readio

readio is a terminal text-to-speech tool. It plans speech with UtterPlan, resolves engine targets, and owns segment synthesis orchestration, AudioCompose timelines, and output. It plays local speech, renders WAV, FLAC, MP3, M4A, Ogg/Vorbis, or Opus files, exports audiobook M4B with embedded chapters, and can publish completed audio through the external save-to-spotify CLI.

Install

python -m pip install "readio[kokoro,cpu]"

For GPU ONNX Runtime:

python -m pip install "readio[kokoro,gpu]"

For the other engines, install readio[piper,cpu], readio[pocket], or readio[kitten]. readio[all,cpu] installs all supported engine packages and optional spaCy planning support for a CPU environment.

Engine adapters may download target and voice assets on first use. Spotify publishing requires the separately installed save-to-spotify executable and its authenticated session. Readio never reads Spotify credential files.

Optional spaCy linguistic planning

Install the optional Utterplan spaCy support when local grammatical annotations are desired:

python -m pip install "readio[spacy]"

Install a compatible local spaCy language model separately. Readio never downloads models implicitly. The default reader.spacy = "auto" tries the best locally installed model and falls back to Utterplan's analyzer when none is available. The explicit sm, md, lg, and trf settings require the selected local model tier and fail if it is unavailable. off disables spaCy analysis.

readio plan stores token annotations and linguistic provenance in the Utterplan schema v3 artifact. Rendering an existing project plan consumes those stored annotations and does not rerun spaCy when the engine, voice, or acoustic settings change. Direct one-shot commands such as readio speak may use the selected engine's local frontend because they do not consume a persisted semantic plan.

Python API

Use readio.api from Python applications for typed synchronous speech, project, catalog, configuration, and diagnostics services. Start with the Python API guide and executable planning example.

CLI help and discovery

readio
readio --help
readio COMMAND --help
readio engines
readio formats

Running readio without arguments shows the command overview. readio engines lists known synthesis engines, and readio formats lists generic audio and audiobook output formats. See CLI reference for help behavior and examples.

Playback

readio speak "Hello from the terminal."
printf '%s\n' "Read this from stdin." | readio speak
readio speak --file notes.md              # parsed as Markdown
readio speak --file notes.md --input-format text  # literal text fallback
readio speak --file notes.md --select last-paragraph
readio speak --file notes.md --select paragraph:3
producer-command | readio speak --live

speak submits synthesized segments to Readio's bounded audio-device queue as they are produced; playback does not wait for the whole document and does not apply whole-program mastering. File rendering remains a separate full-document path that keeps mastering. Both paths share speech synthesis and composition semantics, while Readio owns playback setup and queueing.

A single existing positional token is also treated as a file path by speak, render, and spotify publish, including .ssmd, .ssmd.md, and Markdown files:

readio speak README.md
readio render episode.ssmd -o episode.mp3
readio spotify publish episode.ssmd --title "Episode"

For scripts, prefer the explicit --file PATH form. A missing path-like token fails instead of being spoken as a filename. Use --input-format text to force an existing filename to remain literal text.

In auto mode, filesystem documents are converted to canonical SSMD by ssmdconvert before synthesis. This includes supported text, Markdown, HTML, PDF, DOCX, EPUB, and SSMD files. Explicit --input-format text, markdown, or ssmd forces textual interpretation instead of conversion. Headings, lists, links, images, code blocks, block quotes, tables, task lists, HTML text, and front matter are projected according to the converter; ordinary Markdown remains isolated from SSMD controls.

Auto-converted InputDocument values retain public DocumentProvenance: source format, media type, source name, converter and version, and converter metadata. Explicit text, Markdown, or SSMD input is not mislabeled as converted.

Markdown can also be supplied explicitly through stdin or literal input:

cat README.md | readio speak --input-format markdown
readio render --input-format markdown '# Title' 'This is **important**.'

Use --input-format text when a Markdown-looking file should be read as literal text.

