Roll-up is a style where the text rolls onto the screen from the bottom or top one line at a time, rolling up to make room for a new line. Normally, a maximum of 3 lines are shown on the screen before the first line is taken off of the screen. This is the least time-consuming post-production process but still allows for good viewing. Roll-up captions are always used in live captioning and are typically used for one speaker programs such as teaching or preaching.
The text actually pops on the screen in blocks of 1 to 3 lines and is placed on the screen to not cover up any on-screen text or vital video. The time codes from your master are used to place these captions perfectly in sync with each frame. Pop-up captions are the preferred viewing style of the hearing impaired and are typically used for programs with multiples speakers or characters that are on the screen at any given time.