Added a configurable Opus bitrate for audio transcription (#981)

Co-authored-by: Thorsten Sommer <SommerEngineering@users.noreply.github.com>

app/MindWork AI Studio/Settings/DataModel/DataApp.cs

@@ -112,6 +112,18 @@ public sealed class DataApp(Expression<Func<Data, DataApp>>? configSelection = n
     /// </summary>
     public string UseTranscriptionProvider { get; set; } = ManagedConfiguration.Register(configSelection, n => n.UseTranscriptionProvider, string.Empty);
 
+    /// <summary>
+    /// The Opus bitrate used when normalizing uploaded audio/video for transcription.
+    /// </summary>
+    /// <remarks>
+    /// Every recording is re-encoded to mono Opus before it goes to the transcription provider. That
+    /// encoding used to be fixed at 32 kbps, which cost the transcription models entire quiet passages:
+    /// a greeting spoken softly at the start of a recording was simply missing from the transcript. The
+    /// same recording compared at 64 and 128 kbps came back complete, which is why 128 kbps is the
+    /// default here. Users trading accuracy for a smaller upload can still pick a lower bitrate.
+    /// </remarks>
+    public TranscriptionOpusBitrate OpusBitrate { get; set; } = ManagedConfiguration.Register(configSelection, n => n.OpusBitrate, TranscriptionOpusBitrate.KBPS_128);
+
     /// <summary>
     /// The global keyboard shortcut for toggling voice recording.
     /// Uses Tauri's shortcut format, e.g., "CmdOrControl+1" (Cmd+1 on macOS, Ctrl+1 on Windows/Linux).

app/MindWork AI Studio/Settings/DataModel/TranscriptionOpusBitrate.cs

@@ -0,0 +1,14 @@
+namespace AIStudio.Settings.DataModel;
+
+public enum TranscriptionOpusBitrate
+{
+    // The recommended bitrate is deliberately the member with the underlying value 0: when the
+    // settings file holds a value TolerantEnumConverter cannot read, it falls back to that member.
+    // Landing on the lowest bitrate there would silently reintroduce the very defect this setting
+    // exists to prevent -- transcripts losing what was said quietly.
+    KBPS_128 = 0,
+
+    KBPS_32,
+    KBPS_64,
+    KBPS_256,
+}

app/MindWork AI Studio/Settings/DataModel/TranscriptionOpusBitrateExtensions.cs

@@ -0,0 +1,29 @@
+using AIStudio.Tools.PluginSystem;
+
+namespace AIStudio.Settings.DataModel;
+
+public static class TranscriptionOpusBitrateExtensions
+{
+    private static string TB(string fallbackEN) => I18N.I.T(fallbackEN, typeof(TranscriptionOpusBitrateExtensions).Namespace, nameof(TranscriptionOpusBitrateExtensions));
+
+    public static string GetName(this TranscriptionOpusBitrate bitrate) => bitrate switch
+    {
+        TranscriptionOpusBitrate.KBPS_32 => TB("32 kbps (smallest upload, lowest accuracy)"),
+        TranscriptionOpusBitrate.KBPS_64 => TB("64 kbps"),
+        TranscriptionOpusBitrate.KBPS_128 => TB("128 kbps (recommended)"),
+        TranscriptionOpusBitrate.KBPS_256 => TB("256 kbps (largest upload, highest accuracy)"),
+        _ => TB("Unknown"),
+    };
+
+    public static uint GetBitsPerSecond(this TranscriptionOpusBitrate bitrate) => bitrate switch
+    {
+        TranscriptionOpusBitrate.KBPS_32 => 32_000,
+        TranscriptionOpusBitrate.KBPS_64 => 64_000,
+        TranscriptionOpusBitrate.KBPS_128 => 128_000,
+        TranscriptionOpusBitrate.KBPS_256 => 256_000,
+
+        // A value we do not know must never mean the lowest quality: that is how quiet passages
+        // went missing from transcripts in the first place. Fall back to the recommended bitrate.
+        _ => 128_000,
+    };
+}