Multimedia Backend Integrator

Reference guide for adding new media generation backends to MassGen's unified generate_media tool.

Architecture Overview

_base.py          -- Registration: API keys, default models, priority lists
_selector.py      -- Auto-selection logic: picks best backend by key + priority
_image.py         -- Image backends: OpenAI, Google (Gemini/Imagen), Grok, OpenRouter
_video.py         -- Video backends: Grok, Google Veo, OpenAI Sora
_audio.py         -- Audio backends: ElevenLabs, OpenAI TTS
generate_media.py -- Entry point: routing, validation, batch mode, image-to-image

Complete Checklist: Adding a New Backend

1. Registration (_base.py)

• Add to BACKEND_API_KEYS: map backend name to env var(s)
• Add to DEFAULT_MODELS: map backend name to {MediaType: model_name} for each supported type
• Add to BACKEND_PRIORITY: insert at correct position per media type

2. Implementation (_image.py / _video.py / _audio.py)

• Add import for SDK at module top
• Implement _generate_{media}_{backend}(config) -> GenerationResult
• Check API key first, return error result if missing
• Create SDK client with API key
• Map config.* fields to SDK parameters
• Handle continuation (if applicable) — see Continuation Store Patterns
• Write output bytes to config.output_path
• Return GenerationResult with metadata
• Wrap in try/except, log errors

3. Dispatcher Update

• Add elif backend == "new_backend": in the media type's generate_{media}() function

4. Image-to-Image Support (generate_media.py)

• Add backend name to the selected_backend not in (...) check in _generate_single_with_input_images
• Add fallback: elif has_api_key("new_backend"): in the auto-selection chain
• Update error message to mention new backend + env var

5. Documentation

• TOOL.md: Add env var to frontmatter, backend to tables, keywords
• generate_media.py docstring: Update backend_type list and Supported Backends

6. Tests

• Backend registration tests (API keys, default models, priority order)
• Auto-selection tests (with only this backend's key, with multiple keys)
• SDK call verification (correct params passed through)
• Output file written correctly
• Continuation flow (if applicable)
• Error handling (missing key, API errors)
• Parameter mapping (aspect_ratio, size, duration)
• Update existing tests that assert priority list length/contents

Continuation Store Patterns

Each backend that supports iterative editing needs a continuation mechanism:

Store Pattern Template

class _NewBackendStore:
    def __init__(self, max_items: int = 50):
        self._store: OrderedDict[str, Any] = OrderedDict()
        self._max = max_items

    def save(self, data: Any) -> str:
        store_id = f"prefix_{uuid.uuid4().hex[:12]}"
        if len(self._store) >= self._max:
            self._store.popitem(last=False)  # LRU eviction
        self._store[store_id] = data
        return store_id

    def get(self, store_id: str) -> Any | None:
        return self._store.get(store_id)

_store = _NewBackendStore()

Common Pitfalls

1. Missing from priority list — Backend works when explicitly specified but never auto-selected
2. Sync vs async — Some SDKs are sync-only; wrap in asyncio.to_thread() if needed
3. Ephemeral URLs — Some APIs return temporary URLs; always prefer base64 or download immediately
4. Falsy duration — duration or default treats 0 as falsy; use if duration is not None
5. Existing test breakage — Adding to priority list changes auto-selection; update existing tests that clear env vars
6. Image-to-image gating — The _generate_single_with_input_images function has a backend allowlist

Reference Files