Configuration

Initialize one user-owned Readio configuration and its storage:

readio config init
readio config show
readio config validate
readio config set reader.voice bf_emma
readio roles bind analyst am_michael --engine kokoro
readio config set reader.pause_mode auto

The default configuration uses platformdirs for config, template, ingest, and output locations. READIO_CONFIG overrides the configuration path. New files use schema 3 and canonical engine IDs. v0.3 configuration requires the explicit readio config migrate command; Readio does not silently apply legacy provider fallbacks.

Schema-3 configuration contains reader settings, SSMD validation, paths, language policies, and engine-qualified global role bindings. A role target stores its canonical engine, voice, and optional target_id; provider-specific voice tables are not runtime configuration. Run readio config migrate to convert a v0.3 config explicitly. Templates refer to roles such as host, analyst, guest, and narrator, while literal narration may use reader.voice. Project manifests also use schema 3. Before opening a v0.3 project, run readio project migrate PROJECT; both migration commands preserve a backup and stop on conflicts rather than guessing.

Model discovery and language defaults

Readio uses one registry for kokoro, piper, pocket, supertonic, and kitten; model, voice, and lexicon discovery use the selected engine's catalog and capabilities. Run readio doctor to check whether an engine package and its required public API are available.

Supported engine package floors are PyKokoro >=0.10.2,<0.11, PiperSynth >=0.2.1,<0.3, PocketSynth >=0.2.3,<0.3, SupertonicSynth >=0.1.2,<0.2, and KittenSynth >=0.1.1,<0.2. Each engine package owns its own runtime dependencies; Readio does not require OnnxVoice. Install Kokoro or Piper with a runtime extra such as readio[kokoro,cpu] or readio[piper,cpu], and install Pocket, Supertonic, and Kitten with readio[pocket], readio[supertonic], or readio[kitten]. PDF and DOCX ingestion requires the readio[documents] extra. readio[all,cpu] also installs optional spaCy support.

readio voices list shows runnable voices with semantic references. Canonical engine IDs are kokoro, piper, pocket, supertonic, and kitten; upstream package names such as pykokoro, pipersynth, and supertonicsynth are accepted only as input aliases where applicable. Filters use --engine, --model, --lang, and --gender.

Voice references use SYSTEM:TARGET[/VOICE]: kokoro:v1.0/af_heart, piper:en_US-amy-medium, pocket:english_2026-04/alba, or supertonic:supertonic-3/F1. The system and target identify the engine and model/bundle; the voice suffix is omitted when the target itself is the voice. readio voices show REF inspects one reference. Native voice IDs can be used when discovery context resolves them uniquely; supply engine or target context where the command supports it. References identify voices, while --lang and --gender filter their descriptive metadata.

Kitten can be inspected and selected without changing the other engine workflows:

readio voices list --engine kitten
readio speak --engine kitten --model nano-0.8-int8 --voice Jasper "Hello"

Supertonic targets are discovered from its model catalog. Readio maps locale tags to the engine's base-language key, so en-us is synthesized as en; unsupported language bases are rejected.

readio voices list --engine supertonic --lang en-us
readio render --engine supertonic --model supertonic-3 --voice F1 --lang en-us "Hello"

A Pocket bundle advertising generic en can satisfy --lang en-us; a bundle explicitly advertising en-GB does not. Generic language metadata stays generic and is not assigned unsupported locale specificity. Common --speed is a positive synthesis multiplier, not a composition tempo: Kokoro receives it directly and PiperSynth converts it to length_scale = 1 / speed. PocketSynth supports only 1.0; other explicit values fail validation. Supertonic forwards the multiplier to its atomic synthesis API. --voice-level off|calibrated selects the engine's voice-level handling and participates in speech identity.

Adapters make one strict native synthesis request for each Readio-shaped child and do not invoke native text splitters. Readio owns capacity measurement and exact-text subdivision, preserves linguistic and pronunciation boundaries, and merges child audio and local timings. Unsupported explicit semantics and unsplittable requests fail with stable Readio errors instead of being discarded or truncated.

readio models list --language de --offline
readio models show de-thorsten --offline
readio voices list --model de-thorsten --json
readio models list --preference huggingface --json
readio voices list --model de-thorsten --preference github --json
readio lexicons list --lang de --offline --json
readio lexicons show crane --lang de --offline --json

