#Downloads And Exports

#Normal ZIP Mode

Downloads are produced by download.ts as golt-export.zip. Normal mode can include:

• .golt saves for first and last selected states.
• Metrics output.
• Indexed PNG frames.
• MP4 video.

Before the download worker starts, the home page pauses the simulation (if running), flushes pending recording frames, waits for required compression, requests a stable snapshot, requests a fresh recording manifest, and then hands both to the worker.

The download worker uses progress bands:

• $0$ to $10$: preparation and ZIP opening.
• $10$ to $55$: streaming save entries.
• $55$ to $85$: recorded frame outputs.
• $90$ to $100$: ZIP finalization.

#Compressed Chunk Mode

Compressed chunk mode is selected when Force chunk download is enabled or the estimated working set exceeds $2\text{ GiB}$. It exports compressed recording chunks instead of rendering the selected outputs. See Compressed chunk export for the standalone file contract and a Python reader example.

The ZIP contains:

• manifest.json: chunk export version, grid size, grid format, selected frame range, and output chunk metadata.
• metadata.json: rules, per-rule probabilities, random seed, tribes, topology, boundary tribe, and recording generation range. Rule and tribe metadata uses the Rule expressions shapes.
• chunks/chunk-000000.bin and following chunk payload files.

Whole selected source chunks are copied. Boundary chunks are rebuilt when the selected range starts or ends inside a source chunk.

#PNG And MP4

PNG export writes indexed-color PNG frames with a palette derived from tribes. Scanlines are streamed through a CompressionStream('deflate'), and row blocks are bounded by a memory budget.

PNG and MP4 visual exports use full-grid framing. When Download is clicked, the home page captures a framing origin and passes it to the download worker. In toroidal topology, that origin is viewport-centered and the worker unwraps each visual frame from it so every grid cell appears exactly once. In bounded topology, the origin is (0, 0), so the finite grid is exported from its top-left corner. This only affects visual frame outputs; .golt saves, metrics, and compressed chunk exports keep the recorded packed-grid order.

Bounded topology does not write virtual boundary cells into PNG, MP4, .golt, or chunk exports. The selected boundary tribe is stored as metadata and affects simulation neighbor reads only.

MP4 export uses browser VideoEncoder support and Mediabunny output writing. Output dimensions are resolved from source grid size:

• Small grids can be uniformly scaled toward a $1080$ reference side.
• Output width and height are clamped to $4096$.
• Minimum output dimension is $3$ before codec-safe even adjustment.
• AVC support is checked before writing, optionally changing the dimensions to support the requested FPS and Bitrate.

The MP4 entry path inside the ZIP is simulation.mp4.

#Working Set Estimate

The download estimator accounts for selected chunks, decompression footprint, previous-frame metrics memory, row buffers, metric entries, and estimated CSV output. Metrics switch to streaming output when retained metric-entry memory exceeds $512\text{ MiB}$. Metrics CSV emits a large-output warning above $512\text{ MiB}$.