lower gop size and keyframe interval

CHANGELOG.md

@@ -25,6 +25,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Move dark/light mode toggle to **Settings** > **UI**
 - Use latest (non-deprecated) authorization method with Jellyfin API
 - Replace direct Discord links with new contact page https://ersatztv.org/contact which also includes other options like Matrix
+- Lower GOP size and keyframe interval from four seconds to two seconds in accordance with HLS2 draft spec recommendations
 
 ### Fixed
 - Improve stability of playback orders `Shuffle` and `Shuffle in Order` over time

ErsatzTV.FFmpeg/OutputFormat/OutputFormatConcatHls.cs

@@ -32,8 +32,8 @@ public class OutputFormatConcatHls : IPipelineStep
 
             return
             [
-                "-g", $"{OutputFormatHls.SegmentSeconds}/2",
+                "-g", $"{OutputFormatHls.KeyframeIntervalSeconds}",
-                "-force_key_frames", $"expr:gte(t,n_forced*{OutputFormatHls.SegmentSeconds}/2)",
+                "-force_key_frames", $"expr:gte(t,n_forced*{OutputFormatHls.KeyframeIntervalSeconds})",
                 "-f", "hls",
                 "-hls_segment_type", segmentType,
                 //"-hls_init_time", "2",

ErsatzTV.FFmpeg/OutputFormat/OutputFormatHls.cs

@@ -6,6 +6,7 @@ namespace ErsatzTV.FFmpeg.OutputFormat;
 public class OutputFormatHls : IPipelineStep
 {
     public const int SegmentSeconds = 4;
+    public const int KeyframeIntervalSeconds = 2;
 
     private readonly FrameState _desiredState;
     private readonly bool _isFirstTranscode;
@@ -55,7 +56,7 @@ public class OutputFormatHls : IPipelineStep
 
             int gop = _oneSecondGop
                 ? (int)Math.Round(frameRate.ParsedFrameRate)
-                : (int)Math.Round(frameRate.ParsedFrameRate * SegmentSeconds);
+                : (int)Math.Round(frameRate.ParsedFrameRate * KeyframeIntervalSeconds);
 
             List<string> result = [];
 
@@ -64,8 +65,8 @@ public class OutputFormatHls : IPipelineStep
                 result.AddRange(
                 [
                     "-g", $"{gop}",
-                    "-keyint_min", $"{(int)Math.Round(frameRate.ParsedFrameRate * SegmentSeconds)}",
+                    "-keyint_min", $"{(int)Math.Round(frameRate.ParsedFrameRate * KeyframeIntervalSeconds)}",
-                    "-force_key_frames", $"expr:gte(t,n_forced*{SegmentSeconds})"
+                    "-force_key_frames", $"expr:gte(t,n_forced*{KeyframeIntervalSeconds})"
                 ]);
             }
 

ErsatzTV/Pages/FFmpegEditor.razor

@@ -282,7 +282,14 @@
                 <div class="d-flex">
                     <MudText>Format</MudText>
                 </div>
-                <MudSelect @bind-Value="_model.AudioFormat" For="@(() => _model.AudioFormat)">
+                @{
+                    string helperText = string.Empty;
+                    if (_model.AudioFormat is FFmpegProfileAudioFormat.AacLatm)
+                    {
+                        helperText = "aac (latm) is ONLY intended for DVB-C; anything else should use aac instead which uses ADTS";
+                    }
+                }
+                <MudSelect @bind-Value="_model.AudioFormat" For="@(() => _model.AudioFormat)" HelperText="@helperText">
                     <MudSelectItem Value="@FFmpegProfileAudioFormat.Aac">aac</MudSelectItem>
                     <MudSelectItem Value="@FFmpegProfileAudioFormat.Ac3">ac3</MudSelectItem>
                     <MudSelectItem Value="@FFmpegProfileAudioFormat.AacLatm">aac (latm)</MudSelectItem>