Add audio vbr calculation

Jellyfin.Api/Controllers/DynamicHlsController.cs

@@ -1685,14 +1685,25 @@ public class DynamicHlsController : BaseJellyfinApiController
 
             audioTranscodeParams += "-acodec " + audioCodec;
 
-            if (state.OutputAudioBitrate.HasValue)
+            var audioBitrate = state.OutputAudioBitrate;
+            var audioChannels = state.OutputAudioChannels;
+
+            if (audioBitrate.HasValue)
             {
-                audioTranscodeParams += " -ab " + state.OutputAudioBitrate.Value.ToString(CultureInfo.InvariantCulture);
+                string vbrParam;
+                if (_encodingOptions.EnableAudioVbr && (vbrParam = _encodingHelper.GetAudioVbrModeParam(state.OutputAudioCodec, audioBitrate.Value / audioChannels ?? 2)) != null)
+                {
+                    audioTranscodeParams += vbrParam;
+                }
+                else
+                {
+                    audioTranscodeParams += " -ab " + audioBitrate.Value.ToString(CultureInfo.InvariantCulture);
+                }
             }
 
-            if (state.OutputAudioChannels.HasValue)
+            if (audioChannels.HasValue)
             {
-                audioTranscodeParams += " -ac " + state.OutputAudioChannels.Value.ToString(CultureInfo.InvariantCulture);
+                audioTranscodeParams += " -ac " + audioChannels.Value.ToString(CultureInfo.InvariantCulture);
             }
 
             if (state.OutputAudioSampleRate.HasValue)
@@ -1747,7 +1758,15 @@ public class DynamicHlsController : BaseJellyfinApiController
 
         if (bitrate.HasValue)
         {
-            args += " -ab " + bitrate.Value.ToString(CultureInfo.InvariantCulture);
+            string vbrParam;
+            if (_encodingOptions.EnableAudioVbr && (vbrParam = _encodingHelper.GetAudioVbrModeParam(state.OutputAudioCodec, bitrate.Value / channels ?? 2)) != null)
+            {
+                args += vbrParam;
+            }
+            else
+            {
+                args += " -ab " + bitrate.Value.ToString(CultureInfo.InvariantCulture);
+            }
         }
 
         if (state.OutputAudioSampleRate.HasValue)

MediaBrowser.Controller/MediaEncoding/EncodingHelper.cs

@@ -2160,6 +2160,47 @@ namespace MediaBrowser.Controller.MediaEncoding
             return 128000;
         }
 
+        public string GetAudioVbrModeParam(string encoder, int bitratePerChannel)
+        {
+            if (encoder == "libfdk_aac")
+            {
+                return " -vbr:a " + bitratePerChannel switch
+                {
+                    < 32000 => "1",
+                    < 48000 => "2",
+                    < 64000 => "3",
+                    < 96000 => "4",
+                    _ => "5"
+                };
+            }
+
+            if (encoder == "libmp3lame")
+            {
+                return " -qscale:a " + bitratePerChannel switch
+                {
+                    < 48000 => "8",
+                    < 64000 => "6",
+                    < 88000 => "4",
+                    < 112000 => "2",
+                    _ => "0"
+                };
+            }
+
+            if (encoder == "libvorbis")
+            {
+                return " -qscale:a " + bitratePerChannel switch
+                {
+                    < 40000 => "0",
+                    < 56000 => "2",
+                    < 80000 => "4",
+                    < 112000 => "6",
+                    _ => "8"
+                };
+            }
+
+            return null;
+        }
+
         public string GetAudioFilterParam(EncodingJobInfo state, EncodingOptions encodingOptions)
         {
             var channels = state.OutputAudioChannels;
@@ -5801,7 +5842,15 @@ namespace MediaBrowser.Controller.MediaEncoding
 
             if (bitrate.HasValue)
             {
-                args += " -ab " + bitrate.Value.ToString(CultureInfo.InvariantCulture);
+                string vbrParam;
+                if (encodingOptions.EnableAudioVbr && (vbrParam = GetAudioVbrModeParam(codec, bitrate.Value / channels ?? 2)) != null)
+                {
+                    args += vbrParam;
+                }
+                else
+                {
+                    args += " -ab " + bitrate.Value.ToString(CultureInfo.InvariantCulture);
+                }
             }
 
             if (state.OutputAudioSampleRate.HasValue)
@@ -5819,13 +5868,22 @@ namespace MediaBrowser.Controller.MediaEncoding
             var audioTranscodeParams = new List<string>();
 
             var bitrate = state.OutputAudioBitrate;
+            var channels = state.OutputAudioChannels;
 
             if (bitrate.HasValue)
             {
-                audioTranscodeParams.Add("-ab " + bitrate.Value.ToString(CultureInfo.InvariantCulture));
+                string vbrParam;
+                if (encodingOptions.EnableAudioVbr && (vbrParam = GetAudioVbrModeParam(state.OutputAudioCodec, bitrate.Value / channels ?? 2)) != null)
+                {
+                    audioTranscodeParams.Add(vbrParam);
+                }
+                else
+                {
+                    audioTranscodeParams.Add("-ab " + bitrate.Value.ToString(CultureInfo.InvariantCulture));
+                }
             }
 
-            if (state.OutputAudioChannels.HasValue)
+            if (channels.HasValue)
             {
                 audioTranscodeParams.Add("-ac " + state.OutputAudioChannels.Value.ToString(CultureInfo.InvariantCulture));
             }

MediaBrowser.Model/Configuration/EncodingOptions.cs

@@ -14,6 +14,7 @@ public class EncodingOptions
     public EncodingOptions()
     {
         EnableFallbackFont = false;
+        EnableAudioVbr = false;
         DownMixAudioBoost = 2;
         DownMixStereoAlgorithm = DownMixStereoAlgorithms.None;
         MaxMuxingQueueSize = 2048;
@@ -70,6 +71,11 @@ public class EncodingOptions
     /// </summary>
     public bool EnableFallbackFont { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether audio VBR is enabled.
+    /// </summary>
+    public bool EnableAudioVbr { get; set; }
+
     /// <summary>
     /// Gets or sets the audio boost applied when downmixing audio.
     /// </summary>