j2k-transcode-metal

Metal acceleration adapter for supported stages in J2K's JPEG-to-HTJ2K coefficient-domain transcode pipeline on macOS.

This crate accelerates supported transform stages and delegates runtime setup to j2k-metal-support.

Auto routing is conservative by default. Single-job reversible 5/3 and 9/7 Metal transcode thresholds are disabled with usize::MAX, so single-tile requests stay on the CPU unless callers explicitly lower with_auto_reversible_min_samples or with_auto_dwt97_min_samples. Same-shape batches use the shared 32-job / 224 * 224 * 32 floors. Auto also avoids the staged 9/7 batch path when either tile axis exceeds 1024 samples; strict Metal requests and caller-lowered thresholds remain explicit policy decisions. These defaults are routing policy, not a speedup promise.

High-level route-report example:

cargo run -p j2k-transcode-metal --example jpeg_to_htj2k_route_report

The example prints the requested backend, selected transform backend, final codestream output backend, structured Auto fallback reason, transfer bytes, and the transcode pipeline residency map.

On macOS, resident_codestream_buffer_from_metal_encoded_j2k converts buffer-backed j2k-metal encode output into the shared ResidentCodestreamBuffer handoff descriptor with allocation and capacity validation.

Links

• API docs: https://docs.rs/j2k-transcode-metal
• Repository: https://github.com/frames-sg/j2k
• Support policy: https://github.com/frames-sg/j2k/blob/main/docs/public-support.md