ADR-005: Parallel frame-range workers and segment concatenation

• Status: accepted · Date: 2026-10-15

Decision

The frame range is split into N contiguous ranges (default: cores − 1). Each worker owns a Chromium process and an ffmpeg process (image2pipe JPEG → x264 CRF 14 veryfast intermediate). Segments are joined with the concat demuxer (stream copy) and the total frame count is verified. A crashed worker is retried once.

Consequences

• Near-linear scaling with cores; memory stays bounded per worker.
• Separate browsers (not tabs) avoid renderer-process sharing that would serialize work.
• Intermediate segments are visually lossless; the final master/share encodes read them once.