FastVideo Interleave Example

This directory contains a small Python example for running an application-level InterleaveThinker-style image generation trace on top of FastVideo. The helper code lives under fastvideo/workflows/interleave_thinker and is importable as fastvideo.workflows.interleave_thinker.

Single-Prompt Trace

Run:

FASTVIDEO_ATTENTION_BACKEND=TORCH_SDPA \
  python examples/interleave/interleave_single_prompt.py \
    --model-path black-forest-labs/FLUX.2-klein-4B \
    --prompt "a brushed steel espresso machine on a marble counter, morning window light" \
    --output-dir outputs/interleave_single_prompt

The script uses VideoGenerator directly through the local FastVideo image backend. It writes the generated image and a trace.json file under the output directory. The trace records the generation attempt and omits base64 image payloads by default.

How The Example Planner Works

SinglePromptPlanner is intentionally minimal: it takes the user instruction and creates one generation step with that exact prompt. It does not decompose the instruction, call a learned planner, or create multiple edit steps.

AcceptAllCritic is equally small. It accepts the first generated image, so the example can produce a complete trace without requiring a learned critic model. The orchestration code still records the planner, generator, and critic result so a trace has the same shape when a richer app-specific planner or critic is added later.

Optional Gemini Backends

The app helper can also use closed-source Google image models through lazy wrappers when you instantiate the backend directly:

fastvideo.workflows.interleave_thinker.generator.NanoBananaImageGeneratorBackend implements the same image backend protocol as the local FastVideo generator.

Install the optional SDK and provide a key only when using these API backends:

uv pip install -e ".[eval-judge]"
export GEMINI_API_KEY=...

Supported Nano Banana aliases are:

nano-banana -> gemini-2.5-flash-image
nano-banana-pro -> gemini-3-pro-image
nano-banana-2 -> gemini-3.1-flash-image