We used to only track the first one but this was wrong, so we start
tracking all the children properties here, adapting the test which
was already thought for this to be implemented.
At the same time add some flags to determine how children properties
need to be handled adding a mode that means that all duplicated
children props will be set together when the user sets that particular
child property. This is going to be tested in a following commit.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/918>
Making it possible to properly handle compositors that have those
properties as doubles and handle antialiasing.
Internally we were handling those values as doubles in framepositioner,
so expose new properties so user can set values as doubles also.
This changes the GESFramePositionMeta API but we are still on time for 1.24
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6241>
If we don't specify a path for loading, the runtime linker will search
for the library instead, which will use the usual mechanisms: RPATHs,
LD_LIBRARY_PATH, PATH (on Windows), etc.
Also try harder to load a non-devel libpython using INSTSONAME, if
available.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6159>
Timeline StreamCollection are very specific to inner working of nested
timelines and should not interfere with the usual stream selection
process and are now handled as element messages.
Stream selection inside `nleobject` need to be handled internally by the
application or GES itself so we should just drop all those as they would
interfere and fail if they are exposed to other elements.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5983>
Until now when doing `+test-clip blue +effect effect1 + effect effect2`
leaded to the following pseudo pipeline
videotestsrc ! effect2 ! effect1
given the `ges-launch` syntax this is quite unexpected and this needed
fixing
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5735>
This allows user to be in control of when scaling happens in the pipeline.
It can be plugged as an effect and scaling will be forced to happen in
the effect instead of in the compositor.
Without this, it would not be possible for users to, for example,
crop a video source before scaling to the target source size.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5735>
When requesting an asset from different threads we had no
guarantee that during the time we lookup an asset (which didn't exist)
and the time we create the asset with the same type/ID another thread
could not end up doing the same thing. In turns we could end up with
2 different threads loading the exact same asset and the cache
basically forgetting about one of the entries meaning that the user
would never get notified about one of those being ready to be used.
There was also the case when requesting "sync" where the user was
requesting an asset while another thread is creating it so it was
still in "ASSET_INITIALIZING" state, meaning that the returned asset
would be NULL which would be considered as an error in apps.
Since the cache lock is recursive we can just take it during the whole
ges_asset_request_async call and have other method still hold it.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5732>
When a new discoverer was created for a thread so discovery could
recurse we could end up removing the wrong discoverer info from the
cache leading to freeing it while it was still discovering URIS, which
lead to the following assertion:
``` bt
Thread 1 (Thread 0x7fcc2e1a5840 (LWP 1855496)):
#0 __pthread_kill_implementation (threadid=<optimized out>, signo=signo@entry=6, no_tid=no_tid@entry=0) at pthread_kill.c:44
#1 0x00007fcc2e9d98a3 in __pthread_kill_internal (signo=6, threadid=<optimized out>) at pthread_kill.c:78
#2 0x00007fcc2e9878ee in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
#3 0x00007fcc2e96f8ff in __GI_abort () at abort.c:79
#4 0x00007fcc2ed80056 in g_assertion_message (domain=domain@entry=0x7fcc2f2c19f9 "GES", file=file@entry=0x7fcc2f2dfd68 "../subprojects/gst-editing-services/ges/ges-discoverer-manager.c", line=line@entry=20, func=func@entry=0x7fcc2f2e0030 <__func__.7> "ges_discoverer_data_free", message=message@entry=0x12dab70 "assertion failed: (data->n_uri == 0)") at ../glib/gtestutils.c:3497