Piper voice bundles are discovered through PiperSynth without loading ONNX during planning:

readio voices list --engine piper --lang de
readio voices list --model piper --lang de
readio voices list --engine piper --model de_DE-thorsten-medium --lang de
readio render --engine piper --voice de_DE-thorsten-medium --lang de --dry-run --json "Hallo Welt"
readio speak --engine piper --voice de_DE-thorsten-medium --lang de "Hallo Welt"
readio render --engine piper --voice de_DE-thorsten-medium --lang de --manifest -o article.wav "Hallo Welt"
readio render --engine pipersynth --voice de_DE-thorsten-medium --lang de --dry-run --json "Hallo Welt"

Pocket targets are bundle IDs. --voice selects a bundle's predefined voice, --voice-file uses a local reference WAV, and --voice-prompt selects a managed Kyutai prompt. These selectors are mutually exclusive. Tune only the Pocket-specific generation controls you need:

readio voices list --engine pocket --lang en-us
readio render --engine pocket --model BUNDLE_ID --voice VOICE --precision int8 "Hello"
readio render --engine pocket --model BUNDLE_ID --voice-file reference.wav --temperature 0.6 --lsd-steps 3 "Hello"
readio voices prompts --engine pocket --dataset alba
readio voices prompts --engine pocket --variant casual --license cc-by-4.0
readio render --engine pocket --model BUNDLE_ID --voice-prompt kyutai-tts-voices:alba-mackenna/casual --temperature 0.6

Local reference voice files are user or project assets. Readio records their content hash in readio.plan.v2; local paths are not included in acoustic render identity. Managed Pocket prompts are catalog assets: plans pin the prompt reference, SHA-256, source revision, and available provenance. Pocket verifies prepared provenance and records its normalized-audio fingerprint separately from the source hash. This selector applies to the default synthesis voice, not per-role bindings. Piper's published text API does not accept Readio token or pronunciation annotations, so explicit pronunciation directives are diagnosed instead of silently discarded.

Use --speaker NAME_OR_ID for a multi-speaker Piper bundle. Live rendering depends on the selected engine's declared capability.

Use --refresh to refresh registry metadata only. --offline --refresh is invalid. Offline metadata requires a cached registry; offline synthesis additionally requires cached model and voice assets.

Persist a validated default per language. Language keys are normalized, and locale-specific profiles fall back to their base language:

readio defaults set de --model de-thorsten --lexicon crane --offline
readio defaults show de --json
readio defaults show de-at --json
readio render --lang de --file notes.md

When a model is selected, Readio fills its normalized source, default voice, and preferred quality, then validates language compatibility, voice roster, quality, named lexicons, and experimental frontend permission before saving. --no-lexicons selects explicit provider-only pronunciation (lexicons=[]); --auto-lexicons returns to engine language defaults (lexicons=null). Repeat --lexicon to preserve ordered layered lookup. Readio owns pause placement. Its pause_mode defaults to auto; tts leaves natural sentence timing to the engine, while manual uses explicit semantic boundary pauses. A persisted reader.pause_mode remains the default for that installation. Named lexicons use engine selectors, not backend asset IDs: crane = named selection token de-de:crane = language-qualified Lexphon asset resolved downstream de-crane = separate acoustic model ID

