One of the best sources for male Frankish garb is the Stuttgart Psalter. It is said to be made between 820 and 830 AD. An online copy is here:
http://digital.wlb-stuttgart.de/digitale-sammlungen/seitenansicht/?no_cache=1&tx_dlf%5Bid%5D=1517&tx_dlf%5Bpage%5D=1&Seite&cHash=813f9adc4abfd45131969ce66b5c8629 Note that many of the drawings may depict clothing concepts known or practiced circa 725 to 825 and have a Byzantine influence. Some men are dressed as representative of their station including royalty at court, Christ and saintly persons and the clergy.
Generally Frankish men wore a belted tunic that came to the knee and pants of various lengths. Woolen leg wraps were present under shoes or boots. A cloak and a hat were often worn. Note the variety of placement of decorative trim on the tunics. A superhumeral collar, shoulder roundels, wide close cuffs, central neckline trim extending to the waist and hem facings or trim sometimes defining a side slit are all seen in the psalter. Also there is often a trim band on the cloak, the cloak is closed with a large pin or brooch and a few pants have trim attached along the center front of both legs.
Check the red pants depicted above.