1-2-1 Unspecified Gamma 2.4 Color space Tag

[bastientrehoux]

Hello,
It would be a great option to add the possibility in the Subler app to change the color space tag of the MP4/MOV file to the 1-2-1 tag (it corresponds to Rec709 with Unspecified gamma curve) to help avoid QuickTime Color Management issues with some apps which change some 1-2-1 tags to 1-1-1. It is currently impossible with the last version of Subler (1.9.1).

This YouTube video explains the problem and why it could be interesting in some cases to tag QuickTime or MP4 files as 1-2-1 for color space instead of 1-1-1:
https://www.youtube.com/watch?v=1QlnhlO6Gu8

Thanks for reading this message and taking it into consideration to improve the Subler app.

[galad87]

"Unspecified" means unspecified, aka every app will do something different, it doesn't mean gamma 2.4.

If Davinci and VLC can't properly display Rec.709, that's their problem, I won't add a crappy workaround to Subler.

[bastientrehoux]

I’m sorry if I haven’t been clear in my explanations. I didn’t you to offense you. The problem appears to be more complex than what my previous message could let you think, unfortunately.

The YouTube video linked in my previous message has been made by a professional color scientist which has obviously done a great job of research to write his video. To summarise, he explains that QuickTime does not consider the 1-1-1 tag as gamma 2.4 but other software, which are not properly programmed such as VLC or Firefox, does apply gamma 2.4 to tag 1-1-1. According to him, the official way to impose QuickTime to read a file as gamma 2.4 is to tag the file at 1-2-1 with some other little fine details I admit I can’t understand at all.
DaVinci Resolve, for instance, when you explicitly ask the app to export as Rec709 and gamma 2.4 tag the file as 1-2-1 whereas some other apps like HandBrake, when you import a 1-2-1 and then export a re-encoded file retag as 1-1-1 and causes the QuickTime gamma shift issue after when the file is opened in QuickTime.

I agree with you that your app is not intended to fix other apps bugs. I just wanted to let you that, because your app is an advanced metadata editor, some users might be interested by such features. You can now do whatever you want with those pieces of information.

My message was just a suggestion. Subler is your app and you have the right to do whatever you want with it.

Thanks for reading me.

[galad87]

Not to brag, but I've been around for years, and I know the whole saga. QuickTime on macOS uses an approximation that's almost similar to the result of an actual implementation of bt.1886. The issue is that many softwares ignore the monitor color profile, and do only half of the color management work (and this when we are lucky).

HandBrake guesses a value when the input is unspecified, because unspecified color tag are unspecified by definition and will display differently in every player out there.

[galad87]

I guess Resolve writes the "gama" atom in MOV, but as far as I know it's not defined for MOV. And it's still an hacky thing.