#5 0x00007fcc2ede1d87 in g_assertion_message_expr (domain=domain@entry=0x7fcc2f2c19f9 "GES", file=file@entry=0x7fcc2f2dfd68 "../subprojects/gst-editing-services/ges/ges-discoverer-manager.c", line=line@entry=20, func=func@entry=0x7fcc2f2e0030 <__func__.7> "ges_discoverer_data_free", expr=expr@entry=0x7fcc2f2dfcf1 "data->n_uri == 0") at ../glib/gtestutils.c:3523
#6 0x00007fcc2f2bd5c5 in ges_discoverer_data_free (data=0x160e430) at ../subprojects/gst-editing-services/ges/ges-discoverer-manager.c:20
#7 0x00007fcc2ed8509d in g_atomic_rc_box_release_full (clear_func=0x7fcc2f2bd4f0 <ges_discoverer_data_free>, mem_block=0x160e430) at ../glib/garcbox.c:355
#8 g_atomic_rc_box_release_full (mem_block=0x160e430, clear_func=0x7fcc2f2bd4f0 <ges_discoverer_data_free>) at ../glib/garcbox.c:338
#9 0x00007fcc2eda6809 in g_hash_table_remove_internal (notify=1, key=0x10448a0, hash_table=0x12e0be0) at ../glib/ghash.c:1776
#10 g_hash_table_remove (hash_table=0x12e0be0, key=0x10448a0) at ../glib/ghash.c:1804
#11 0x00007fcc2f2bd95f in cleanup_discoverer_cb (discoverer_data=discoverer_data@entry=0x13e7000) at ../subprojects/gst-editing-services/ges/ges-discoverer-manager.c:379
#12 0x00007fcc2edbc759 in g_timeout_dispatch (source=0x15a6060, callback=0x7fcc2f2bd910 <cleanup_discoverer_cb>, user_data=0x13e7000) at ../glib/gmain.c:5121
#13 0x00007fcc2edbbe1c in g_main_dispatch (context=0x1044700) at ../glib/gmain.c:3476
#14 g_main_context_dispatch_unlocked (context=0x1044700) at ../glib/gmain.c:4284
#15 0x00007fcc2ee16d78 in g_main_context_iterate_unlocked.isra.0 (context=0x1044700, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at ../glib/gmain.c:4349
#16 0x00007fcc2edbd407 in g_main_loop_run (loop=0x12ccbd0) at ../glib/gmain.c:4551
#17 0x00007fcc2f285791 in ges_uri_clip_asset_request_sync (uri=uri@entry=0x12d7980 "file:///var/home/phil/gstreamer/build/subprojects/gst-integration-testsuites/logs/ges/scenarios/check_seek_on_very_deeply_nested_timeline/nested_timeline_depth6.xges", error=error@entry=0x7fff499015a8) at ../subprojects/gst-editing-services/ges/ges-uri-asset.c:688
#18 0x00007fcc2f28949b in ges_project_create_asset_sync (project=0x12c1c70, id=id@entry=0x12d7980 "file:///var/home/phil/gstreamer/build/subprojects/gst-integration-testsuites/logs/ges/scenarios/check_seek_on_very_deeply_nested_timeline/nested_timeline_depth6.xges", extractable_type=extractable_type@entry=Python Exception <class 'gdb.error'>: value has been optimized out , error=error@entry=0x7fff499015a8) at ../subprojects/gst-editing-services/ges/ges-project.c:959
#19 0x00007fcc2f2ba484 in _ges_get_asset_from_timeline (timeline=timeline@entry=0x12bdc80, type=type@entry=Python Exception <class 'gdb.error'>: value has been optimized out , id=id@entry=0x12d7980 "file:///var/home/phil/gstreamer/build/subprojects/gst-integration-testsuites/logs/ges/scenarios/check_seek_on_very_deeply_nested_timeline/nested_timeline_depth6.xges", error=error@entry=0x7fff49901728) at ../subprojects/gst-editing-services/ges/ges-structured-interface.c:540
#20 0x00007fcc2f2ba9b2 in _ges_add_clip_from_struct (timeline=0x12bdc80, structure=0x157f690, error=0x7fff49901728) at ../subprojects/gst-editing-services/ges/ges-structured-interface.c:697
#21 0x00007fcc2f2b6a9d in _validate_action_execute (scenario=0x15f7620, action=0x157f500) at ../subprojects/gst-editing-services/ges/ges-validate.c:922
#22 0x00007fcc2eef5c9c in gst_validate_execute_action (action=0x157f500, action_type=0x13e0500) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:2541
#23 gst_validate_execute_action (action_type=0x13e0500, action=0x157f500) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:2507
#24 0x00007fcc2eef8ce3 in execute_next_action_full (scenario=<optimized out>, message=<optimized out>) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:2782
#25 0x00007fcc2eef9dee in _action_set_done (action=0x157efb0) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6368
