What are embedded syncs and external syncs for video?

zhao yanjie said:

Could you help me to explain what's embedded syncs,what's external syncs,and the difference between embedded syncs and external syncs.

Embedded syncs means that the synchronization signals are embedded into the data stream of the bus, in other words there are special values that come across the data bus which represent the start of active video (SAV) and end of active video (EAV). The physical lines of a digital video signal which use embedded syncs consist only of the data bus and a clock, for an 8 bit video system this means you only need 9 pins. An example standard implementation of this is BT.656 for SDTV or BT.1120 for HDTV.

External syncs means that there are separate physical lines that toggle to indicate the start of lines and frames, which are the horizontal sync and vertical sync lines. The physical lines of a digital video signal which use external syncs consist of the data bus, clock, and additional lines for the synchronization signals (hsync, vsync, field id, possibly others), for an 8 bit video stream this means you will need at least 11 pins. 

There are many books out there on the topic of digital video which discuss this sort of thing, I found Video Demystified, a Handbook for the Digital Engineer to be helpful, I have the older third edition, but there seem to be newer versions.

Maybe the ITU specifications can give you a well help, BT1120 BT1364 BT656 BT601 have very detail interpretation about this topic.