1.Open your video file with Gom player. 

2. Right-click on the main interface and select Preferences to open the Preferences settings dialog box. You also can press F5 on the keyboard to enable the dialog for short. 

3.Click on the Subtitle button on the left. Choose the Subtitles tab on the right panel. In the Subtitle Font section, uncheck the Auto Size option, then you can adjust the font and size of the subtitle. In the Subtitle Color & Opacity section, click the three color boxes to select subtitle color. In the Subtitle Position & Spacing section, you also can change the position of the subtitle.

4.Click on the close button on the bottom left corner to exit the dialog box and enjoy your video playback.

The skilled users can play in Video option in Preferences with the video settings: change the output type according to your hardware configuration. At overlay color key the user can define his/her own colors or use those already defined.

Video effect settings permit setting deblock and video effects like smoothening, sharpening and adding noise to the video. We're still in the Video tab of the Preference menu, and at Screen Size, believe it or not (I've seen it before and it kind of became a standard in the latest video players), you can change Gom Player's screen size (a new option is changing only if it doesn't correspond to a user-defined resolution).