#26 0x00007fcc2edbd26d in g_main_context_invoke_full (context=0x1044700, priority=200, function=0x7fcc2eef9ab0 <_action_set_done>, data=0x157efb0, notify=0x7fcc2eeea5d0 <gst_validate_action_unref>) at ../glib/gmain.c:6533
#27 0x00007fcc2eef6cf2 in gst_validate_action_set_done (action=0x157efb0) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6411
#28 0x00007fcc2eef9018 in execute_next_action_full (scenario=<optimized out>, message=<optimized out>) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:2803
#29 0x00007fcc2eef9dee in _action_set_done (action=0x157ea60) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6368
#30 0x00007fcc2edbd26d in g_main_context_invoke_full (context=0x1044700, priority=200, function=0x7fcc2eef9ab0 <_action_set_done>, data=0x157ea60, notify=0x7fcc2eeea5d0 <gst_validate_action_unref>) at ../glib/gmain.c:6533
#31 0x00007fcc2eef6cf2 in gst_validate_action_set_done (action=0x157ea60) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6411
#32 0x00007fcc2eef9018 in execute_next_action_full (scenario=<optimized out>, message=<optimized out>) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:2803
#33 0x00007fcc2eef9dee in _action_set_done (action=0x157e510) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6368
#34 0x00007fcc2edbd26d in g_main_context_invoke_full (context=0x1044700, priority=200, function=0x7fcc2eef9ab0 <_action_set_done>, data=0x157e510, notify=0x7fcc2eeea5d0 <gst_validate_action_unref>) at ../glib/gmain.c:6533
#35 0x00007fcc2eef6cf2 in gst_validate_action_set_done (action=0x157e510) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6411
#36 0x00007fcc2eef9018 in execute_next_action_full (scenario=<optimized out>, message=<optimized out>) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:2803
#37 0x00007fcc2eef9dee in _action_set_done (action=0x157df10) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6368
#38 0x00007fcc2edbd26d in g_main_context_invoke_full (context=0x1044700, priority=200, function=0x7fcc2eef9ab0 <_action_set_done>, data=0x157df10, notify=0x7fcc2eeea5d0 <gst_validate_action_unref>) at ../glib/gmain.c:6533
#39 0x00007fcc2eef6cf2 in gst_validate_action_set_done (action=0x157df10) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6411
#40 0x00007fcc2eef9018 in execute_next_action_full (scenario=<optimized out>, message=<optimized out>) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:2803
#41 0x00007fcc2eef9dee in _action_set_done (action=0x157d9e0) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6368
#42 0x00007fcc2edbd26d in g_main_context_invoke_full (context=0x1044700, priority=200, function=0x7fcc2eef9ab0 <_action_set_done>, data=0x157d9e0, notify=0x7fcc2eeea5d0 <gst_validate_action_unref>) at ../glib/gmain.c:6533
#43 0x00007fcc2eef6cf2 in gst_validate_action_set_done (action=0x157d9e0) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6411
#44 0x00007fcc2eef9018 in execute_next_action_full (scenario=<optimized out>, message=<optimized out>) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:2803
#45 0x00007fcc2eef9dee in _action_set_done (action=0x157d3e0) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6368
#46 0x00007fcc2edbd26d in g_main_context_invoke_full (context=0x1044700, priority=200, function=0x7fcc2eef9ab0 <_action_set_done>, data=0x157d3e0, notify=0x7fcc2eeea5d0 <gst_validate_action_unref>) at ../glib/gmain.c:6533
#47 0x00007fcc2eef6cf2 in gst_validate_action_set_done (action=0x157d3e0) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6411
#48 0x00007fcc2eef9018 in execute_next_action_full (scenario=<optimized out>, message=<optimized out>) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:2803
#49 0x00007fcc2eef9dee in _action_set_done (action=0x157cf70) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6368
#50 0x00007fcc2edbd26d in g_main_context_invoke_full (context=0x1044700, priority=200, function=0x7fcc2eef9ab0 <_action_set_done>, data=0x157cf70, notify=0x7fcc2eeea5d0 <gst_validate_action_unref>) at ../glib/gmain.c:6533
#51 0x00007fcc2eef6cf2 in gst_validate_action_set_done (action=0x157cf70) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6411
