In the playback bar, click on. the icon that looks like the equaliser for lesser media players. This is right next to the playback button. Then select the 'video effects' tab.

The 'basic' tab will be selected by default. Check the 'image adjust' checkbox. From here, you can adjust the hue, saturation, contrast, brightness and gamma of the image. There is also a 'brightness threshold' slider. The Image adjust window The changed take place in real time, an this can be used to enhance dark videos.