Correct is use the same color format for color transfer-primaries-space ?

[Aug]

Hello.
Thanks for reading my topic.
I see enconders have options to select an color format for color primaries , color transfer and color space.
I see for 720P and 1080P the color format is bt709.
Thus for better quality the correct is choice the same color format bt709 for color primaries, color transfer and color space ?
Selecting the same color format optimize the enconding compression ? Selecting alternate colors format for the same video file can break the quality ?

Have an nice week.

[_Al_]

Technically it has nothing to do with quality. Only if you use wrong flag for a video, it is shown in slightly wrong colors.

Those are just flags in your video, telling a player what equations to use to get RGB values. Your video is encoded using YUV values, so to view any YUV video, it needs to be converted to RGB for a preview on RGB screen.

So if you know those flags, you set them the same, as your original video was in encoding settings.

Other thing is to change them. For example, you have matrix BT601, your original video, your video was 720x480, and you are upscaling to HD resolution, so you better use BT709 flags for upscaled video, to prevent confusion during playback. To do that, you have to change those values, not just flags, so you have to encode to your new values to your new matrix, primaries, transfer. You cannot just simply change your flags only.

so:
- so if you know your original flags, encode them the same
- if you are changing them, you convert, to those matrixes, if conversion effect is not available, you might get hands on some LUT, that does the same, or apps like avisynth or vapoursynth do that (not easy to use, where you specify input and convert to output).
Or for example ffmpeg, I just google it, do not use ffmpeg for these conversion:

ffmpeg -i input.mp4 -vf "colorspace=all=bt709:iall=bt601-6-625" output.mp4

-vf "colorspace=...": Applies the colorspace video filter.
all=bt709: Sets the output color space, primaries, and transfer function to BT.709.
iall=bt601-6-625: Specifies that the input color space, primaries, and transfer function should be treated as BT.601-6-625 (for PAL). For NTSC, you would use iall=bt601-6-525.