Eyevinn / go-608 / 30904827036

85%

main: 85%

Build Type

Pull #73

github

Committed by tobbee

Commit Message

fix(generate): drop the date from the default UTC caption line

608 drains one byte pair per frame, so a caption line's width is not a display preference but a direct claim on the per-second budget: a second holds round(fps)-1 usable pairs, since the last pair must land a frame before the next cue for the finished caption to be displayed at all. That is 24 pairs at 25 fps and 23 at 23.976.

The full RFC3339 timestamp cost 5 of them. Measured for the default two lines, centered, white over yellow, before and after:

  row 14                 pop-on  paint-on  roll-up  roll-up + unit reset
  2026-07-20T15:04:05Z     23       23        24            25
  15:04:05Z                18       18        19            20

Five go608-clock mode/policy combinations therefore did not fit their slice: roll-up under the default per-unit window reset at both 25 and 23.976 fps, and at 23.976 fps even plain pop-on. All eighteen combinations across 23.976/25/30 fps now build, with 3 pairs spare at the tightest rate. A side effect: the '~18 pairs, 0.6 s at 30 fps' figure that README, schedule/doc.go and generate/unitcue.go have all been quoting was describing a caption the code did not emit, and is now true.

Time-of-day is also the honest unit for what this caption is: the second is what you read against media time, and the date is fixed by -start for the length of any run worth watching. Z is kept, so the line stays unambiguously UTC. Only the default Config changed -- a caller wanting the full timestamp passes their own CueContentFunc.

Recorded as W9 in docs/design/cea608-wallclock-generation.md, which also notes why row 14 stays white: row 15 is already yellow, so a white row 14 is the default's only centered *white* line, and W6's one-column centering compensation applies only to coloured lines. Colouring both would leave every default run exercising just the compensated path.

Verified with ffmpeg's ccaption_dec over a spliced AVC input, not an internal round-trip:... (continued)

Pull Request Pull Request #73: fix(generate): drop the date from the default UTC caption line

Coverage Stats

9 of 13 new or added lines in 2 files covered. (69.23%)

48 existing lines in 2 files now uncovered.

3818 of 4471 relevant lines covered (85.39%)

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