Support using GenAI for audio transcription (#24396)

* Add support for running transcription with GenAI

* Improve audio joining

* Fix GenAI model capability reporting

* Support language correctly

* Migrate existing users to keep english selected

* Fix models

* Fix tests

* Fix accepted null model

* Handle slwo providers

frigate/genai/__init__.py

@@ -338,6 +338,11 @@ class GenAIClient:
         """Whether the configured model can generate embeddings via embed()."""
         return False
 
+    @property
+    def supports_transcription(self) -> bool:
+        """Whether the configured model can transcribe audio via transcribe()."""
+        return False
+
     def list_models(self) -> list[str]:
         """Return the list of model names available from this provider.
 
@@ -345,6 +350,21 @@ class GenAIClient:
         """
         return []
 
+    def list_model_capabilities(self) -> dict[str, dict[str, bool]]:
+        """Return capability flags for each model the provider serves.
+
+        Only providers whose backend advertises capabilities per model can
+        populate this; llama.cpp reports input modalities for every model it
+        serves, so one request describes them all. An empty mapping means "no
+        per-model information available", and callers fall back to this
+        client's own capability properties, which describe only the configured
+        model. A model absent from a non-empty mapping means the same thing.
+
+        Returns:
+            Model name (including aliases) to its capability flags
+        """
+        return {}
+
     def get_context_size(self) -> int:
         """Get the context window size for this provider in tokens."""
         return 4096
@@ -376,6 +396,33 @@ class GenAIClient:
         )
         return []
 
+    def transcribe(
+        self,
+        audio: bytes,
+        language: str | None = None,
+        mime_type: str = "audio/wav",
+    ) -> str | None:
+        """Transcribe speech audio to text.
+
+        Audio is passed as a self-describing blob rather than raw samples so
+        every provider receives a container it can declare, and WAV framing
+        lives in one place instead of in each plugin.
+
+        Args:
+            audio: The encoded audio payload (WAV bytes by default)
+            language: Optional ISO language hint for the provider
+            mime_type: Media type of ``audio``
+
+        Returns:
+            The transcript, or None when the provider cannot produce one
+        """
+        logger.warning(
+            "%s does not support transcription. "
+            "This method should be overridden by the provider implementation.",
+            self.__class__.__name__,
+        )
+        return None
+
     def chat_with_tools(
         self,
         messages: list[dict[str, Any]],