How to change video color matrix flag

[MysteryX]

I've been upscaling and re-encoding several videos until I learned that I also needed to convert the color matrix from 601 to 709.

For the videos already encoded before changing this, is there a way to change the flag of these videos so that they are read as 601 instead of 709 so that their colors appear correctly without needing to re-encode them again?

This question isn't specifically about AviSynth, it would require a special editing tool of some kind to do so.

Thanks

[sneaker_ger]

For H.264 you can try this tool (http://forum.doom9.org/showthread.php?t=152419) but it's not developed anymore and not alway reliable.

[Asmodian]

Since, as far as I know, only madVR respects the color matrix flag you could also use file name tags. "matrix=601" in the file name will override the flag. If that tool doesn't work for you. :)

To be compatible with other renderers that use the naive >=720p is 709 rule you would have to re-encode.