Odor

A static blog generator built on the muriel filtergraph flow engine. Processes thousands of posts with parallel encoding, incremental builds, and atomic writes.

Quick Start

``bash
npm install odor
odor profile.json
`

Profile Configuration

Odor is driven by a JSON profile. All paths are relative to the profile's parent directory.

`json
{
"profile": "my_blog",
"title": "My Blog",
"src": "database/posts",
"dest": "dist/{profile}",

"theme": {
"src": "themes/my-theme",
"dest": "dist/{profile}"
},

"pagerizer": {
"pp": 24,
"dest": "dist/{profile}"
},

"feed": {
"dest": "dist/{profile}/feed.xml"
},

"cover": {
"dest": "dist/{profile}/permalink/{guid}/cover.avif",
"url": "/permalink/{guid}/cover.avif",
"width": 1024,
"height": 1024,
"quality": 80,
"effort": 4,
"exif": {
"IFD0": {
"Copyright": "Author Name",
"ImageDescription": "Blog Post Cover"
}
}
},

"audio": {
"dest": "dist/audio/chapter-{chapter}/docs/{id}.mp3",
"url": "https://example.com/chapter-{chapter}/{id}.mp3",
"preset": "balanced",
"id3": {
"artist": "Author Name",
"album_artist": "Author Name",
"publisher": "example.com"
}
},

"debug": {
"mostRecent": 32,
"processOnly": ["poem-0001", "poem-0002"],
"skipCovers": false,
"skipAudio": false
}
}
`

$3

| Variable | Expanded from |
|----------|--------------|
| {profile} | profile field in config |
| {guid} | postData.guid from each post's post.json |
| {chapter} | postData.chapter from each post's post.json |
| {id} | postData.id from each post's post.json |

$3

| Field | Effect |
|-------|--------|
| mostRecent | Process only the N most recent posts |
| processOnly | Array of post IDs to process exclusively |
| skipCovers | Skip all cover image encoding |
| skipAudio | Skip all audio encoding |

Post Directory Structure

Each post lives in its own directory under src:

`
database/posts/
poem-0001/
post.json # Required: { guid, id, chapter, title, date, ... }
text.md # Markdown content
cover.jpg # Cover image (jpg, png, webp, or avif)
audio.m4a # Audio file (any ffmpeg-supported format)
files/ # Optional: additional files copied to permalink
diagram.svg
data.csv
`

Flow Graph

`
postScanner -> skipUnchanged -> 'post'

'post' -> [ processCover, processAudio, copyFiles ] -> processText -> verifyPost -> collectPost -> 'done'

'done' -> [ homepage, pagerizer, rssFeed ] -> useTheme -> 'finished'
`

The first edge scans source directories and filters unchanged posts via manifest comparison. The second edge processes each post through parallel encoding (cover + audio + file copy), then series stages for text rendering, verification, and collection. The third edge aggregates all posts into paginated HTML, an RSS feed, and installs theme files.

Transforms

$3

| Transform | Input | Output | Description |
|-----------|-------|--------|-------------|
| post-scanner | filesystem | packets | Reads post directories, emits one packet per post |
| skip-unchanged | packet | packet | Compares against manifest; cached posts bypass encoding |
| process-cover | packet | coverResult | Encodes cover to AVIF via sharp. Copies AVIF sources as-is. Falls back to copy on unsupported formats |
| process-audio | packet | audioResult | Encodes audio to MP3 via ffmpeg with configurable presets |
| copy-files | packet | filesResult | Copies files/ subdirectory contents to permalink |
| process-text | joined packet | textResult | Renders markdown to HTML permalink page |
| verify-post | packet | valid, errors | Checks all results for errors |
| collect-post | packet | side-effect | Pushes to shared processedPosts array for aggregators |

$3

| Transform | Description |
|-----------|-------------|
| homepage | Generates index.html with the latest posts |
| pagerizer | Generates numbered archive pages (page-1.html, page-2.html, ...) |
| rss-feed | Generates feed.xml with the 50 most recent posts |
| use-theme | Recursively copies theme directory (CSS, assets) to dest |

Incremental Builds

The builder maintains .odor-manifest.json in the dest directory. Each post is fingerprinted with a hybrid mtime+hash strategy:

1. Fast path: All file mtimes and sizes match cached values -- skip instantly (zero I/O)
2. Hash fallback: Some mtimes differ -- re-hash only changed files, compare composite hash
3. Rebuild: Composite hash differs or no manifest entry -- full processing

Cached posts emit stored results directly, bypassing all encoding. Aggregators receive identical data regardless of cache status.

Profile changes (detected via config hash) trigger a full rebuild. Already-encoded cover images and audio files are preserved -- only delete the output file to force re-encoding.

Atomic Writes

All file writes use a write-to-tmp-then-rename pattern. If the process is killed mid-write, output files are either fully old or fully new, never corrupt. Stale .tmp files are overwritten on the next build.

Concurrency

Cover encoding (sharp) and audio encoding (ffmpeg) are gated by a shared semaphore limited to os.cpus().length concurrent operations. Sharp's internal thread pool is set to 1 (sharp.concurrency(1)) -- parallelism comes from the semaphore running multiple single-threaded sharp calls. FFmpeg uses -threads 0 (auto).

Audio Presets

| Preset | Quality | Bitrate | Sample Rate | Use Case |
|--------|---------|---------|-------------|----------|
| highQuality | q5 | VBR | 48000 | Archival |
| quality | q6 | 192k | 44100 | High quality |
| balanced | q7 | VBR | 44100 | Default |
| speed | q7 | 128k | 44100 | Smaller files |
| fast | q8 | 96k | 22050 | Minimum size |

Theme

The theme is a directory of static files copied to the dest root. At minimum it should contain a style.css. The HTML templates reference /style.css via a ` tag.

Dependencies

- muriel -- Filtergraph flow engine
- sharp -- Image encoding (AVIF)
- marked -- Markdown to HTML
- ffmpeg -- Audio encoding (system dependency)