b6c097870) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-pad-monitor.c:2406
#36 0x00007f0b85f537fa in gst_validate_pad_monitor_sink_event_func (pad=0x7f0b6400f8c0, parent=0x1fb8020, event=0x7f0b6c097870) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-pad-monitor.c:2418
#37 0x00007f0b85e5c523 in gst_pad_send_event_unchecked (pad=0x7f0b6400f8c0, event=0x7f0b6c097870, type=GST_PAD_PROBE_TYPE_EVENT_DOWNSTREAM) at ../subprojects/gstreamer/gst/gstpad.c:5940
#38 0x00007f0b85e5ae65 in gst_pad_push_event_unchecked (pad=0x7f0b6400f650, event=0x7f0b6c097870, type=GST_PAD_PROBE_TYPE_EVENT_DOWNSTREAM) at ../subprojects/gstreamer/gst/gstpad.c:5573
#39 0x00007f0b85e54bc2 in push_sticky (pad=0x7f0b6400f650, ev=0x7f0b7a763620, user_data=0x7f0b7a763680) at ../subprojects/gstreamer/gst/gstpad.c:4057
#40 0x00007f0b85e4a13c in events_foreach (pad=0x7f0b6400f650, func=0x7f0b85e54a8e <push_sticky>, user_data=0x7f0b7a763680) at ../subprojects/gstreamer/gst/gstpad.c:613
#41 0x00007f0b85e54f91 in check_sticky (pad=0x7f0b6400f650, event=0x7f0b6c097870) at ../subprojects/gstreamer/gst/gstpad.c:4116
#42 0x00007f0b85e5b65e in gst_pad_push_event (pad=0x7f0b6400f650, event=0x7f0b6c097870) at ../subprojects/gstreamer/gst/gstpad.c:5706
#43 0x00007f0b85e523e7 in event_forward_func (pad=0x7f0b6400f650, data=0x7f0b7a763820) at ../subprojects/gstreamer/gst/gstpad.c:3130
#44 0x00007f0b85e521e3 in gst_pad_forward (pad=0x7f0b6004f180, forward=0x7f0b85e522bd <event_forward_func>, user_data=0x7f0b7a763820) at ../subprojects/gstreamer/gst/gstpad.c:3084
#45 0x00007f0b85e525ab in gst_pad_event_default (pad=0x7f0b6004f180, parent=0x7f0b6400f650, event=0x7f0b6c097870) at ../subprojects/gstreamer/gst/gstpad.c:3181
#46 0x00007f0b85e5c523 in gst_pad_send_event_unchecked (pad=0x7f0b6004f180, event=0x7f0b6c097870, type=GST_PAD_PROBE_TYPE_EVENT_DOWNSTREAM) at ../subprojects/gstreamer/gst/gstpad.c:5940
#47 0x00007f0b85e5ae65 in gst_pad_push_event_unchecked (pad=0x7f0b64008360, event=0x7f0b6c097870, type=GST_PAD_PROBE_TYPE_EVENT_DOWNSTREAM) at ../subprojects/gstreamer/gst/gstpad.c:5573
#48 0x00007f0b85e54bc2 in push_sticky (pad=0x7f0b64008360, ev=0x7f0b7a763a60, user_data=0x7f0b7a763ac0) at ../subprojects/gstreamer/gst/gstpad.c:4057
#49 0x00007f0b85e4a13c in events_foreach (pad=0x7f0b64008360, func=0x7f0b85e54a8e <push_sticky>, user_data=0x7f0b7a763ac0) at ../subprojects/gstreamer/gst/gstpad.c:613
#50 0x00007f0b85e54f91 in check_sticky (pad=0x7f0b64008360, event=0x7f0b6c097870) at ../subprojects/gstreamer/gst/gstpad.c:4116
#51 0x00007f0b85e5b65e in gst_pad_push_event (pad=0x7f0b64008360, event=0x7f0b6c097870) at ../subprojects/gstreamer/gst/gstpad.c:5706
#52 0x00007f0b7e5888e7 in gst_single_queue_push_one (mq=0x7f0b60076540, sq=0x7f0b6c093300, object=0x7f0b6c097870, allow_drop=0x7f0b7a763c3c) at ../subprojects/gstreamer/plugins/elements/gstmultiqueue.c:2068
#53 0x00007f0b7e58a1bc in gst_multi_queue_loop (pad=0x7f0b64008360) at ../subprojects/gstreamer/plugins/elements/gstmultiqueue.c:2347
#54 0x00007f0b85e96a36 in gst_task_func (task=0x7f0b6c072050) at ../subprojects/gstreamer/gst/gsttask.c:399
#55 0x00007f0b85e97e41 in default_func (tdata=0x7f0b6c093ef0, pool=0x1fbe9c0) at ../subprojects/gstreamer/gst/gsttaskpool.c:70
#56 0x00007f0b85cd1ab2 in g_thread_pool_thread_proxy (data=<optimized out>) at ../glib/gthreadpool.c:352
#57 0x00007f0b85ccc982 in g_thread_proxy (data=0x7f0b70033800) at ../glib/gthread.c:831
#58 0x00007f0b858ca12d in start_thread (arg=<optimized out>) at pthread_create.c:442
#59 0x00007f0b8594bbc0 in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81
```
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5982>
A client may map dmabufs without the intention to either read or write
to the memory. One example is clients wanting to use the
`gst_video_frame_map()` helper function.
Thus, in order to make buffers from `GstVaDmabufAllocator` conveniently
usable, ignore the modifier check if the client specified neither
`GST_MAP_READ` nor `GST_MAP_WRITE`.
Also skip the `va_sync_surface()` call in that case, as it's likely only
needed for CPU reads/writes.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5965>
clang does not like the array index assignment without the `=` sign in
it. This is a gnu extension I believe, and adding the sign is proper.
This fixes the following two warnings:
```
../subprojects/gst-plugins-bad/gst-libs/gst/vulkan/gstvkvideo-private.c:32:40:
warning: use of GNU 'missing =' extension in designator [-Wgnu-designator]
[GST_VK_VIDEO_EXTENSION_DECODE_H264] {
^
=
../subprojects/gst-plugins-bad/gst-libs/gst/vulkan/gstvkvideo-private.c:36:40:
warning: use of GNU 'missing =' extension in designator [-Wgnu-designator]
[GST_VK_VIDEO_EXTENSION_DECODE_H265] {
^
=
```
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5996>
The internal elements are only created when caps on both video and subtitle pads
are known.
Prior to that, a GST_QUERY_CAPS on a video sink pad would just return ANY
instead of giving a hint of what downstream can actually handle and
prefers. This could result in upstream elements (such as decoders) deciding on
chosing (in the best cases) a non-optimal caps or (in the worst case) caps that
couldn't be handled by the elements downstream of subtitleoverlay.
In order to fix that, we assume that all subtitle "elements" handle the subtitle
overlay composition feature/meta and handle `GST_QUERY_CAPS` ourselves if the
internal elements aren't present yet.
Fixes#3176
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5834>
