frontend: Add replay buffer saving frontend event

docs/sphinx/reference-frontend-api.rst

@@ -150,6 +150,10 @@ Structures/Enumerations
 
      Triggered when the replay buffer has fully stopped.
 
+   - **OBS_FRONTEND_EVENT_REPLAY_BUFFER_SAVING**
+
+     Triggered when the replay buffer is saving.
+
    - **OBS_FRONTEND_EVENT_REPLAY_BUFFER_SAVED**
 
      Triggered when the replay buffer has been saved.

frontend/api/obs-frontend-api.h

@@ -65,6 +65,8 @@ enum obs_frontend_event {
 
 	OBS_FRONTEND_EVENT_CANVAS_ADDED,
 	OBS_FRONTEND_EVENT_CANVAS_REMOVED,
+
+	OBS_FRONTEND_EVENT_REPLAY_BUFFER_SAVING,
 };
 
 /* ------------------------------------------------------------------------- */

frontend/widgets/OBSBasic_ReplayBuffer.cpp

@@ -160,6 +160,8 @@ void OBSBasic::ReplayBufferSave()
 		return;
 	}
 
+	OnEvent(OBS_FRONTEND_EVENT_REPLAY_BUFFER_SAVING);
+
 	calldata_t cd = {0};
 	proc_handler_t *ph = obs_output_get_proc_handler(outputHandler->replayBuffer);
 	proc_handler_call(ph, "save", &cd);