1. If you really mst adjustbrightness/contrst... to each video file then you must buy a new display.
2. Those functions are available through the videocard drivers. Maybe you did upgraded them ?
3. Does this happens with all video files (to be unable to adjust) or with some types of video files (just MPEG or MKV ones)
4. Can you tell us wich filters/decoders are used to play the files ?
5. Have you tryied changing the video rendering methode from internal overlay to overlay mixer and back ?
6. Your OS ?
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