.Net: Improved Audio API by adding default setting values (#5026)

### Motivation and Context

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Current audio interfaces have optional execution settings parameters in
order to be able to use audio API through Kernel in the future, where
execution settings are optional. But when using audio services directly,
this is not user friendly, because when optional execution settings are
not configured, services will throw an error.

In case of text-to-audio service, required field is voice. This PR sets
default value to `alloy` with the ability to overwrite.
For audio-to-text service, required field is filename. This PR sets
default value to `file.mp3` with the ability to overwrite.

With these changes execution settings are no longer required (they are
optional) for text-to-audio and audio-to-text conversion.

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

dotnet/src/Connectors/Connectors.OpenAI/AudioToText/OpenAIAudioToTextExecutionSettings.cs

@@ -2,6 +2,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Text.Json;
 using System.Text.Json.Serialization;
 using Microsoft.SemanticKernel.Text;
@@ -11,6 +12,7 @@ namespace Microsoft.SemanticKernel.Connectors.OpenAI;
 /// <summary>
 /// Execution settings for OpenAI audio-to-text request.
 /// </summary>
+[Experimental("SKEXP0005")]
 public sealed class OpenAIAudioToTextExecutionSettings : PromptExecutionSettings
 {
     /// <summary>
@@ -92,6 +94,14 @@ public float Temperature
         }
     }
 
+    /// <summary>
+    /// Creates an instance of <see cref="OpenAIAudioToTextExecutionSettings"/> class with default filename - "file.mp3".
+    /// </summary>
+    public OpenAIAudioToTextExecutionSettings()
+        : this(DefaultFilename)
+    {
+    }
+
     /// <summary>
     /// Creates an instance of <see cref="OpenAIAudioToTextExecutionSettings"/> class.
     /// </summary>
@@ -124,7 +134,7 @@ public override PromptExecutionSettings Clone()
     {
         if (executionSettings is null)
         {
-            return null;
+            return new OpenAIAudioToTextExecutionSettings();
         }
 
         if (executionSettings is OpenAIAudioToTextExecutionSettings settings)
@@ -146,6 +156,8 @@ public override PromptExecutionSettings Clone()
 
     #region private ================================================================================
 
+    private const string DefaultFilename = "file.mp3";
+
     private float _temperature = 0;
     private string _responseFormat = "json";
     private string _filename;

dotnet/src/Connectors/Connectors.OpenAI/TextToAudio/OpenAITextToAudioExecutionSettings.cs

@@ -2,6 +2,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Text.Json;
 using System.Text.Json.Serialization;
 using Microsoft.SemanticKernel.Text;
@@ -11,6 +12,7 @@ namespace Microsoft.SemanticKernel.Connectors.OpenAI;
 /// <summary>
 /// Execution settings for OpenAI text-to-audio request.
 /// </summary>
+[Experimental("SKEXP0005")]
 public sealed class OpenAITextToAudioExecutionSettings : PromptExecutionSettings
 {
     /// <summary>
@@ -58,6 +60,14 @@ public float Speed
         }
     }
 
+    /// <summary>
+    /// Creates an instance of <see cref="OpenAITextToAudioExecutionSettings"/> class with default voice - "alloy".
+    /// </summary>
+    public OpenAITextToAudioExecutionSettings()
+        : this(DefaultVoice)
+    {
+    }
+
     /// <summary>
     /// Creates an instance of <see cref="OpenAITextToAudioExecutionSettings"/> class.
     /// </summary>
@@ -88,7 +98,7 @@ public override PromptExecutionSettings Clone()
     {
         if (executionSettings is null)
         {
-            return null;
+            return new OpenAITextToAudioExecutionSettings();
         }
 
         if (executionSettings is OpenAITextToAudioExecutionSettings settings)
@@ -110,6 +120,8 @@ public override PromptExecutionSettings Clone()
 
     #region private ================================================================================
 
+    private const string DefaultVoice = "alloy";
+
     private float _speed = 1.0f;
     private string _responseFormat = "mp3";
     private string _voice;

dotnet/src/Connectors/Connectors.UnitTests/OpenAI/AudioToText/AzureOpenAIAudioToTextServiceTests.cs

