fix(docs): enhance transcription API documentation

spring-ai-docs/src/main/antora/modules/ROOT/pages/api/audio/transcriptions.adoc

@@ -1,5 +1,107 @@
 [[Transcription]]
 = Transcription API
 
-Spring AI provides support for OpenAI's Transcription API.
-When additional providers for Transcription are implemented, a common `AudioTranscriptionModel` interface will be extracted.
+Spring AI provides a unified API for Speech-to-Text transcription through the `TranscriptionModel` interface. This allows you to write portable code that works across different transcription providers.
+
+== Supported Providers
+
+- xref:api/audio/transcriptions/openai-transcriptions.adoc[OpenAI's Whisper API]
+- xref:api/audio/transcriptions/azure-openai-transcriptions.adoc[Azure OpenAI Whisper API]
+
+== Common Interface
+
+All transcription providers implement the following shared interface:
+
+=== TranscriptionModel
+
+The `TranscriptionModel` interface provides methods for converting audio to text:
+
+[source,java]
+----
+public interface TranscriptionModel extends Model<AudioTranscriptionPrompt, AudioTranscriptionResponse> {
+
+    /**
+     * Transcribes the audio from the given prompt.
+     */
+    AudioTranscriptionResponse call(AudioTranscriptionPrompt transcriptionPrompt);
+
+    /**
+     * A convenience method for transcribing an audio resource.
+     */
+    default String transcribe(Resource resource) {
+        AudioTranscriptionPrompt prompt = new AudioTranscriptionPrompt(resource);
+        return this.call(prompt).getResult().getOutput();
+    }
+
+    /**
+     * A convenience method for transcribing an audio resource with options.
+     */
+    default String transcribe(Resource resource, AudioTranscriptionOptions options) {
+        AudioTranscriptionPrompt prompt = new AudioTranscriptionPrompt(resource, options);
+        return this.call(prompt).getResult().getOutput();
+    }
+}
+----
+
+=== AudioTranscriptionPrompt
+
+The `AudioTranscriptionPrompt` class encapsulates the input audio and options:
+
+[source,java]
+----
+Resource audioFile = new FileSystemResource("/path/to/audio.mp3");
+AudioTranscriptionPrompt prompt = new AudioTranscriptionPrompt(
+    audioFile,
+    options
+);
+----
+
+=== AudioTranscriptionResponse
+
+The `AudioTranscriptionResponse` class contains the transcribed text and metadata:
+
+[source,java]
+----
+AudioTranscriptionResponse response = model.call(prompt);
+String transcribedText = response.getResult().getOutput();
+AudioTranscriptionResponseMetadata metadata = response.getMetadata();
+----
+
+== Writing Provider-Agnostic Code
+
+One of the key benefits of the shared transcription interface is the ability to write code that works with any transcription provider without modification. The actual provider (OpenAI, Azure OpenAI, etc.) is determined by your Spring Boot configuration, allowing you to switch providers without changing application code.
+
+=== Basic Service Example
+
+The shared interface allows you to write code that works with any transcription provider:
+
+[source,java]
+----
+@Service
+public class TranscriptionService {
+
+    private final TranscriptionModel transcriptionModel;
+
+    public TranscriptionService(TranscriptionModel transcriptionModel) {
+        this.transcriptionModel = transcriptionModel;
+    }
+
+    public String transcribeAudio(Resource audioFile) {
+        return transcriptionModel.transcribe(audioFile);
+    }
+
+    public String transcribeWithOptions(Resource audioFile, AudioTranscriptionOptions options) {
+        AudioTranscriptionPrompt prompt = new AudioTranscriptionPrompt(audioFile, options);
+        AudioTranscriptionResponse response = transcriptionModel.call(prompt);
+        return response.getResult().getOutput();
+    }
+}
+----
+
+This service works seamlessly with OpenAI, Azure OpenAI, or any other transcription provider, with the actual implementation determined by your Spring Boot configuration.
+
+== Provider-Specific Features
+
+While the shared interface provides portability, each provider also offers specific features through provider-specific options classes (e.g., `OpenAiAudioTranscriptionOptions`, `AzureOpenAiAudioTranscriptionOptions`). These classes implement the `AudioTranscriptionOptions` interface while adding provider-specific capabilities.
+
+For detailed information about provider-specific features, see the individual provider documentation pages.