For reproducible German synthesis:

```bash
readio models show de-thorsten
readio defaults set de --model de-thorsten --lexicon crane --g2p-fallback espeak --lexicon-data-policy auto
readio render --file article.md --lang de --dry-run --json
readio render --file article.md --lang de --model de-thorsten --no-lexicons --g2p-fallback espeak --format mp3

The plan also records optional PyKokoro language detection. SSMD documents may use language_detection: {mode: auto, languages: [de, en]}; this routes pronunciation fragments while retaining the selected acoustic language.

Templates

Built-in templates are copied into the user template directory during initialization. They are user-owned and are not overwritten by normal initialization or package upgrades.

readio template path
readio template list
readio template show podcast
readio template add custom --file custom.ssmd
readio template remove custom
readio template reset podcast
readio template reset --all

Create an agent-editable draft with an automatic filename:

draft="$(readio template use podcast)"

The returned path is under the configured ingest directory. A caller can request a filename with readio template use podcast --name weekly-review.ssmd.

Standalone LLM authoring guides

llm-guides/ssmd/ contains standalone Markdown instructions for generic LLMs. These guides are distinct from the runtime .ssmd templates managed by readio template.

No Readio or Python installation is needed on the authoring system: choose one guide and attach it with the task and source material. When the harness supports artifacts, ask it to create and return one downloadable .ssmd.md file; otherwise save the raw SSMD response as a .ssmd.md file. Readio also accepts .ssmd for compatibility. Rendering and final validation happen later on a system where Readio is installed.

See llm-guides/README.md for the catalog and the authoring-to-rendering workflow.

Ingest directory

The ingest directory stores text, Markdown, and SSMD files created for later processing.

readio ingest path
readio ingest new
readio ingest new --name notes.txt
readio ingest new --template podcast --name episode-42.ssmd
readio ingest list

Automatic names contain a UTC artifact ID such as 20260824T111423Z-5f8ab31c. Explicit names are relative to the ingest directory and path traversal is rejected.

Planning before rendering

Every non-live readio render resolves an explicit synthesis plan before TTS work. Use readio render --dry-run to inspect the same plan without loading a model; a normal render executes exactly the plan it resolved:

readio render --file episode.ssmd --format mp3 --dry-run --json
readio render --file episode.ssmd --dry-run          # human output
readio render --file episode.ssmd                    # resolves the same plan, then executes it

Planning, discovery, defaults, and render results are distinct layers:

• readio models / readio voices (discovery) list what the installed engine runtime could provide — model IDs, languages, voices, qualities, lexicons, status.
• readio defaults (defaults) persist validated per-language policy that resolution prefers.
• readio plan (project planning) builds semantic plans for persistent projects and provides roles, bind, and unbind for project-local SSMD cast settings. It does not resolve one-shot engine/model/output choices or load TTS.
• readio render (render result) executes the plan; the plan JSON's synthesis, SSMD bindings, and output path are the values actually used. A render that fails planning exits 1 with the plan and its diagnostics instead of loading TTS.

readio.plan.v2 JSON exposes schema, ok, input, planning, semantic_plan, render (with engine-neutral target), output (format, encoder backend, path, path origin, force), environment (generic package versions), decisions (winning source per field), and diagnostics:

{
  "schema": "readio.plan.v2",
  "ok": true,
  "operation": "render",
  "input": {
    "source_path": "article.md",
    "source_kind": "file",
    "requested_format": "markdown",
    "format": "markdown",
    "source_sha256": "...",
    "selector": "all"
  },
  "planning": { "language": "de", "unit": "sentence", "pause_mode": "auto" },
  "semantic_plan": {
    "format": "utterplan",
    "schema_version": 3,
    "plan_id": "...",
    "sha256": "...",
    "path": "plan/document.utterplan.json"
  },
  "render": {
    "engine": "piper",
    "target": {
      "id": "de_DE-thorsten-medium",
      "language": "de",
      "voice": "thorsten"
    },
    "rate": 1.0,
    "options": { "ssmd_voice_bindings": { "narrator": "thorsten" } }
  },
  "output": {
    "mode": "file",
    "format": "mp3",
    "encoder_backend": "soundfile",
    "path": ".../article.mp3",
    "path_origin": "explicit",
    "force": false
  },
  "environment": { "packages": {}, "ffmpeg_available": true },
  "decisions": [
    {
      "field": "ssmd.bindings.narrator",
      "origin": "cli",
      "locator": "request.voice_bindings"
    }