@@ -121,7 +121,6 @@ public void Dispose()
 
     public static TheoryData<OpenAIAudioToTextExecutionSettings?, Type> ExecutionSettings => new()
     {
-        { null, typeof(ArgumentNullException) },
         { new OpenAIAudioToTextExecutionSettings(""), typeof(ArgumentException) },
         { new OpenAIAudioToTextExecutionSettings("file"), typeof(ArgumentException) }
     };

dotnet/src/Connectors/Connectors.UnitTests/OpenAI/AudioToText/OpenAIAudioToTextExecutionSettingsTests.cs

@@ -13,9 +13,9 @@ namespace SemanticKernel.Connectors.UnitTests.OpenAI.AudioToText;
 public sealed class OpenAIAudioToTextExecutionSettingsTests
 {
     [Fact]
-    public void ItReturnsNullWhenSettingsAreNull()
+    public void ItReturnsDefaultSettingsWhenSettingsAreNull()
     {
-        Assert.Null(OpenAIAudioToTextExecutionSettings.FromExecutionSettings(null));
+        Assert.NotNull(OpenAIAudioToTextExecutionSettings.FromExecutionSettings(null));
     }
 
     [Fact]

dotnet/src/Connectors/Connectors.UnitTests/OpenAI/TextToAudio/AzureOpenAITextToAudioServiceTests.cs

@@ -124,7 +124,6 @@ public void Dispose()
 
     public static TheoryData<OpenAITextToAudioExecutionSettings?, Type> ExecutionSettings => new()
     {
-        { null, typeof(ArgumentNullException) },
         { new OpenAITextToAudioExecutionSettings(""), typeof(ArgumentException) },
     };
 }

dotnet/src/Connectors/Connectors.UnitTests/OpenAI/TextToAudio/OpenAITextToAudioExecutionSettingsTests.cs

@@ -13,9 +13,9 @@ namespace SemanticKernel.Connectors.UnitTests.OpenAI.TextToAudio;
 public sealed class OpenAITextToAudioExecutionSettingsTests
 {
     [Fact]
-    public void ItReturnsNullWhenSettingsAreNull()
+    public void ItReturnsDefaultSettingsWhenSettingsAreNull()
     {
-        Assert.Null(OpenAITextToAudioExecutionSettings.FromExecutionSettings(null));
+        Assert.NotNull(OpenAITextToAudioExecutionSettings.FromExecutionSettings(null));
     }
 
     [Fact]

dotnet/src/Connectors/Connectors.UnitTests/OpenAI/TextToAudio/OpenAITextToAudioServiceTests.cs

@@ -123,7 +123,6 @@ public void Dispose()
 
     public static TheoryData<OpenAITextToAudioExecutionSettings?, Type> ExecutionSettings => new()
     {
-        { null, typeof(ArgumentNullException) },
         { new OpenAITextToAudioExecutionSettings(""), typeof(ArgumentException) },
     };
 }

dotnet/src/IntegrationTests/Connectors/OpenAI/OpenAITextToAudioTests.cs

@@ -39,7 +39,7 @@ public async Task OpenAITextToAudioTestAsync()
         var service = new OpenAITextToAudioService(openAIConfiguration.ModelId, openAIConfiguration.ApiKey);
 
         // Act
-        var result = await service.GetAudioContentAsync("The sun rises in the east and sets in the west.", new OpenAITextToAudioExecutionSettings("alloy"));
+        var result = await service.GetAudioContentAsync("The sun rises in the east and sets in the west.");
 
         // Assert
         Assert.NotNull(result?.Data);
@@ -59,7 +59,7 @@ public async Task AzureOpenAITextToAudioTestAsync()
             azureOpenAIConfiguration.ApiKey);
 
         // Act
-        var result = await service.GetAudioContentAsync("The sun rises in the east and sets in the west.", new OpenAITextToAudioExecutionSettings("alloy"));
+        var result = await service.GetAudioContentAsync("The sun rises in the east and sets in the west.");
 
         // Assert
         Assert.NotNull(result?.Data);