creating-video

Creating Video

Claude cannot render video itself, but it can direct a generator. This skill drives a multi-clip pipeline — script → per-scene generation → review → assembly — with Claude as the editing agent overseeing continuity and cut.

Requires ffmpeg/ffprobe and Cloudflare AI Gateway creds (/mnt/project/proxy.env).

Default model: Gemini Omni Flash (gemini-omni-flash-preview, Interactions API) — Google's own guidance as of 2026-07. It beats Veo on character consistency, reference-image control, text rendering, and conversational editing, and generates faster (~30–90 s/clip vs 1–3 min). Fall back to Veo 3.1 (scripts/veo_generate.py, kept intact) only for scene extension, first+last-frame interpolation, or legacy pipelines — Omni supports neither.

The five stages

1. Shot list — break the story into beats, up to 10 s each, one prompt per shot.
2. Generate — scripts/omni_generate.py, run detached.
3. Review — parsing-video on each clip and on the assembled cut.
4. Assemble — scripts/assemble.py, run detached.
5. Iterate — re-review, then edit failing scenes conversationally (cheaper and more stable than regenerating from scratch).

Stage 2 — Generation (Omni via Cloudflare AI Gateway)

Auth is CF AI Gateway BYOK: proxy.env supplies CF_ACCOUNT_ID, CF_GATEWAY_ID, CF_API_TOKEN; the Google key lives inside the gateway. Both the interactions call and the files/{id}:download retrieval route through it (verified 2026-07-20).

Run detached. The Interactions API is synchronous — the HTTP call holds open for the whole generation (~30–90 s/clip). bash_tool caps at ~50 s. Launch and adaptive-wait on the DONE sentinel:

# prompts.json = {"1": "...", "2": {"text": "...", "images": ["ref0.png"]}, ...}
set -a; . /mnt/project/proxy.env; set +a
(setsid python3 scripts/omni_generate.py prompts.json --out omni/ \
    --negative "on-screen watermark" &)
# then, in a separate call:
timeout 45 sh -c 'while [ ! -f omni/DONE ]; do sleep 3; done'; cat omni/generate.log

Gotchas (all verified 2026-07-20 — the script already handles them):

• No dry run exists. Even input:"" returns 200 and bills a full generation (~58k video output tokens). Every request costs money; never "validate" with a throwaway call.
• No negativePrompt parameter (Veo had one; Omni 400s on unsupported params). --negative folds into the prompt as "Do not include: X."
• Videos >4MB need delivery:"uri" → poll files/{id} to ACTIVE → download via the gateway. The script always uses uri delivery, inline base64 as fallback.
• Output is up to 10 s 1280×720 mp4 with synchronized audio + SynthID watermark. No video extension, no first↔last-frame interpolation, no multi-video referencing — those are Veo territory.
• The egress proxy 503s on cold start → retry with backoff.

Omni defaults to multi-shot. Left alone it invents its own cuts inside a clip, which fights a shot-list pipeline. Every per-scene prompt should say "single continuous shot" / "no scene cuts" unless the beat wants internal cuts.

Stage 3 — Review (use the parsing-video skill)

Contact-sheet each clip and the assembled cut. Per-clip sheets miss cross-clip continuity; the full-cut sheet is where character drift, prop jumps, and logic breaks show up in one read (Oskar, 2026-07-18: review the whole assembly, not just scenes). Scan every sheet against the continuity checklist:

• Character — same face/hair/wardrobe across every shot they appear in.
• Prop — same identity, size, color, and attachment point shot to shot.
• Physical logic — is the world coherent (a window must be open before a bird lands on the sill)?
• Action completeness — is the key action actually shown, not cut around?

Stage 4 — Assembly (scripts/assemble.py)

Trims each clip to its beat, crossfades, drops audio by default, optionally burns an overlay word, and holds the final frame so the ending lands.

(setsid python3 scripts/assemble.py omni/scene_1.mp4 ... omni/scene_6.mp4 \
    --out film.mp4 --tail-hold 1.3 &)

Run detached too — six trims plus a 30 s stitch exceed the bash ceiling on the single-core container. Diagnosed: abrupt ending → --tail-hold; jarring cuts between independently generated ambiences → audio dropped by default (--keep-audio to acrossfade instead).

Stage 5 — Iterate by editing, not regenerating

results.json stores each scene's interaction_id. A failed detail (wrong color, unwanted object, lighting) is a one-line conversational edit that preserves everything else:

python3 scripts/omni_generate.py --edit <interaction_id> \
    "Make the scarf red. Keep everything else the same." --out omni/scene_3_v2.mp4

Simple edit prompts work best; append "Keep everything else the same." Reserve full regeneration for scenes whose composition or action is wrong. (Editing requires store=true, the script's default.)

Prompt craft — continuity is the hard part

The failure modes below came from real crits on 2026-07-18 (Veo era). Omni narrows several of them but the disciplines still pay on the first pass.

• Pin characters and props with reference images — the first-class fix for the drift that text locks never fully solved under Veo. Generate one canonical still per character/prop, put it in the scene's images list, and bind it in the prompt: the woman <IMAGE_REF_0> is holding <IMAGE_REF_1> (refs start at 0; <FIRST_FRAME> pins a starting frame instead).
• Still lock a character sheet in text. One verbatim appearance/wardrobe block, reused in every shot with that character — references constrain, text directs.
• Lock the setting. One room/location description across co-located scenes.
• Name the actor in every shot ("the same woman's hands") — never leave it to the model to infer who is on screen.
• Spell out scene logic — physical coherence, the correct order of beats, and show the payoff action rather than cutting away from it.
• Timing is promptable. [0-3s] ... [3-6s] ... timecode syntax or natural language ("after 3 seconds, ...") controls beats inside a clip.
• On-screen text now renders reliably — spell out exactly what any visible text should say (signs, labels, title cards). Burning text in assembly (assemble.py --overlay-last) remains an option for cross-clip title cards.
• Audio is promptable. Describe the track ("no dialogue", "calm background music") or Omni invents one per clip — which still won't match across clips; assembly drops audio by default for that reason.

Scope

• Transcode / trim / merge / GIF / subtitles → processing-video.
• Reading, summarizing, or QA of existing video content → parsing-video (also the review step here).
• Scene extension / first+last-frame control → the retained Veo path (scripts/veo_generate.py --list to enumerate models; strings drift).