A bug which was technically introduced in df446c3f6e: the author
assigned video mixes to the virtual camera and did not realize you have
to wait for full capture stop with the "deactivate" signal rather than
the "stop" signal. This situation is understandable because these
signals are likely confusing and need more documentation.
The way an output works when it stops is it has three stages:
- "stopping", which is the moment the user themselves stop the output
- "stop", when the output's implementation has stopped and returns
success or an error code
- "deactivate", when the output inself (not the implementation) has
fully stopped capturing encoded or raw frame data after the
implementation has stopped. This is done in a separate thread,
end_data_capture_thread(), for performance and data race reasons, and
is when it's "actually fully stopped for real this time"
(Lain note: I sincerely apologize for this confusing signal design)
The author of df446c3f6e was likely confused as to why they could not
destroy the video mix in the "stop" signal without triggering a race
condition in end_data_capture_thread(), and instead decided to make a
workaround to clear the video mix set to the output before destroying
the video mix. Unsetting the video mix I'm guessing *seemed* to fix the
problem for them at the time, and destroying the video mix separately
after that automatically stops capture, so it *technically* worked
because the deactivate thread cannot be called until the
implementation's stop signal has executed. However, it was still the
incorrect way to handle the problem, because it circumvents the output's
mechanism for deactivating the frame data capture by destroying the view
instead.
The reason this was the incorrect way to handle the problem became
exposed in 7cd7ca80f8, when tytan made it so it uses the main video mix
under certain circumstances. The main view is special and cannot be
destroyed, so the mechanism to stop frame data capture that the
virtualcam was using before failed, and raw frame data capture continued
perpetually until the end of the program erroneously.
This fix solves the bug by using the "deactivate" signal rather than the
"stop" signal, thus allowing the output to fully end its data capture
and *then* destroy the video mix.
Fixesobsproject/obs-studio#9153
Adds a check to make sure that delayed preload is ignored if the stinger
is restarted/interrupted. Just adds this check to the previous commit to
make sure that it doesn't redundantly try to preload a frame when
playback is restarted.
The `mp_media::obsframe` varaible is a variable used to store the
current frame, or the first frame on stop. However, it's never cleared,
and while decoding a frame, it's invalid. The variable was added for
delayed preloading of the first frame for stingers.
Now, for more context, when media sources stop, it stores the first
frame of the video so it can set the source's current async texture to
that frame, effectively preloading the first frame into the backend,
making it so that when you play back that media, it's able to start
playback instantly without having to wait for the thread to play back
that frame, causing seamless playback.
Normally, preload happens right when first frame is finished decoding,
thus it wasn't a problem before these variables and delayed preloading
was added. However, with stingers, I delayed that preload further
because stingers are kind of a special case because the stinger does not
clear itself right away on stop. Because of that, it was causing it to
flash the first frame at the end of the stinger. This is why `obsframe`
and `request_preload` were added: it's a way of signaling the media
source to preload the first frame when the stinger itself is fully
completed. It was added to fix that stinger bug.
However, if the user interrupts playback of the stinger (e.g. swaps to
another scene while in the middle of the transition), that
`request_preload` might still be queued and happen while the media
source is still decoding, and thus, while `obsframe` is invalid.
I realize that we should probably refactor and clean up the
media-playback lib.
Lain