  ],
  "diagnostics": []
}

One-shot planning is deterministic and non-interactive. Use repeatable --voice-bind ROLE=VOICE_ID options for invocation-only choices or persist project-local role choices with readio plan bind; --resolve-voices is rejected by render --dry-run.

Durable render manifests

For bounded renders that will be reused, published, compared, or handed to another agent, request an opt-in post-render manifest:

readio render --file episode.ssmd --format mp3 --dry-run --json
readio render --file episode.ssmd --format mp3 --manifest
readio render --file episode.ssmd --format mp3 --manifest --json

A successful render writes the audio and a colocated <audio>.readio.json sidecar. The sidecar uses schema readio.render-manifest.v2 and records the exact executed readio.plan.v2, its canonical SHA-256, the semantic plan identity, the final encoded audio hash and byte count, render summary facts, document metadata, and final marker offsets. The plan is pre-execution intent; the manifest is post-execution evidence.

Human stdout remains only the audio path. JSON render output remains one object and adds manifest with the sidecar schema and path, or null when the flag is absent. --manifest is available only for bounded rendering, not --live, speak, planning, dry runs, or publishing. If sidecar writing fails, Readio preserves the committed audio and returns render.manifest_error.

Multi-format audio output

The output path is optional and WAV remains the default:

readio render "Hello from a file."
readio render --file "$draft" -o episode.wav
readio render "Hello" -o episode.mp3
readio render --file episode.ssmd --format m4a
readio render "Hello" --format ogg

Project exports support lossless FLAC and Opus in addition to the existing formats:

readio export project.readio --format flac
readio export project.readio --format opus --bitrate 96k

.ogg remains Ogg/Vorbis; .opus selects Opus and is a separate format. Readio's generic Opus default is 96k; this is Readio's setting, not a claim of TTSForge default parity.

Progress

render, synth, preview, compose, project render, and spotify report low-noise progress on stderr. It is enabled automatically on an interactive terminal. Use --progress to force it or --no-progress to suppress it:

readio compose manuscript.readio
readio compose manuscript.readio --progress
readio compose manuscript.readio --no-progress
readio compose manuscript.readio --json --progress
readio render --file episode.ssmd -o episode.mp3 --progress
readio spotify publish --file episode.ssmd --title "Episode" --json

Composition progress shows the current speech segment, active operation, completed and total segments, elapsed time, and an approximate ETA after enough segment work has completed. The ETA covers segment processing only. Assembly, complete-output loudness and true-peak processing, and composition artifact writing are shown as separate final stages.

--json keeps stdout to one machine-readable result object. Progress remains on stderr, automatic progress is disabled in JSON mode, and explicit --progress remains stderr-only. Verbose mode uses line-oriented stderr output instead of in-place terminal rewriting.

Verbose diagnostics

Use the global repeatable verbosity option for live operational diagnostics:

readio -v speak "Hello"
readio -vv render episode.ssmd -o episode.mp3
readio speak "literal --verbose" --

-v shows timestamped lifecycle records at INFO level. -vv enables DEBUG-level Readio and selected engine details; additional repetitions are clamped to DEBUG. Verbose records always go to stderr, so ordinary output and --json results remain on stdout and stay machine-parseable. --progress is a separate user-facing progress control. When verbose mode and progress are combined, progress uses line-oriented stderr records instead of in-place terminal rewriting. Logs can contain paths and model or voice identifiers, so review them before sharing and never treat verbose mode as permission to expose document text, audio, or credentials. When -o is supplied, .wav, .flac, .mp3, .m4a, .ogg, and .opus suffixes select the corresponding render encoder. .ogg means Ogg/Vorbis; .opus is distinct. Use --format when the output path is omitted or to select the automatic filename suffix. An explicit format and suffix must agree. Extensionless output paths receive the selected suffix, and unsupported suffixes fail before synthesis. Automatic names use the configured output directory and never overwrite an existing file. Explicit output remains atomic and requires --force for replacement.

M4A and Opus require an ffmpeg executable on PATH. WAV and FLAC use PCM16; MP3 and Ogg/Vorbis use the installed SoundFile/libsndfile codecs.

SSMD consumption and authoring checks

For .ssmd and .ssmd.md inputs, Readio compiles SSMD through UtterPlan once, resolves document-local voice_bindings and missing invocation or configured roles, then lowers semantic segments to neutral engine requests. Document bindings remain authoritative, and unsupported explicit semantics fail before a synthesis session opens. Normal speak, render, and spotify commands do not rewrite source SSMD.

