EAV (the end of active video signal) and SAV (the start of active video signal ) are two timing reference codes synchronize HD, VD, and FIELD to the video data. At the start and end of each video data block, the device sends a unique timing reference code. SAV is the start code and EAV is the end code. Between EAV and SAV, there is the horizontal blanking interval which does not contain any information related to the video signal, i.e. the digital signal does not contain the sync pulse. ITU-R BT.656 SAV and EAV codes proceed and follow valid data, as shown in the following figure.
According to the book "Digital Video and Audio Broadcasting Technology", the SAV and EAV code words consist of four 8 or 10 bit code words each. SAV and EAV begins with one code word in which all bits are set to one, followed by two words in which all bits are set to zero. The fourth code word contains information about the respective field or the vertical blanking interval, respectively. This fourth code word is used for detecting the start of a frame, field and active picture area in the vertical direction. The most significant bit of the fourth code word is always 1. The next bit (bit 8 in a 10 bit transmission or bit 6 in an 8 bit transmission) flags the field; if this bit is set to zero, it is a line of the first field and if it is set to one, it is a line of the second field. The next bit (bit 7 in a 10 bit transmission or bit 5 in an 8 bit transmission) flags the active video area in the vertical direction. If this bit is set to zero, then this is the visible active video area and if not, it is the vertical blanking interval. Bit 6 (10 bit) or bit 4 (8 bit) provides information about whether the present code word is an SAV or an EAV. It is SAV if this bit is set to zero and EAV if it is not. Bits 5...2 (10 bit) or 3...0 (8 bit) are used for error protection of the SAV and EAV code words. Code word 4 of the timing reference sequence (TRS) contains the following information:
- F = Field (0 = 1st field, 1 = 2nd field)
- V = Vertical blanking (1 = vertical blanking interval active)
- H = SAV/EAV identification (0 = SAV, 1 = EAV)
- P0, P1, P2, P3 = Protection bits (Hamming code)
2. EAV/SAV in 1080p Video
SAV specifies the start of active video on a horizontal line in sample units. EAV specifies the end of active video on a horizontal line in sample units. For 1080p video SMPTE274M standard, EAV and SAV are shown in the following figure.
Lines 42 – 1122 make up the 1080 horizontal lines of active video. The vertical lines of active video are defined by the total horizontal resolution (A) minus the horizontal blanking count (B) as shown in the following table.