The scrubber becomes a layered bar: the native <input type=range> stays
on top for a11y (focus, arrow keys, aria — its track goes transparent
via static page CSS) while the layers beneath render the state:
- Chapter ticks: density-decimated (denseTicks keeps only marks >= 4px
apart) so an 1189-chapter 86-hour book gets ~100 readable marks
instead of a solid mass; the current chapter's tick is tinted.
- Buffered span: the ACTIVE track's buffered-ahead end mapped into the
global bar (buffers are per-track and never span the whole bar).
bufferedAheadEnd reads the range containing the playhead — a huge
m4b's moov index at the file tail is its own buffered range and must
not read as 'the whole book is buffered'. Rides progress + the
events that demonstrably fire for Range-served files that go
network-idle while paused (timeupdate/canplay/loadedmetadata/playing).
- Wheel over the bar: ±5s nudge, Shift = ±60s.
- Hover tooltip: time + chapter title under the pointer.
- Precision rail: while dragging, a ±5-minute window floats below the
bar (fixed anchor; release and re-grab to travel far) and the drag
maps at minutes-per-pixel instead of hours-per-pixel — the whole
point for 80h+ books. Click snaps to a chapter line within ~5s
(snapToChapter).
Pointer handling is ours end-to-end: pointerdown maps hours-per-pixel
+ snaps, captured moves remap through the rail, release seeks. The
native drag default is prevented so the two mappings never fight;
keyboard arrows keep their native step and seek via change.
Time labels get reserved width — the bar no longer resizes when the
elapsed label grows from 0:00 to 43:07 mid-drag (caught by the rail
drag check measuring a 25% mapping drift).
Pure math in audio-scrubber.ts: pointer mapping, chapter lookup, snap,
tick density, per-track buffer→global span, rail window/mapping/ticks.
Unit: 16 new tests including both book shapes (86h/1189ch and
26h/34ch). Live: 23 Playwright checks on KJV (folder) and Gardens of
the Moon (single-file m4b); zip books share the folder manifest shape
(no zip fixture exists in the dev library). Probe user deleted.
John O'Keefe
1f30602c23