Readio accepts SSMD 0.9.x and UtterPlan 0.3.x/schema v3 only. SSMD 0.8 syntax, raw <div> directives, and legacy prosody aliases are rejected, not rewritten or migrated. Existing project plans using UtterPlan schema v1 or v2 are stale and must be rebuilt from valid SSMD 0.9 or plain text. This does not change Readio's own readio.plan.v2 response schema.

Inspect a document before rendering:

readio ssmd check episode.ssmd
readio ssmd check episode.ssmd --json
readio ssmd check episode.ssmd --roundtrip

readio template validate --all checks shipped or configured templates with the same consumer preflight. Add --roundtrip for strict SSMD authoring validation. Unknown logical roles fail before model inference with a Readio diagnostic.

Spotify publishing

Publishing is explicit and uses the clean command family:

readio spotify publish --file "$draft" --title "Weekly Review" --format mp3 --wait
producer-command | readio spotify publish --live --title "Live episode" --format mp3
readio spotify upload recording.m4a --title "Lecture 3" --show-id spotify:show:abc --wait 2m
readio spotify shows --json
readio spotify status spotify:episode:abc --wait
readio spotify doctor --json

Publish renders and uploads Readio source. Direct upload starts from caller-owned WAV, MP3, M4A, or OGG and never deletes or overwrites it. Without --output, generated publish media is temporary and deleted after success or failure; with --output, it is retained. --chapters-from-markers and caller-owned --timeline FILE are mutually exclusive, and either timeline path waits for READY before publishing. --wait optionally accepts a duration; --wait-timeout is deprecated. --api-timeout controls an upstream request separately from readiness waiting.

spotify publish --live reads plain-text stdin and leaves live rendering, engine capability checks, and temporary audio-file ownership to the application services. Without --output, generated audio is temporary and removed after success or failure; with --output, the file is retained.

Readio invokes save-to-spotify --json, reports its detected version in diagnostics, and does not inspect credentials, expose tokens, or perform authentication.

Doctor

readio doctor

Doctor is offline/local by default and supports readio doctor --json. It reports Readio configuration, directories, TTS/SSMD dependencies, audio formats, and the upstream save-to-spotify path/version probe. It does not authenticate, inspect credentials, or perform Spotify network operations; use readio spotify doctor for the explicit external integration check.

Agent Skill

The portable skill is in skill/readio/SKILL.md. It uses Readio templates and commands directly. It does not teach raw SSMD voice discovery, create, lint, temporary file management, or manual cleanup for normal podcast workflows.

SSMD voice resolution and project role targets

Document-local SSMD bindings retain the provider-qualified voice_bindings syntax. They keep a portable document's speaker choices with the source:

voice_bindings:
  kokoro:
    moderator: af_sarah
    architect: am_michael

SSMD syntax is unchanged. A role bound in more than one provider namespace in the same document is ambiguous; Readio reports an error rather than selecting one. Resolution precedence is document binding, invocation --voice-bind, project role target, global configured role, then a direct semantic reference or context-resolved native voice ID. Document bindings remain authoritative.

Discover runnable voices with readio voices list --json or filter with readio voices list --lang de. Semantic references replace numbered voice selectors. For example, bind Kokoro with kokoro:v1.0/af_heart and Piper with piper:en_US-amy-medium. Persist global roles with readio roles bind ROLE REF; use --engine ENGINE for a native voice ID when its engine cannot be inferred, and prefer a semantic reference when its target must be explicit. readio roles list reports engine-qualified targets. v0.3 [voices.<provider>.roles] settings are converted only by the explicit readio config migrate command; normal runtime code does not read them.

For deterministic one-run automation, use repeatable --voice-bind ROLE=REF options. Readio resolves semantic references to engine-qualified targets; document bindings continue to take precedence:

readio render --file episode.ssmd \
  --voice-bind moderator=kokoro:v1.0/af_sarah \
  --voice-bind architect=kokoro:v1.0/am_michael

--resolve-voices prompts only when explicitly requested from an interactive TTY. It never persists choices. JSON, agents, scripts, and non-TTY execution must use --voice-bind. readio ssmd bind FILE --voice-bind ROLE=VOICE_ID -o OUTPUT.ssmd explicitly materializes bindings into a new source file; ordinary consumption never edits SSMD.

