How to get the remaining cast time of a CHANNELED spell?

[fpsware]

I'm trying to get the remaining cast time in milliseconds of a channeled spell. I can do this for a CAST spell but not a CHANNELED spell.

Eg... if Mind Flay has a total channeled time for 2000ms, and its been channeling for 1500ms I want to see there is only 500ms remaining.

 

[Jianyu]

Quartz Add-on?

EDIT: Quartz - Modular Casting Bar : Casting Bars, Cooldowns : World of Warcraft AddOns