Standalone — Lottie Import, Preview, Render & Export Pipeline

This section documents the standalone animation capabilities of yoAnime Studio — the part that runs entirely on Windows without requiring PowerPoint. Everything described here is handled by the internal WPF application through SkiaSharp, FFmpeg, and custom service layers.

⭐ 1. Overview

yoAnime Studio is a local, offline‑first animation environment designed for importing, previewing, analyzing, and exporting Lottie animations.
The standalone engine consists of:

A Lottie importer (metadata reader + validator)
A preview renderer (Skia/Skottie)
A frame renderer (Skia + optional external CLI renderer)
A transcoder/export pipeline (FFmpeg)
A multi‑job export queue
A project library system
A user‑safe storage architecture

This page explains how each of these components works internally.

⭐ 2. Lottie Import Pipeline

Responsible class: `LottieAssetService`

When a user drops or opens a .json Lottie file, the import workflow does the following:

2.1 File Loading

Reads the JSON file from disk
Streams content to avoid large in‑memory spikes
Computes SHA‑256 hash for caching, deduplication, and re‑export detection

2.2 Metadata Extraction

The importer extracts:

Frame rate (FPS)
Duration
Width & Height
Layer count
Embedded asset references

2.3 Validation Steps

Checks for missing assets (images, fonts)
Detects unsupported Lottie expressions
Flags corrupt JSON

If the file loads successfully, it enters the Project Library with its hash and metadata.

⭐ 3. Real‑Time Preview Pipeline

Responsible class: `SkiaLottiePreviewService`

This component powers the live preview panel you see in the Studio window.

3.1 Skottie Animation Engine

Uses SkiaSharp’s Lottie module (Skottie) for:

Smooth playback
Frame scrubbing
Looping
Zooming
Background color switching
Letterboxing/pillarboxing

3.2 GPU‑Assisted Rendering

Skia creates surfaces in BGRA format
Rendering is DPI‑aware
Output is composited into WPF host controls

3.3 Frame-Accurate Inspection

Every seek or scrub computes a new frame:

Skottie updates the animation time
A new surface is drawn
Frame is converted into a WPF‑friendly bitmap

This enables pixel‑perfect inspection even for high‑resolution animations.

⭐ 4. Frame Rendering Pipeline (Export Path)

Responsible Classes:

SkiaLottieRenderService (in‑process)
ExternalLottieRenderService (CLI‑based renderer)
AnimationRenderStrategy (smart routing)

When the user exports MP4/GIF/WebM, yoAnime must first render individual PNG frames.

4.1 Render Strategy Layer

AnimationRenderStrategy chooses between:

Skia in‑process renderer (default)
External CLI renderer (if configured)

4.2 Skia Frame Rendering

Loads Lottie JSON
Steps through every frame (based on FPS × duration)
Draws each frame to a Skia surface
Saves to numbered PNG files:

frame_00001.png  
frame_00002.png  
frame_00003.png  
...

4.3 External Renderer (Optional)

If an external animation tool is configured:

yoAnime invokes RLottie‑style CLI commands
Collects frames generated externally
Handles temp folder cleanup and error fallback

⭐ 5. Export Pipeline (MP4, GIF, WebM)

Responsible class: `FfmpegTranscodeService`

Once frames are rendered, yoAnime invokes FFmpeg to generate final export formats.

5.1 MP4 Export

Uses H.264 or libx264 encoder
Ensures even-width/even-height video frames
Applies target FPS and bitrate
Allows HD/UHD resolution scaling

5.2 WebM Export

Uses VP9 encoder
Suitable for UI animation workflows
Supports transparency (when configured)

5.3 GIF Export

GIF rendering requires palette optimization:

Generate palette (palette.png)
Use palette during GIF creation
Apply dithering
Optimize frame delays

The pipeline ensures color accuracy while keeping filesize reasonable.

5.4 Pipeline Progress Parsing

FFmpeg progress is parsed from standard output:

Reads timestamps
Maps back to percentage
Emits incremental progress events

⭐ 6. Export Queue System

Responsible class: `ExportJobQueueService`

The job queue enables:

Multiple simultaneous exports
Retry logic
Graceful error handling
Deterministic ordering

6.1 Job Lifecycle

Each export job moves through:

Queued
Rendering frames
Transcoding
Completed
Failed

Jobs are stored with:

File hash
Target format
Timestamp
Output path

6.2 Concurrency

Export jobs run in a background worker
Uses SemaphoreSlim for controlled parallelism
Avoids UI blocking

⭐ 7. Project Library

Responsible class: `AnimationStudioProjectService`

The project library:

Stores metadata of all imported animations
Persists user recents into a JSON file
Validates file existence on re‑launch
Handles corruption detection and automatic repairs
Uses atomic writes to prevent partial file states

7.1 Storage Structure

%LOCALAPPDATA%/yoAnime/yoAnimeStudio/
    projects.json
    samples/
    temp/
    exports/

7.2 What’s Stored Per Project

File path
Hash
Lottie metadata
Export history
Custom names/thumbnails (future feature)

⭐ 8. File Paths & Storage System

Responsible class: `AnimationStudioPaths`

Controls all local directories
Avoids protected system paths
Ensures MSIX compatibility
Creates separate subdirectories per project

Temporary data example:

%LOCALAPPDATA%/yoAnime/yoAnimeStudio/temp/ae4d12fa3/

Export output example:

%LOCALAPPDATA%/yoAnime/yoAnimeStudio/exports/sample_loop.mp4

⭐ 9. Standalone Workflow Summary

Lottie JSON → LottieAssetService → Metadata/Validation
           → SkiaLottiePreviewService → Live Preview
           → AnimationRenderStrategy → Frame Renderer (PNG)
           → FfmpegTranscodeService → MP4/GIF/WebM
           → ExportJobQueueService → Multi‑Job Processing
           → AnimationStudioProjectService → Project Library

This entire workflow runs locally, does not require internet, and does not require PowerPoint.