Loseless split is back. Very fast now. Using key frames.

splitter-cli/JobProcessor.cs

@@ -79,8 +79,8 @@ public class JobProcessor(ILogger logger) : LoggingBase(logger, 0), IJobProcesso
         }
         else
         {
-            //processorFactory = i => new PassthroughSplitter(i, _logger);
+            processorFactory = i => new PassthroughSplitter(i, _logger);
-            processorFactory = i => new ReencodeSplitter(i, _logger);
+            //processorFactory = i => new ReencodeSplitter(i, _logger);
         }
 
         var segmentsToUse = predefinedSegments;

splitter-cli/PassthroughSplitter.cs

@@ -82,8 +82,15 @@ public sealed class PassthroughSplitter : LoggingBase, ISegmentProcessor
         var start      = job.SegmentStart;
         var length     = job.SegmentLength;
 
+        // Probe next keyframe packet within a 5-second window
+        var nextKey = ProbeNextKeyframePacket(inputFile, start);
+
+        // Adjust by subtracting X.XX seconds
+        const double shiftBack = 0.1;
+        var seekPos = nextKey > shiftBack ? nextKey - shiftBack : 0.0;
+
         var args =
-            $"-ss {start.ToString(CultureInfo.InvariantCulture)} " +
+            $"-ss {seekPos.ToString(CultureInfo.InvariantCulture)} " +
             $"-i \"{inputFile}\" " +
             $"-t {length.ToString(CultureInfo.InvariantCulture)} " +
             $"-c copy {string.Join(" ", job.Job.Passthrough)} " +
@@ -100,4 +107,60 @@ public sealed class PassthroughSplitter : LoggingBase, ISegmentProcessor
 
         return Process.Start(psi) ?? throw new Exception("Failed to start ffmpeg passthrough.");
     }
+
+    public static double ProbeNextKeyframePacket(string inputFile, double segmentStart, double window = 11.0)
+    {
+        var psi = new ProcessStartInfo
+        {
+            FileName = "ffprobe",
+            Arguments =
+            "-select_streams v " +
+            $"-read_intervals \"{(segmentStart-0.1).ToString(CultureInfo.InvariantCulture)}%+{window.ToString(CultureInfo.InvariantCulture)}\" " +
+            "-skip_frame nokey " +
+            "-show_packets " +
+            "-show_entries packet=pts_time,flags " +
+            "-of compact=p=0 " +
+            "-v quiet " +
+            $"\"{inputFile}\"",
+            RedirectStandardOutput = true,
+            UseShellExecute = false,
+            CreateNoWindow = true
+        };
+
+        using var p = Process.Start(psi);
+        var output = p!.StandardOutput.ReadToEnd();
+        p.WaitForExit();
+
+        double best = double.MaxValue;
+
+        foreach (var line in output.Split('\n'))
+        {
+            if (string.IsNullOrWhiteSpace(line))
+                continue;
+
+            // Example line:
+            // pts_time=23.520000|flags=K__
+            var parts = line.Split('|');
+            if (parts.Length < 2)
+                continue;
+
+            var ptsPart = parts[0].Trim();   // pts_time=23.520000
+            var flagsPart = parts[1].Trim(); // flags=K__
+
+            if (!flagsPart.Contains("K"))
+                continue;
+
+            var ptsStr = ptsPart.Replace("pts_time=", "");
+            if (!double.TryParse(ptsStr, NumberStyles.Float, CultureInfo.InvariantCulture, out var pts))
+                continue;
+
+            if ( best == double.MaxValue)
+                best = pts;
+            if (pts > segmentStart)
+                break;
+        }
+
+        return best == double.MaxValue ? segmentStart : best;
+    }
+
 }