0014 — Design new slides from the user's own PowerPoint template

• Status: Accepted (2026-10); not yet implemented (roadmap Phase 2c)
• Drivers: users and institutions already maintain a styled PowerPoint (corporate or university template, a Quarto/pandoc reference.pptx). SlideStream's own deck output is a fixed plain layout (ADR-0008), and Presenton (ADR-0009) needs a server, rewrites text and can invent content. A template backend gives the user's exact look, deterministic output, nothing invented, and no second service.
• Related: 0008 (.pptx output), 0009 (--preserve-style render route), 0012 (fallback levels), 0013 (code slides, fidelity).

Context

Two different requests both sound like "reuse my PowerPoint":

The user wants	Answer
Narrate this deck, looking exactly as it does	--preserve-style (exists): LibreOffice → PDF → frames
New content in this deck's style	This ADR: the deck is a template

Pandoc, and so Quarto, already has a convention for the second: --reference-doc reference.pptx. Pandoc ignores the file's slides, takes its slide masters and layouts, and picks layouts by their standard names: "Title Slide", "Title and Content", "Section Header", "Two Content", "Comparison", "Content with Caption", "Blank". These are also the names of the default Office layouts and of python-pptx's built-in template.

Decision

The user's .pptx file is the template, used as it is. SlideStream does not convert it into its own style format. Converting would lose masters, backgrounds, logos, placeholder positions and per-layout differences, and would leave two copies of the style to keep in step.

Only master and layout styling carries over. Formatting applied by hand to individual slides is not part of the template and does not reach new slides. template check says so when a file looks hand-styled.

Layouts are picked by pandoc's names, so an existing Quarto or pandoc reference deck works unchanged:

SlideStream slide	Layout	Filled with
First slide with a title and at most one short line	Title Slide	title, subtitle
Heading only, no content	Section Header	title
Content plus artwork	Two Content	bullets left, picture right
Code block	Title Only	title; code box drawn as in ADR-0013, on the layout's own background
Table	Title Only	title; a native, editable PowerPoint table
Anything else	Title and Content	title, bullets

When a name is missing, use the first layout with the same placeholder types (title plus body, title only); failing that, Blank with SlideStream's own text boxes. Example slides already in the file are removed. Speaker notes carry the narration, as in ADR-0008.

Video frames come from the filled deck, through the existing route: LibreOffice → PDF → pypdfium2 → PNG. The video therefore matches the deck exactly. Slides whose shape differs from the video (for example a 4:3 template in a 16:9 video) are fitted with bars in the slide's own background colour, never cropped or stretched.

Text overflow. python-pptx does not measure text. Estimate the lines each placeholder needs from its size and font size; shrink the body text down to a floor (about 60% of the layout's size); past the floor, keep the slide and report it. Never split a slide, which would break narration alignment.

File types. python-pptx refuses .potx files by content type; load them by rewriting that one content type in memory. .pptx works as is.

Helpers, after Quarto's workflow:

• slide-stream template init my-template.pptx writes a starter template from python-pptx's built-in deck (MIT): widescreen, standard layout names, one example slide per layout. Pandoc's own reference file is not copied.
• slide-stream template check my-template.pptx lists the layouts found, which standard names are missing and what stands in for each, and warns about missing title or body placeholders and slides that look styled by hand.

Interface until roadmap Phase 6: create --pptx-template FILE (and settings.pptx_template). It works for both outputs: .pptx needs only python-pptx; .mp4 also needs LibreOffice. It is separate from --template NAME, which names a Presenton template. Phase 6 folds both into --design.

The plain exporter (ADR-0008) gets the same code-slide and table handling, so all deck outputs show code properly.

Consequences

• Users get their institution's look with no service and no AI rewording; this becomes the local level of the design fallback (ADR-0012), between Presenton and the plain layout.
• Video output with a template needs LibreOffice; deck output does not.
• Quality depends on the template: one with unusual or missing placeholders falls back to simpler layouts, and template check exists to make that visible before a render.
• Fonts the template names but the machine lacks are substituted by LibreOffice in the video frames; the .pptx keeps the original names.
• Tests use small synthetic templates built with python-pptx (standard names, renamed layouts, a 4:3 template, a hand-styled deck); one live test renders frames through LibreOffice when it is installed.