lightcraft/docs/slideshow.md

Slideshow

LightCraft's slideshow follows Lightroom Classic's Slideshow module (no Adobe assets, templates or designs): the photos in view played full screen with a layout, overlays, intro and ending screens and fades, and exported as PDF, JPEG or video. There is no Slideshow module view yet: the settings live in Settings ▸ Slideshow (View ▸ Slideshow Options…) next to a live preview of the selected photo's slide, and View ▸ Slideshow (⌥⌘↩) plays.

Part	Commands	Code
Playback: slide and fade durations, fade colour, random order, repeat, preparing slides ahead	slideshow.playback, view.slideshow	crates/engine/src/slideshow.rs (the timeline), crates/ui-egui/src/panels/slideshow.rs
Layout, options, backdrop: margins, aspect preview, zoom to fill, stroke, shadow, colour, colour wash, background photo	slideshow.layout	crates/slideshow (the composer, no UI), crates/engine/src/slide.rs
Overlays: identity plate, rating stars, text with tokens, watermark	slideshow.overlays	crates/engine/src/slide_overlay.rs
Intro and ending screens	slideshow.titles	crates/engine/src/slide_title.rs
Templates: built-ins of our own and the user's (<settings>/slideshow-templates/*.json)	slideshow.templates.*	crates/engine/src/slide_template.rs
One slide or screen as a PNG	slideshow.preview	crates/engine/src/cmd/slideshow.rs
Export: PDF, JPEG sequence, AV1 video	slideshow.export, slideshow.exportStatus	crates/engine/src/slideshow_export.rs, crates/codecs/src/video.rs

All settings are library preferences (prefs.json); sizes and offsets are fractions of the slide's shorter side, so a slide looks the same on any screen and at any export size. Playback, the preview, slideshow.preview and export draw the same pixels through the same composer.

Export

View ▸ Export Slideshow… (or Export PDF / JPEG / Video at the end of Settings ▸ Slideshow) chooses a format and size, then asks where to write. The slides are the photos in view, in view order, between the intro and ending screens that are on; random order and repeat are playback choices and don't apply. The slide aspect is the Layout's aspect preview (Screen exports 16:9).

• PDF — one page per slide, its picture a JPEG at the chosen quality, the page as many points as the slide has pixels (1024 / 1920 / 3840 on the long side; 64–8192 by command). Each page has the slide duration (/Dur) and, after the first, a fade transition (/Trans), which PDF viewers use in presentation mode; "Automatically show full screen" sets /PageMode /FullScreen. Written by crates/engine/src/pdf.rs (shared with the contact sheet), streamed to disk.

• JPEG — <name>-001.jpg, -002.jpg… in the chosen folder (created; name defaults to the folder's name).

• Video — AV1 in MP4 (default) or WebM, 720p or 1080p (64–2160 by command), 24 or 30 fps (25 / 60 by command), no audio (music is a later item, LRC-SS-MUSIC). The timeline is sampled at the frame rate: a slide's fade-in is rendered frame by frame (a crossfade, or out to the fade colour and in from it), then the slide is held for the rest of its duration as one sample lasting that long (variable frame rate), so a still slide costs one encoded frame. That frame is a key frame: seeking lands on slides. Encoded by rav1e (pure Rust, BSD-2-Clause, already used for AVIF) at speed 10, 8-bit 4:2:0 BT.709 limited range, in order (low latency, no frame reordering); at most 2 hours.

  The muxers are our own (crates/codecs/src/video.rs, from the public ISO/IEC 14496-12 + AV1-ISOBMFF and Matroska/WebM specifications): MP4 is ftyp, one mdat (64-bit size patched at the end) and moov with an av01 sample entry (av1C holding the sequence header OBU, colr nclx, pasp), stts durations, stss key frames and a single chunk; WebM is the EBML header and a Segment with SeekHead, Info (duration), Tracks (V_AV1, CodecPrivate = av1C), Clusters of SimpleBlocks (the last frame a BlockGroup with its duration) and Cues. Samples are temporal units without temporal delimiters. No AV1 decoder is in the product, so the tests check the container structure, sample counts and durations; ffmpeg / browsers play the files (checked by hand when the muxers change).

The export runs on a worker thread with a row in the activity stack ("Exporting slideshow": slides done, or frames for video, and the slide being rendered; ✕ or activity.cancel {id: taskId} stops it). Every output is written as <file>.part and renamed when complete, so a cancelled, failed or interrupted export leaves nothing behind (for a JPEG sequence, all files are renamed at the end). A photo that can't be rendered (its file gone or unreadable) is skipped and named in the result's warnings; a full disk or an unwritable folder is an error. An original in the library is never overwritten (check_write_target before and after).

Encoding speed (rav1e speed 10, measured 2026-10-11 on a 32-thread Linux machine shared with other work): one minute of slideshow (15 slides of 4 s with 1 s fades, 30 fps: 435 encoded frames) took 35 s at 720p and 74 s at 1080p, slide rendering included. The cost is in the fades (one encoded frame per frame of fade); held slides cost one frame each.

Not yet

The Slideshow module view (left-panel template browser, slide editor with draggable guides and overlays), music and sync to music, pan & zoom, H.264 video, saving a slideshow with an album, export presets.