mac-multitrack: disable encoder gpu scale

* disable gpu_scale_type for mac so that scene items are not skipped
* revert preferred colorspace to VIDEO_CS_709

Author: sandboxcoder

obs-studio-server/source/osn-multitrack-video-output.cpp

@@ -63,10 +63,20 @@ static void adjust_video_encoder_scaling(const obs_video_info &ovi, obs_encoder_
 	}
 
 	obs_encoder_set_scaled_size(video_encoder, requested_width, requested_height);
-	obs_encoder_set_gpu_scale_type(video_encoder, encoder_config.gpu_scale_type.value_or(OBS_SCALE_BICUBIC));
+#ifdef __APPLE__
+    // On Mac, only set GPU scale type to OBS_SCALE_DISABLE. Defaulting to BICUBIC, etc would
+    // trigger maybe_set_up_gpu_rescale to create an encoder_only_mix with a new owi pointer
+    // that doesn't match item->canvas, causing scene items to be skipped and black frames.
+    // Instead, leave gpu_scale_type at OBS_SCALE_DISABLE so the encoder connects directly to
+    // the canvas video mix and software (swscale) handles resolution downscaling.
+    obs_encoder_set_gpu_scale_type(video_encoder, OBS_SCALE_DISABLE);
+#else
+    obs_encoder_set_gpu_scale_type(video_encoder, encoder_config.gpu_scale_type.value_or(OBS_SCALE_BICUBIC));
+#endif
 	obs_encoder_set_preferred_video_format(video_encoder, encoder_config.format.value_or(VIDEO_FORMAT_NV12));
-	obs_encoder_set_preferred_color_space(video_encoder, encoder_config.colorspace.value_or(VIDEO_CS_DEFAULT));
+	obs_encoder_set_preferred_color_space(video_encoder, encoder_config.colorspace.value_or(VIDEO_CS_709));
 	obs_encoder_set_preferred_range(video_encoder, encoder_config.range.value_or(VIDEO_RANGE_PARTIAL));
+
 }
 
 static uint32_t closest_divisor(const obs_video_info &ovi, const media_frames_per_second &target_fps)
@@ -209,8 +219,6 @@ static bool create_video_encoders(const Config &go_live_config, std::shared_ptr<
 
 		if (obs_get_multiple_rendering()) {
 			obs_encoder_set_video_mix(encoder, obs_video_mix_get(ovi, OBS_STREAMING_VIDEO_RENDERING));
-		} else {
-			obs_encoder_set_video_mix(encoder, obs_video_mix_get(ovi, OBS_MAIN_VIDEO_RENDERING));
 		}
 
 		if (!obs_encoder_set_group(encoder, encoder_group.get())) {