Add audio related endpoint docs for AI server.

Author: Layoric

MyApp/_pages/ai-server/usage/audio-endpoints.md

@@ -0,0 +1,46 @@
+---
+title: "Transcribing Audio"
+---
+
+# Transcribing Audio
+
+AI Server can transcribe audio files to text using the Speech-to-Text provider. This is powered by the Whisper model and is hosted on your own ComfyUI Agent.
+
+## Using Speech-to-Text
+
+To transcribe an audio file to text, you can use the `SpeechToText` request:
+
+```csharp
+var request = new SpeechToText{};
+
+var response = await client.PostFilesWithRequest<GenerationResponse>(
+    request,
+    [new UploadFile("audio", File.OpenRead("audio.wav"), "audio.wav")]
+);
+
+// Two texts are returned
+// The first is the timestamped text json with `start` and `end` timestamps
+var textWithTimestamps = response.TextOutputs[0].Text;
+// The second is the plain text
+var textOnly = response.TextOutputs[1].Text;
+```
+
+## Text To Speech
+
+AI Server also has a Text-to-Speech endpoint that works with the ComfyUI Agent. This can be used to generate audio files from text.
+
+```csharp
+var request = new TextToSpeech
+{
+    Text = "Hello, how are you?",
+    Sync = true
+};
+
+var response = await client.PostAsync(request);
+response.Outputs[0].Url.DownloadFileTo("hello.mp3");
+```
+
+The ComfyUI Agent uses PiperTTS to generate the audio files. You can configure download the necessary models by setting the `DEFAULT_MODELS` in the `.env` file to include `text-to-speech` for your ComfyUI Agent.
+If you have included an `OPENAI_API_KEY` in your `.env` file, you can also use the OpenAI API to generate audio files from text. By default, this uses their 'tts-1:alloy' model, while PiperTTS via ComfyUI Agent uses the preconfigured 'high:en_US-lessac' model.
+
+See the [`/lib/data/ai-models.json`](/lib/data/ai-models.json) file for more information on the available models.