screenstudio-alt

The skill's code lives in this directory (polish.py, render.py, studio.py,
events-log.swift, test fixtures, etc.). Published publicly as
connerkward/screen-studio-alternative via the publish-skill skill.

Two components:

• events-log (Swift) — capture-side input logger (cursor 60Hz, clicks, keys;

drops keys during macOS secure input). Runs ONLY while recording. Needs
Accessibility/Input Monitoring for the terminal. **Auto-zoom/keys/cursor need
this data at capture time — it cannot be recovered from pixels later.**

• polish.py (Python, ffmpeg + PIL) — the post-production pass:

python3 src/polish.py in.mp4 --events in.events.jsonl \
  --speedup            # compress idle (input-gap ∩ frozen-pixels; animations stay 1x)
  --zoom               # eased auto-zoom on click clusters (zoompan)
  --keys               # accumulating keystroke chips (PIL overlays, no drawtext dep)
  --smooth-cursor      # synthetic eased cursor (best with sck-record --no-cursor)
  --vertical           # ALSO emit 1080x1920 following the action

--speedup works WITHOUT events (freezedetect only) — usable on the whole
existing dailies corpus.

• render.py — high-quality non-destructive renderer (preferred): single-pass

spring-physics camera over the original high-res frames, LANCZOS into a smaller
target (crisp zoom, ~1.3× sharper than the ffmpeg upscale path), 60fps, H + 9:16 V.
Tunable --freq/--zeta (spring), --fps, --target-w. Takes explicit
--regions [{t0,t1,z,cx,cy}]. polish.py is the older ffmpeg-filter fallback.

• studio.py [recording.mp4] — local web UI, NLE-style fixed-ruler timeline (bar =

source duration, never rescales → upstream always planted): zoom regions are draggable
blocks (move / retime edges / click to add / double-click delete); idle spans are
speed blocks with rate-only editing — source range locked, rate set via inspector
slider on select or right-edge rate-stretch drag (FCP retime / Premiere Rate
Stretch); rate changes ripple downstream only. Tunable cosine-ease ramp, default zoom,
aspect, frame styling. Always-smooth synthetic cursor + click ripple + real recorded
click sound (CC0 #735771). Export uses render.py. Free port, local. (Keystroke overlay
exists in the engine but is off by default.)

Easy path

screencast.sh --demo (screencast skill) does the whole chain: starts the event
logger, records, then polishes + emits the 9:16 vertical automatically. Vertical
is the DEFAULT for social-facing demos.

Gotchas (learned the hard way, kept here so they're not relearned)

• ffmpeg CANNOT do animated scale=eval=frame → crop (link reinit wedges crop's

per-frame exprs). That's why zoom uses zoompan (no t var there — use on/FPS).

• This machine's ffmpeg lacks drawtext; all text/cursor overlays are PIL-rendered

PNGs + overlay.

• Test rig: make-fixture.py synthesizes a fake screen recording + ground-truth

events.jsonl — validate any change against it before trusting real footage.

Limitations

• The workflow assumes FFmpeg plus the companion scripts are available locally; it is not a hosted video editor.
• Polished cursor, click, and keystroke effects depend on event logs captured during recording; missing logs limit what can be reconstructed.
• Auto-zoom and idle speed-up still need human review for pacing, framing, and platform-specific taste.