As described in User Guide pages 4-11 and 12, as shown in Table 4-1 for each format, at a specific line (at the beginning of the HANC period) in each TRS word of EAV and SAV, Fig.4- tx_trs must be asserted for one pixel clock at the position shown in 16.
(In addition, depending on the format, 2 lines are required for 1 screen.)
If instructed, VPID insertion is done if there is no existing VPID on the Parallel Data In image stream. ("Rule 1" on page 4-12)
If there is an existing VPID or other ancillary data, the behavior depends on the configuration of the ancillary data and the value of the tx_vpid_overwrite signal as described in Rules 2 and 3, and the existing VPID is prioritized (retained) or overwritten, or the VPID is added. will be either
(Therefore, it is also possible to insert it on the user circuit side.)
The information to be inserted as VPID is not automatically calculated and must be given by 4 or 8 byte signals of tx_vipd_byte[4:1], tx_vpid_byte[4:1]_b.

https://www.altera.com/en_US/pdfs/literature/ug/ug_sdi_ii.pdf