SB3 to MP4 Converter

Purpose & User Intent: This tool solves the problem of turning Scratch 3 SB3 project files into standalone MP4 videos for playback outside the Scratch environment. Primary users are educators, content creators, and developers who need portable demos, lesson recordings, or asset previews. It is used when a shareable, offline video representation of a Scratch project is required, for archiving, assessment, or publishing.
Core Logic & Features: The tool accepts SB3 files (ZIP containing project.json and assets) and renders a linear video sequence by simulating the project timeline at a user-selected framerate. Required features: SB3 ingestion, MP4 output, framerate, resolution. Optional/advanced: audio inclusion, multiple resolution presets, batch processing, and naming templates. Unique differentiators: headless Scratch-like rendering with deterministic frame capture, support for transparency, and consistent export across sessions. Use cases: classroom demos without interactive runtime, animated summaries of projects, or teacher tutorials.
Inputs & Outputs: Inputs include: sb3_file (File, required), target_resolution (width x height in pixels, required), framerate (fps, integer, required), include_audio (boolean, optional, default true), output_name (string, optional). Outputs: mp4_file (video, MP4), duration (seconds), actual_framerate (fps), final_resolution (width x height). Validation: SB3 file must be a valid ZIP with project.json; resolution must be within 320x240 to 3840x2160; framerate between 1 and 60.
Algorithms & Calculations: Process steps: unzip SB3; parse project.json; map sprites to layers; render each frame at frame_index, capturing stage and sprite positions; encode frames to MP4 using H.264/AAC; duration = total_frames / framerate; optional audio is embedded if present in assets and enabled. Edge cases: missing assets or invalid JSON triggers failure; extremely large SB3 may trigger timeouts; unsupported features (custom extensions) degrade to static preview.
Industry/Region & Localization: Output MP4 adheres to ISO/IEC standards; uses H.264 video and AAC audio; supports internationalized filenames and metadata; unit is pixels for resolution; no currency.
Assumptions & Exclusions: Assumes SB3 is a valid Scratch project with accessible assets; does not execute interactive input or real-time user events; no live network fetches during conversion; excludes exporting UI elements or Scratch runtime state beyond video frames; licensing and asset permissions are responsibility of user.