UI: Fix falling back to non-multitrack output after error

This lambda would be called from the Qt event loop rather than the
original call stack when continuing from an error, resulting in the
captured references being invalid.
To solve this must explicitly use a copy instead of reference capture.

UI/window-basic-main-outputs.cpp

@@ -1060,7 +1060,7 @@ std::shared_future<void> SimpleOutput::SetupStreaming(obs_service_t *service, Se
 	auto audio_bitrate = GetAudioBitrate();
 	auto vod_track_mixer = IsVodTrackEnabled(service) ? std::optional{1} : std::nullopt;
 
-	auto handle_multitrack_video_result = [&](std::optional<bool> multitrackVideoResult) {
+	auto handle_multitrack_video_result = [=](std::optional<bool> multitrackVideoResult) {
 		if (multitrackVideoResult.has_value())
 			return multitrackVideoResult.value();
 
@@ -1100,7 +1100,7 @@ std::shared_future<void> SimpleOutput::SetupStreaming(obs_service_t *service, Se
 	};
 
 	return SetupMultitrackVideo(service, GetSimpleAACEncoderForBitrate(audio_bitrate), 0, vod_track_mixer,
-				    [&, continuation](std::optional<bool> res) {
+				    [=](std::optional<bool> res) {
 					    continuation(handle_multitrack_video_result(res));
 				    });
 }
@@ -2021,7 +2021,6 @@ std::shared_future<void> AdvancedOutput::SetupStreaming(obs_service_t *service,
 							SetupStreamingContinuation_t continuation)
 {
 	int multiTrackAudioMixes = config_get_int(main->Config(), "AdvOut", "StreamMultiTrackAudioMixes");
-	int idx = 0;
 
 	bool is_multitrack_output = allowsMultiTrack();
 
@@ -2049,7 +2048,7 @@ std::shared_future<void> AdvancedOutput::SetupStreaming(obs_service_t *service,
 	const char *audio_encoder_id = config_get_string(main->Config(), "AdvOut", "AudioEncoder");
 	int streamTrackIndex = config_get_int(main->Config(), "AdvOut", "TrackIndex") - 1;
 
-	auto handle_multitrack_video_result = [&](std::optional<bool> multitrackVideoResult) {
+	auto handle_multitrack_video_result = [=](std::optional<bool> multitrackVideoResult) {
 		if (multitrackVideoResult.has_value())
 			return multitrackVideoResult.value();
 
@@ -2088,6 +2087,7 @@ std::shared_future<void> AdvancedOutput::SetupStreaming(obs_service_t *service,
 		if (!is_multitrack_output) {
 			obs_output_set_audio_encoder(streamOutput, streamAudioEnc, 0);
 		} else {
+			int idx = 0;
 			for (int i = 0; i < MAX_AUDIO_MIXES; i++) {
 				if ((multiTrackAudioMixes & (1 << i)) != 0) {
 					obs_output_set_audio_encoder(streamOutput, streamTrack[i], idx);
@@ -2100,7 +2100,7 @@ std::shared_future<void> AdvancedOutput::SetupStreaming(obs_service_t *service,
 	};
 
 	return SetupMultitrackVideo(service, audio_encoder_id, static_cast<size_t>(streamTrackIndex),
-				    VodTrackMixerIdx(service), [&, continuation](std::optional<bool> res) {
+				    VodTrackMixerIdx(service), [=](std::optional<bool> res) {
 					    continuation(handle_multitrack_video_result(res));
 				    });
 }