Researched Chrome MV3 offscreen + DISPLAY_MEDIA, MediaRecorder cluster
alignment, SW port keepalive, crxjs offscreen entry, ffprobe verification.
Identified the D-12/D-13 fallback hinge: timeslice=2000ms does NOT force
keyframe alignment (Chrome kf_max_dist=100); Pattern 2 (age-trim) may need
to escalate to Pattern 3 (restart-segments) if ffprobe rejects.
Architecture verified against two in-the-wild production extensions
(Proscreen-S3, meeting_mate) using the exact CONTEXT.md D-01..D-05 path.
The OFFSCREEN_READY handshake (audit P1 #12) and long-lived port keepalive
(audit P1 #8) are wired together. .planning/phases/01-stabilize-video-pipeline/01-RESEARCH.md
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
