Section 7 of ST 2059, dubbed "Video Signal Generation", describes how to find the next `alignment point` at time `t` for a given broadcast video signal. Subsection 7.2, dubbed "Digital Standard Definition Television", has a table of entries with one of the rows containing the following data:

Table 2 – Signal Generation – Digital Standard Definition Television

Code: Select all

```
+--------------------------+---------+----------------+-----------------------------------+---------------------------+------------------------------+--------------------------------+-----------------+------------------------+
| Television System | Fr Rate | SMPTE Standard | Horizontal Alignment (Y Sample) P | Vertical Alignment Line L | Y samples per total line (H) | Y Samples per active line (HA) | Total Lines (V) | Sampling Clk Freq (SR) |
+--------------------------+---------+----------------+-----------------------------------+---------------------------+------------------------------+--------------------------------+-----------------+------------------------+
| 625 line Interl 13.5 MHz | 25 | SMPTE ST 125 | 736 | 1 | 864 | 720 | 625 | 13.5 x 10^6 |
+--------------------------+---------+----------------+-----------------------------------+---------------------------+------------------------------+--------------------------------+-----------------+------------------------+
```

- T = 1 / SR

- NextAlignmentPoint = int(t / (H x V x T) + 1) x (H x V x T)

where:

- `t` is elapsed continuous time from SMPTE Epoch in seconds. Note: This is the same as PTP time for PTP-based implementations.

- `T` is the period of the sampling clock in seconds.

- `H` is the duration of an entire video line in sample clock periods.

- `V` is the duration of a complete frame in lines.

- `R` is Sample Clock Frequency

The formula for `NextAlignmentPoint` is the one of interest.

So for 625-line interlaced (and using the table above), I believe that:

- T = 1 / 13.5 x 10^6
- V = 625
- H = (no clue - does it use 864 here?)