Project-local role targets let one SSMD document use multiple synthesis engines without changing the semantic SSMD speaker references:

cd episode.readio
readio plan bind host kokoro:v1.0/af_sarah
readio plan bind guest piper:en_US-amy-medium
readio plan roles
readio plan
readio synth

New bindings are stored role-centrically in project.json under settings.ssmd.role_bindings, with each target's engine, canonical voice, and optional target_id. Selector provenance is not persisted. Binding a semantic reference retains its structured engine and target identity and does not set a project-wide provider. Use readio plan bind ROLE REF PROJECT or --project PROJECT from outside the project; nested working directories are discovered. For native voice IDs, pass --engine when needed and use a semantic reference if the target is ambiguous.

v0.3 manifests with settings.ssmd.voice_bindings require explicit readio project migrate PROJECT; normal project reads do not fall back to provider-keyed data. After migration, settings.ssmd.role_bindings supports multiple engines without a project-wide provider. Use readio plan roles --engine ENGINE to filter inspection.

readio plan bind does not rewrite SSMD or change the semantic plan ID. It changes acoustic synthesis settings, so readio status leaves planning current and reports synthesis stale; run readio synth to refresh it. Synthesis routes bound segments through each target's engine and uses the normal project synthesis selection for unbound segments. Engines and sessions are resolved per route, so a mixed-engine project does not require one project-wide provider.

Persistent incremental projects

For resumable builds, create a project and use explicit stages:

readio project init manuscript.md -o manuscript.readio
cd manuscript.readio
readio plan                         # semantic only; no TTS
readio preview manuscript.readio --select first:3 --voice de-ko-01 -o preview.wav
readio synth manuscript.readio --voice de-ko-01
readio compose manuscript.readio --target-lufs -18
readio export manuscript.readio --format mp3
readio status manuscript.readio --json
readio render manuscript.readio --format mp3  # build stale stages

Chapter-aware audiobook projects accept EPUB files and .ssmdbook directories or .ssmdbook.zip bundles produced by ssmdconvert. EPUB and ZIP inputs are materialized as standalone editable .ssmdbook directories. Readio attaches disposable project state under .readio/ and indexes the canonical chapter files in place instead of copying them.

readio audiobook chapters novel.epub
readio audiobook init novel.epub --chapters 2-20
readio audiobook chapters novel.ssmdbook.zip
readio audiobook init novel.ssmdbook --chapters 3-4,7
cd novel.ssmdbook
readio plan roles
readio plan
readio synth --voice en-ko-01
readio compose
readio export --format m4a
readio audiobook export . --format m4b --cover cover.jpg
# Or build all stale stages with:
readio render novel.ssmdbook --format m4a

Chapter selectors use the available 1-based source chapter numbers reported by readio audiobook chapters and preserve source order, including non-contiguous bundle subsets. Edit canonical chapter files under chapters/ (or paths listed in manifest.json). Readio reads edits immediately, refreshes only its local index, and replans/resynthesizes affected content. After chapter edits, run ssmdconvert book refresh novel.ssmdbook to update canonical manifest hashes; Readio never does this automatically. Deleting .readio/ removes local plans, caches, and outputs but leaves the editable book intact; readio audiobook init novel.ssmdbook can recreate that state. Generic EPUB rendering remains one combined document, so use audiobook commands for chapter-aware processing.

Audiobook projects can be exported as M4B with embedded chapters: readio audiobook export . --format m4b. Title and author default from the book's metadata and can be overridden with --title and --author. Readio's AAC bitrate default is 192k; use --bitrate to choose another supported bitrate.

Cover art is explicit-only: pass --cover cover.jpg or a PNG path. Readio validates, hashes, attaches, and tracks the image. Automatic source cover extraction is not part of the current ssmdconvert integration; provide a JPEG/PNG cover explicitly. M4B is audiobook-only; generic readio export supports WAV, FLAC, MP3, M4A, Ogg/Vorbis, and Opus, never M4B.

See docs/projects.md and docs/incremental-rendering.md for the project layout, cache identities, status diagnostics, and invalidation matrix. Project synthesis, composition, and export defaults can be saved before execution with readio project settings set PROJECT ...; inspect with readio project settings show PROJECT --json. Requestless project operations use saved settings, while explicit invocation overrides remain transient. Audiobook M4B output, metadata, cover, and bitrate can also be saved and are checked by readio status. See project settings, CLI reference, and Python API.