Release v1.13.0: timecc608 caption modes, paint-on by default

[tobbee]

Release v1.13.0. The theme is in-band CTA-608 caption modes: timecc608 gains a mode
field and now defaults to paint-on, so a segment's captions no longer depend on its
neighbours. Also bumps mp4ff to v0.55.0 and go-608 to v0.9.0.

Option syntax is now timecc608_<channel>-<lang>[-<mode>[-<modifier>]], e.g.
timecc608_CC1-eng, timecc608_CC1-eng-pop, timecc608_CC1-swe-roll3.

Added

• Optional mode field on timecc608, whose value is now <channel>-<lang>[-<mode>[-<modifier>]], choosing
  the CTA-608 caption mode: paint (the default), pop, pop-sc, roll2 or roll3. Paint-on and roll-up
  type the caption out two characters per frame — paint-on onto a screen cleared at the start of each
  second, roll-up onto the base row of a 2- or 3-row window that scrolls the earlier lines up — and both
  keep every caption inside the segment that carries it, so segments stay independently decodable for a
  client that starts, seeks or joins mid-stream. Roll-up is limited to 2 or 3 rows because the caption's own
  lines put its base row at row 3. Generated by go-608 v0.9.0's generate.BuildUnitPaintCues and
  BuildUnitRollUpCues.

Changed

• timecc608 defaults to paint-on instead of pop-on, so by default no segment's captions depend on its
  neighbours. Pop-on remains available as -pop, with -pop-sc for the self-contained placement; a bare
  -sc (which used to ask for that) is rejected with a message pointing at -pop-sc.
• The timecc608 language must be a three-letter ISO 639-2 code (eng, swe), the form the SCTE 214-1
  CEA-608 accessibility descriptor value is defined in, and the only place this option's language is used.
  RFC 5646 tags that DASH's @lang accepts — en, en-US, zh-Hans — were previously allowed through
  into value="CC1=..." and are now rejected. With the language a single field, an unknown mode or
  modifier is reported instead of being read as part of it.
• mp4ff dependency bumped to v0.55.0 and go-608 to v0.9.0
• The CTA-608 cue scheduling for timecc608 is back to go-608's per-unit builders, whose v0.8.0
  generate.Unit (number, start time and frame count as independent inputs) and WithFlipAtCueStart
  cover both pop-on flip placements livesim2 needs, so the local copy of that scheduler is gone. Same
  bytes on the wire.
• A timecc608 caption cue is never shorter than a second now that go-608 v0.9.0 divides a segment down
  into whole periods: a segment whose duration is not a multiple of a second, e.g. 1.92 s, gets one cue
  covering it instead of two shorter ones. Segments of 2 s and 2.002 s are unaffected.

Fixed

• In-band CTA-608 captions in pop-on mode (timecc608_CC1-eng-pop) are now displayed over exactly the
  interval their text names, instead of appearing 0.6-0.75 s into it. Each cue's flip rides its cue's first
  frame, with the build sent over the preceding frames. Such captions consequently span segment boundaries,
  which costs a client that starts or seeks mid-stream its first cue period — see the
  README. The new default mode, paint-on, has neither problem.

Incompatible changes

Both affect timecc608 URLs only:

• The default mode changed from pop-on to paint-on. Existing timecc608_CC1-eng URLs keep working but
  render differently; add -pop to keep the old behaviour.
• Two-letter and subtagged languages (en, en-US) are rejected — use ISO 639-2 (eng). A bare -sc
  modifier is rejected in favour of -pop-sc.

Release bookkeeping

• internal/version.go: v1.12.0 → v1.13.0, commitDate → 2026-08-11
• CHANGELOG.md: Unreleased entries moved to [1.13.0] - 2026-08-11, Unreleased reset, compare links updated

Verification

go build ./... clean, go test ./... passing, golangci-lint run reports 0 issues.

🤖 Generated with Claude Code