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Video generation

Sesi can generate an MP4 with the Gemini API through its AI form of video():

video(model) {config} {prompt}

The expression returns the MP4 as a Base64 string. Write it with

write_file(path, value, "base64"). This is different from the local-media

form, video(input, output, options?), which uses FFmpeg to create or

transcode a video.

Keep the configuration and prompt contents on one physical line. In Sesi,

newlines inside these video() blocks are statement separators.

Video generation is a remote, billed operation. It requires GEMINI_API_KEY,

can take from seconds to minutes, and should be written to disk immediately

with failure handling.

let output = "generated_media/clip.mp4"
let prompt = "A tiny glass robot walks through a rain-soaked neon garden, cinematic tracking shot, soft rain and distant city ambience"

let clip = video("gemini-omni-flash-preview") {ratio: "16:9"} {prompt}
output | write_file(clip, "base64")
show "Saved" output

See the runnable example.

Choose a model

Use case	Model	Sesi API behavior
Fast generation and image-guided clips	`gemini-omni-flash-preview`	Calls Gemini's synchronous Interactions API.
Cinematic Veo output, including 4K	`veo-3.1-generate-preview`	Starts and polls a long-running Veo operation.
Lower-latency Veo preview	`veo-3.1-fast-generate-preview`	Same Veo operation workflow.
Cost-conscious Veo preview	`veo-3.1-lite-generate-preview`	Same workflow; 4K and video extension are unavailable.

All of these model IDs are previews, so availability, pricing, quotas, and

capabilities can change. Do not use the deprecated Veo 3.0 or Veo 2 IDs in new

work.

Sesi configuration

The configuration block accepts these aliases. Unknown keys are ignored by the

Sesi video runtime.

Sesi key	Aliases	Applies to	Gemini API field / notes
`ratio`	`aspectRatio`, `aspect_ratio`	Omni, Veo	`"16:9"` (default) or `"9:16"`.
`images`	`image`	Omni, Veo	A path or array of local reference-image paths. Omni sends every supplied image; the current Veo wrapper sends the first only.
`task`	—	Omni	One of `text_to_video`, `image_to_video`, `reference_to_video`, or `edit`. Usually omit it and let the model infer the task.
`duration`	`durationSeconds`, `duration_seconds`	Veo	`4`, `6`, or `8` seconds. Use `8` for 1080p/4K.
`resolution`	`size`	Veo	`"720p"` (default), `"1080p"`, or `"4k"`; Lite does not support 4K.
`poll_interval`	`pollInterval`	Veo	Milliseconds between operation checks; defaults to 10,000 and is clamped to at least 100.
`negative_prompt`	`negativePrompt`	Veo only	Passed to Veo. Omni does not support this control; put exclusions in the prompt instead.
`audio`	`generateAudio`, `generate_audio`	Veo only	Passed through for model variants that support it. Veo 3.1 natively generates audio, and Omni generates video with audio.

Veo: text to video

let clip = video("veo-3.1-generate-preview") {ratio: "9:16", duration: 8, resolution: "1080p", poll_interval: 10000} {"Vertical tracking shot of a red paper boat drifting down a rain-filled city gutter at night; neon reflections, shallow depth of field, gentle rainfall and distant traffic ambience."}

"generated_media/veo.mp4" | write_file(clip, "base64")

Veo 3.1 produces 24-fps video with native audio. Higher resolutions cost more

and typically take longer. Veo requests are asynchronous in Gemini; Sesi polls

them until complete before returning the Base64 MP4.

Omni: image to video

let clip = video("gemini-omni-flash-preview") {images: "assets/product.png", ratio: "16:9", task: "image_to_video"} {"Bring this product shot to life on a clean studio tabletop. Slow orbiting camera move, soft natural shadows, no text overlays."}

"generated_media/product.mp4" | write_file(clip, "base64")

Omni takes text or text plus local images and returns the completed result from

the Interactions API. It is well suited to quick iterations and image-guided

generation.

Prompting

State the subject, setting, action, visual style, camera movement, lighting,

mood, and desired sound when it matters. Describe audio directly rather than

assuming a soundtrack or dialogue.

Wide shot: a brass automaton repairs a small sailboat in a foggy harbor at dawn.
The camera slowly dollies from the dock toward the boat. Warm lantern light,
muted teal fog, hand-crafted stop-motion texture. Wood creaks, water laps, and
the automaton quietly hums; no captions or logos.

For Omni, express negatives in normal prompt language, such as “no captions or

logos.” Its API does not support a separate negative-prompt parameter.

Current Sesi scope

Sesi intentionally exposes the common generate-from-text and generate-from-image

paths. The following Gemini capabilities are not represented by video() yet:

Omni stateful editing with previous_interaction_id, uploaded-video editing,

URI delivery, and background/stream controls.

Veo video extension, first/last-frame interpolation, and up to three Veo

reference images.

Veo controls such as seed and person-generation settings.

For those workflows, call the Gemini API directly with the current

@google/genai SDK. In particular, retain an Omni interaction ID if you need

conversational edits; Sesi returns only the generated video data.

Operational and safety notes

Download or save a Veo result promptly. Gemini documents a two-day server

retention period for generated Veo videos.

Do not rely on multi-video prompting: both model guides warn that reasoning

across multiple video inputs is unsupported or can degrade results.

Generated videos are SynthID watermarked. Gemini safety filters apply to the

prompt and output, and regional restrictions apply to some people and media

editing cases.

Omni is preview-only. It does not currently support audio references, voice

editing, video extension, or interpolation. Some uploaded-image/video editing

functionality is unavailable in the EEA, Switzerland, and the UK.