optimize qsv h264 stream startup (#2835)

ErsatzTV.Application/Streaming/HlsSessionWorker.cs

@@ -313,9 +313,6 @@ public class HlsSessionWorker : IHlsSessionWorker
         var sw = Stopwatch.StartNew();
         try
         {
-            DateTimeOffset start = DateTimeOffset.Now;
-            DateTimeOffset finish = start.AddSeconds(8);
-
             string playlistFileName = Path.Combine(_workingDirectory, "live.m3u8");
 
             _logger.LogDebug("Waiting for playlist to exist");
@@ -326,6 +323,10 @@ public class HlsSessionWorker : IHlsSessionWorker
 
             _logger.LogDebug("Playlist exists");
 
+            // start the segment-wait deadline only after the playlist file appears,
+            // so slow pipeline setup (e.g. h264 profile probing) doesn't consume the budget
+            DateTimeOffset finish = DateTimeOffset.Now.AddSeconds(8);
+
             var segmentCount = 0;
             int lastSegmentCount = -1;
             while (DateTimeOffset.Now < finish && segmentCount < initialSegmentCount)

ErsatzTV.Infrastructure/Metadata/LocalStatisticsProvider.cs

@@ -359,9 +359,11 @@ public partial class LocalStatisticsProvider : ILocalStatisticsProvider
         string filePath,
         CancellationToken cancellationToken)
     {
+        // only scans first 30 seconds
         string[] arguments =
         [
             "-hide_banner",
+            "-t", "30",
             "-i", filePath,
             "-c", "copy",
             "-bsf:v", "trace_headers",
@@ -370,6 +372,11 @@ public partial class LocalStatisticsProvider : ILocalStatisticsProvider
 
         var uniqueProfiles = new System.Collections.Generic.HashSet<string>();
 
+        // cancel as soon as we find a second distinct profile_idc
+        using var linkedCts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
+
+        try
+        {
             CommandResult traceHeaders = await Cli.Wrap(ffmpegPath)
                 .WithArguments(arguments)
                 .WithValidation(CommandResultValidation.None)
@@ -380,9 +387,13 @@ public partial class LocalStatisticsProvider : ILocalStatisticsProvider
                         if (idx >= 0)
                         {
                             uniqueProfiles.Add(line[idx..]);
+                            if (uniqueProfiles.Count > 1)
+                            {
+                                linkedCts.Cancel();
+                            }
                         }
                     }))
-            .ExecuteAsync(cancellationToken);
+                .ExecuteAsync(linkedCts.Token);
 
             if (traceHeaders.ExitCode != 0)
             {
@@ -393,6 +404,11 @@ public partial class LocalStatisticsProvider : ILocalStatisticsProvider
 
                 return Option<int>.None;
             }
+        }
+        catch (OperationCanceledException) when (!cancellationToken.IsCancellationRequested)
+        {
+            // nothing to do here - canceled because a second profile was found
+        }
 
         return uniqueProfiles.Count;
     }