Are horizontal and vertical back porches required for digital video, and if so, why?
I don't know if there are any TFT panels with LVDS interfaces that can work with zero porches, but usually they require at least some amount of non-active video pixels between active lines to know which pixel is first in line and long enough non-active period to understand which line is the first line. They do not use horizontal and vertical sync signals, but only data enable signal. With HDMI and SDI signaling, the timings exactly match timings of analog CRT systems as they were developed from analog interfaces. They both use the non-active pixel time to transmit audio channels and other metadata, and if there was not enough time between video lines this would not be possible. Also, by having selectable inactive time between lines, they can achieve compatibility with many different frame rates with identical pixel clock, rather than using separate pixel clock for say 24Hz and 30Hz vertical rates. On the other hand, interfaces such as DisplayPort have fixed link rate and it transmits video data in small packets, but the video data itself can have less inactive time when using VESA reduced blanking than with CEA standard video formats.