Here’s a couple of posts that may help (or maybe not!).
There’s also a lot of talk that by calibrating your monitor to a custom setting, it affects the gamma when exporting a file to H.264.
Some folks have said that putting your monitor back to one of the default settings before exporting (then back to your custom setting afterwards) fixes the problem. I haven’t tried it.
Ed
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This one is from Chris Meyer and includes debunking of some solutions:
https://provideocoalition.com/index.php/cmg_blogs/story/brightness_issues_with_h264_quicktime_movies/P0/
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Open the QT
Go to “Window/Show Movie Properties”
Select “Video Track”, then click the “Visual Settings” tab
At the bottom left, change the transparency to “Blend” then move the slider to 100
Change the transparency to “Straight Alpha”
Close the Movie Properties window, then play or scrub the QT. Your black levels should now look correct
Save over old .mov
This is for PC’s. On the mac you change the transparency to “composition.”
And use “Save As…” from the File menu and select “Save as a self-contained movie.”
This adds the Fast Start information to the file.
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Update on x264encoder.
There is a way to make the exported file maintain a consistent appearance whether you are in a 2.2 or 1.8 gamma workspace. I’m thrilled I figured this out.
Choose x264encoder in the QTpro export pulldown.
Click Options
Click the Extra Options tab
Change the pulldown menu that says “No nclc atom” to one of the other options (I chose 6-1-6)
Make sure the “Add gamma 2.2 (legacy atom)” is NOT checked.
Hit OK and export your movie.
Now you have an h.264 encoded movie with correct gamma, and the appearance stays the same between 2.2 and 1.8 workspaces. (Confirm this by opening your display color preferences and toggling the gamma settings while your quicktime movie is open.)