When to use ColorMatrix

[MysteryX]

I saw someone mentioning in another thread to use this line to fix colors
ColorMatrix(mode="Rec.601->Rec.709")

Now my question is: when should I use this line, and when should I not? Which types of videos require it?

[AzraelNewtype]

You use that when you are upscaling an SD video to HD and don't trust whatever players will be consuming the video to obey the colormatrix flagging from the metadata and just display as if it was 709 even if you flagged correctly.

[MysteryX]

You use that when you are upscaling an SD video to HD
How would you define SD in this case?
It should be used for upscaling 288p VCD to 720p?
It should be used for upscaling 576p DVD to 1080p?
What about for doubling a 720p YouTube video to 1440p?
What about upscaling a 360p YouTube video to 720p?

and don't trust whatever players will be consuming the video to obey the colormatrix flagging from the metadata and just display as if it was 709 even if you flagged correctly.
Which means? What should I do if I don't trust the player? Throw the computer out the window? :P

Are there cases where I should use any other color matrix conversion for encoding videos?

[TheSkiller]

There is no defined hard threshold but generally anything with more than 576 lines is usually considered HD and should be using the Rec.709 color coefficients.

So you should be using ColorMatrix(mode="Rec.601->Rec.709") whenever you are resizing SD content to something larger than 576 lines.


Are there cases where I should use any other color matrix conversion for encoding videos?Yes, likewise you should use ColorMatrix(mode="Rec.709->Rec.601") when you are resizing HD content to or below 576 lines.



It should be used for upscaling 288p VCD to 720p?Yes.
It should be used for upscaling 576p DVD to 1080p?Yes.
What about for doubling a 720p YouTube video to 1440p?No.
What about upscaling a 360p YouTube video to 720p?Yes. Albeit YouTube is special, you should always upload Rec.709 to YouTube (even a 480p video) because they do not care at all about the general convention and use Rec.709 for anything.

[MysteryX]

Oh, do you mean I shouldn't rely on file metadata to determine whether or not to fix colors? I checked with MediaInfo.dll and couldn't find any information about the color matrix.