#52 0x00007fcc2eef9018 in execute_next_action_full (scenario=<optimized out>, message=<optimized out>) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:2803
#53 0x00007fcc2eef9dee in _action_set_done (action=0x157cb00) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6368
#54 0x00007fcc2edbd26d in g_main_context_invoke_full (context=0x1044700, priority=200, function=0x7fcc2eef9ab0 <_action_set_done>, data=0x157cb00, notify=0x7fcc2eeea5d0 <gst_validate_action_unref>) at ../glib/gmain.c:6533
#55 0x00007fcc2eef6cf2 in gst_validate_action_set_done (action=0x157cb00) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6411
#56 0x00007fcc2eef9018 in execute_next_action_full (scenario=<optimized out>, message=<optimized out>) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:2803
#57 0x00007fcc2eef9dee in _action_set_done (action=0x157c690) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6368
#58 0x00007fcc2edbd26d in g_main_context_invoke_full (context=0x1044700, priority=200, function=0x7fcc2eef9ab0 <_action_set_done>, data=0x157c690, notify=0x7fcc2eeea5d0 <gst_validate_action_unref>) at ../glib/gmain.c:6533
#59 0x00007fcc2eef6cf2 in gst_validate_action_set_done (action=0x157c690) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6411
#60 0x00007fcc2eef9018 in execute_next_action_full (scenario=<optimized out>, message=<optimized out>) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:2803
#61 0x00007fcc2eef9dee in _action_set_done (action=0x157c220) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6368
#62 0x00007fcc2edbd26d in g_main_context_invoke_full (context=0x1044700, priority=200, function=0x7fcc2eef9ab0 <_action_set_done>, data=0x157c220, notify=0x7fcc2eeea5d0 <gst_validate_action_unref>) at ../glib/gmain.c:6533
#63 0x00007fcc2eef6cf2 in gst_validate_action_set_done (action=0x157c220) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6411
#64 0x00007fcc2eef9018 in execute_next_action_full (scenario=<optimized out>, message=<optimized out>) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:2803
#65 0x00007fcc2eef9dee in _action_set_done (action=0x15233c0) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6368
#66 0x00007fcc2edbd26d in g_main_context_invoke_full (context=0x1044700, priority=200, function=0x7fcc2eef9ab0 <_action_set_done>, data=0x15233c0, notify=0x7fcc2eeea5d0 <gst_validate_action_unref>) at ../glib/gmain.c:6533
#67 0x00007fcc2eef6cf2 in gst_validate_action_set_done (action=0x15233c0) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6411
#68 0x00007fcc2eef9018 in execute_next_action_full (scenario=<optimized out>, message=<optimized out>) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:2803
#69 0x00007fcc2eef9dee in _action_set_done (action=0x1522f80) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6368
#70 0x00007fcc2edbd26d in g_main_context_invoke_full (context=0x1044700, priority=200, function=0x7fcc2eef9ab0 <_action_set_done>, data=0x1522f80, notify=0x7fcc2eeea5d0 <gst_validate_action_unref>) at ../glib/gmain.c:6533
#71 0x00007fcc2eef6cf2 in gst_validate_action_set_done (action=0x1522f80) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6411
#72 0x00007fcc2eef9018 in execute_next_action_full (scenario=<optimized out>, message=<optimized out>) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:2803
#73 0x00007fcc2eef9dee in _action_set_done (action=0x1522ae0) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6368
#74 0x00007fcc2edbd26d in g_main_context_invoke_full (context=0x1044700, priority=200, function=0x7fcc2eef9ab0 <_action_set_done>, data=0x1522ae0, notify=0x7fcc2eeea5d0 <gst_validate_action_unref>) at ../glib/gmain.c:6533
#75 0x00007fcc2eef6cf2 in gst_validate_action_set_done (action=0x1522ae0) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6411
#76 0x00007fcc2eef9018 in execute_next_action_full (scenario=<optimized out>, message=<optimized out>) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:2803
#77 0x00007fcc2eef9dee in _action_set_done (action=0x1522190) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6368
