Some codec (H.264) are auto-adjusting
I might be imagining this, but I feel that the so-called auto-adjustment in QT for Windows became worse with QT7.
With PowerPoints, I would argue that the most efficient strategy is simply not to worry about gamma or fine grading.
Typically PPs are projected in environments where the ambient color temperature is all over the place. Even if you can turn the lights out, say, in a lecture hall, it's not an answer. Any experienced lecturer can tell you how that's the best way to send the audience to sleep.