fix hls playlist filtering (#2435)

* add failing test

* fix hls playlist filtering

CHANGELOG.md

@@ -46,6 +46,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Fix playback of Jellyfin content with unknown color range
 - Block schedules: skip collections (block items) that will never fit in block duration
 - Block schedules: skip media items that will never fit in block duration
+- Fix HLS playlist generation for clients that actually care about discontinuities (like hls.js)
+  - This should resolve most playback issues with built-in channel preview
 
 ## [25.6.0] - 2025-09-14
 ### Added

ErsatzTV.Core.Tests/FFmpeg/HlsPlaylistFilterTests.cs

@@ -551,6 +551,54 @@ live000065.ts
 "));
     }
 
+    [Test]
+    public void HlsPlaylistFilter_ShouldHandleDiscontinuitySequenceOnSegmentRemoval()
+    {
+        var start = new DateTimeOffset(2025, 9, 17, 10, 11, 5, 31, TimeSpan.FromHours(-5));
+        string[] input = NormalizeLineEndings(
+            @"#EXTM3U
+#EXT-X-VERSION:6
+#EXT-X-TARGETDURATION:4
+#EXT-X-MEDIA-SEQUENCE:46
+#EXT-X-DISCONTINUITY-SEQUENCE:2
+#EXT-X-INDEPENDENT-SEGMENTS
+#EXTINF:1.734000,
+#EXT-X-PROGRAM-DATE-TIME:2025-09-17T10:11:05.031-0500
+live000046.ts
+#EXT-X-DISCONTINUITY
+#EXTINF:4.004000,
+#EXT-X-PROGRAM-DATE-TIME:2025-09-17T10:11:06.765-0500
+live000047.ts
+#EXTINF:4.004000,
+#EXT-X-PROGRAM-DATE-TIME:2025-09-17T10:11:10.769-0500
+live000048.ts
+").Split(Environment.NewLine);
+
+        // filter 'live000046.ts'
+        var filterBefore = start.AddSeconds(2);
+
+        TrimPlaylistResult result = _hlsPlaylistFilter.TrimPlaylist(start, filterBefore, input, 2);
+
+        result.Sequence.ShouldBe(47);
+
+        string expectedPlaylist = NormalizeLineEndings(
+            @"#EXTM3U
+#EXT-X-VERSION:6
+#EXT-X-TARGETDURATION:4
+#EXT-X-MEDIA-SEQUENCE:47
+#EXT-X-DISCONTINUITY-SEQUENCE:3
+#EXT-X-INDEPENDENT-SEGMENTS
+#EXTINF:4.004000,
+#EXT-X-PROGRAM-DATE-TIME:2025-09-17T10:11:06.765-0500
+live000047.ts
+#EXTINF:4.004000,
+#EXT-X-PROGRAM-DATE-TIME:2025-09-17T10:11:10.769-0500
+live000048.ts
+");
+
+        result.Playlist.ShouldBe(expectedPlaylist);
+    }
+
     private static string NormalizeLineEndings(string str) =>
         str
             .Replace("\r\n", "\n")

ErsatzTV.Core/FFmpeg/HlsPlaylistFilter.cs

@@ -61,11 +61,11 @@ public class HlsPlaylistFilter : IHlsPlaylistFilter
                     continue;
                 }
 
-                var duration = TimeSpan.FromSeconds(
-                    double.Parse(
-                        lines[i].TrimEnd(',').Split(':')[1],
-                        NumberStyles.Number,
-                        CultureInfo.InvariantCulture));
+                var durationDecimal = decimal.Parse(
+                    lines[i].TrimEnd(',').Split(':')[1],
+                    NumberStyles.Number,
+                    CultureInfo.InvariantCulture);
+                var duration = TimeSpan.FromTicks((long)(durationDecimal * TimeSpan.TicksPerSecond));
 
                 items.Add(new PlaylistSegment(currentTime, lines[i], lines[i + 2]));
 
@@ -168,11 +168,17 @@ public class HlsPlaylistFilter : IHlsPlaylistFilter
             switch (items[i])
             {
                 case PlaylistDiscontinuity:
-                    if (i == items.Count - 1 || allSegments.Contains(items[i + 1]))
+                    if (i < items.Count - 1 && allSegments.Contains(items[i + 1]))
+                    {
+                        if (items[i + 1] is PlaylistSegment nextSegment && allSegments.Head() != nextSegment)
+                        {
+                            output.AppendLine("#EXT-X-DISCONTINUITY");
+                        }
+                    }
+                    else if (i == items.Count - 1 && allSegments.Count > 0) // discontinuity at the end
                     {
                         output.AppendLine("#EXT-X-DISCONTINUITY");
                     }
-
                     break;
                 case PlaylistSegment segment:
                     if (allSegments.Contains(segment))