#78 0x00007fcc2edbd26d in g_main_context_invoke_full (context=0x1044700, priority=200, function=0x7fcc2eef9ab0 <_action_set_done>, data=0x1522190, notify=0x7fcc2eeea5d0 <gst_validate_action_unref>) at ../glib/gmain.c:6533
#79 0x00007fcc2eef6cf2 in gst_validate_action_set_done (action=0x1522190) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6411
#80 0x00007fcc2eef9018 in execute_next_action_full (scenario=<optimized out>, message=<optimized out>) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:2803
#81 0x00007fcc2eef9dee in _action_set_done (action=0x1520ea0) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6368
#82 0x00007fcc2edbd26d in g_main_context_invoke_full (context=0x1044700, priority=200, function=0x7fcc2eef9ab0 <_action_set_done>, data=0x1520ea0, notify=0x7fcc2eeea5d0 <gst_validate_action_unref>) at ../glib/gmain.c:6533
#83 0x00007fcc2eef6cf2 in gst_validate_action_set_done (action=0x1520ea0) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:6411
#84 0x00007fcc2eef9018 in execute_next_action_full (scenario=<optimized out>, message=<optimized out>) at ../subprojects/gst-devtools/validate/gst/validate/gst-validate-scenario.c:2803
#85 0x00007fcc2edbc759 in g_timeout_dispatch (source=0x14b6340, callback=0x7fcc2eef99c0 <execute_next_action>, user_data=0x15f7620) at ../glib/gmain.c:5121
#86 0x00007fcc2edbbe1c in g_main_dispatch (context=0x1044700) at ../glib/gmain.c:3476
#87 g_main_context_dispatch_unlocked (context=0x1044700) at ../glib/gmain.c:4284
#88 0x00007fcc2ee16d78 in g_main_context_iterate_unlocked.isra.0 (context=context@entry=0x1044700, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at ../glib/gmain.c:4349
#89 0x00007fcc2edb9a93 in g_main_context_iteration (context=context@entry=0x1044700, may_block=may_block@entry=1) at ../glib/gmain.c:4414
#90 0x00007fcc2ec14c3d in g_application_run (application=application@entry=0x1042ab0, argc=argc@entry=4, argv=argv@entry=0x7fff499031e8) at ../gio/gapplication.c:2577
#91 0x0000000000405dfd in real_main (argv=0x7fff499031e8, argc=4) at ../subprojects/gst-editing-services/tools/ges-launch.c:38
#92 main (argc=4, argv=0x7fff499031e8) at ../subprojects/gst-editing-services/tools/ges-launch.c:56
```
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5619>
The manager keeps track of one discoverer per thread and in large applications
with hundreds of threads this can significantly increase memory pressure. So we
need to periodically clean-up the unused discoverers.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5608>
When using deeply nested timelines with the `ges:` protocol the
formatters ends up trying to do discovery from the same thread current
discovery happens, leading to infinite freeze as GstDiscoverer can't run
several discoveries at the same time.
By ensuring that when calling `gst_discoverer_discover_uri_async` no
`GstDiscoverer` is set as "thread discoverer" we know that another
discoverer will be created if discovery recurses, effectively removing
the freeze.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5608>
Formatters might call "loaded" from the `gessrc` streaming thread
meaning that the `->formatters` field need to be protected.
Several other APIs are called from gesbasedemux, in some radom
thread, so we should ensure that this is all MT. safe, and the API
makes it simple.
Co-authored-by: Philippe Normand <philn@igalia.com>
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5431>
ges-timeline-element property getter handler was using
g_value_take_object() with internal pointers of the element as
arguments, instead of g_value_set_object().
g_value_take_object() moves the ownership of the reference; hence,
when reading "timeline" the reference ownership of timeline is moved
away from the ges-timeline-element and into the GValue.
Since GValues are temporaries that are often discarded quickly after,
this can easily lead to a double free. This was causing
gst-editing-services / pythontests to crash when running
TestTrackElements.test_ungroup_regroup() because of an innocent read of
`clip2.props.timeline` around the end of the test.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4924>
