wjs-editing-multicam

wjs-editing-multicam

Combine N synced camera angles into a single rendered MP4. Decisions are audio-energy-driven only — the cam with the loudest mic each second wins. Output is hard cuts (or hard cuts plus a corner PiP).

Setup & commands

The implementation lives in the open-source polysync pip package (https://pypi.org/project/polysync/ · https://github.com/jianshuo/polysync) — this skill no longer ships its own scripts. Install it, then drive it via its CLI:

python3 -m pip install -U polysync      # needs ffmpeg/ffprobe on PATH

polysync edit        CAM_A CAM_B CAM_C --out edl.json   # build the decision list
polysync render-cuts edl.json --out out.mp4             # hard cuts
polysync render-pip  edl.json --out out.mp4 --pip bottom-right   # cuts + corner inset

edit and the renderers read each input's .sync.json automatically. Sync first with wjs-syncing-multicam (polysync sync) if the sidecars don't exist yet.

Render flags for raw camera footage (see Preflight below for when to use each):

# Sony S-Log3 footage, shot vertical, FX6 cams turned on their side, for 小红书:
polysync render-cuts edl.json --out out.mp4 \
    --log slog3 \           # S-Log3/S-Gamut3.Cine -> Rec.709 grade
    --rotate 1:90 --rotate 2:90 \   # rotate cam1,cam2 90° CW (FX6 with no flag)
    --width 1080 --height 1920 --fill \   # vertical, crop-to-fill (no black bars)
    --duck-audio --audio-cams 0,1        # clean speaker-gated audio (cams 0,1 = the two lavs)

--duck-audio replaces the single-cam soundtrack with a speaker-gated mix: each moment keeps the active speaker's close mic and ducks the rest (much cleaner than a constant 2-mic sum, which piles up bleed/room tone). --audio-cams 0,1 restricts gating to the real speaker mics — always exclude the wide/room cam, whose mic sits at a similar level but is reverby and would otherwise get picked. (See the editing-quality note below for the why.)

Preflight — ALWAYS check raw footage before rendering (hard-won)