How can I send saved library videos through Snapchat?
Snapchat now has the desired capability of sending videos from the camera roll in 10 second chunks.

Head to Memories by clicking the circle (now “cards” in 2018) on the bottom center of the screen (or swiping up) on the camera screen and then go to camera roll section on top and long press the video you want and press the blue arrow to share it.