reduce initial hls segmenter delay (#406)

CHANGELOG.md

@@ -4,6 +4,8 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ## [Unreleased]
+### Changed
+- Reduce initial `HLS Segmenter` delay from 5 seconds to 3 seconds
 
 ## [0.1.0-alpha] - 2021-10-08
 ### Added

ErsatzTV.Application/Streaming/Commands/StartFFmpegSessionHandler.cs

@@ -5,6 +5,7 @@ using System.Threading.Channels;
 using System.Threading.Tasks;
 using ErsatzTV.Core;
 using ErsatzTV.Core.Errors;
+using ErsatzTV.Core.FFmpeg;
 using ErsatzTV.Core.Interfaces.FFmpeg;
 using ErsatzTV.Core.Interfaces.Metadata;
 using LanguageExt;
@@ -45,7 +46,7 @@ namespace ErsatzTV.Application.Streaming.Commands
             await _channel.WriteAsync(request);
 
             // TODO: find some other way to let ffmpeg get ahead
-            await Task.Delay(TimeSpan.FromSeconds(5));
+            await Task.Delay(FFmpegSegmenterService.SegmenterDelay);
 
             return Unit.Default;
         }

ErsatzTV.Application/Streaming/Queries/GetPlayoutItemProcessByChannelNumberHandler.cs

@@ -54,7 +54,12 @@ namespace ErsatzTV.Application.Streaming.Queries
             Channel channel,
             string ffmpegPath)
         {
-            DateTimeOffset now = DateTimeOffset.Now;
+            DateTimeOffset now = request.Mode switch
+            {
+                "segmenter" => DateTimeOffset.Now + FFmpegSegmenterService.SegmenterDelay,
+                _ => DateTimeOffset.Now
+            };
+            
             Either<BaseError, PlayoutItemWithPath> maybePlayoutItem = await dbContext.PlayoutItems
                 .Include(i => i.MediaItem)
                 .ThenInclude(mi => (mi as Episode).MediaVersions)
@@ -113,7 +118,8 @@ namespace ErsatzTV.Application.Streaming.Queries
                             playoutItemWithPath.PlayoutItem.StartOffset,
                             request.StartAtZero ? playoutItemWithPath.PlayoutItem.StartOffset : now,
                             maybeGlobalWatermark,
-                            maybeVaapiDriver));
+                            maybeVaapiDriver,
+                            request.StartAtZero));
                 },
                 async error =>
                 {

ErsatzTV.Core.Tests/FFmpeg/TranscodingTests.cs

@@ -184,7 +184,8 @@ namespace ErsatzTV.Core.Tests.FFmpeg
                 now,
                 now,
                 None,
-                None);
+                None,
+                false);
 
             process.StartInfo.RedirectStandardError = true;
 

ErsatzTV.Core/FFmpeg/FFmpegProcessBuilder.cs

@@ -310,8 +310,11 @@ namespace ErsatzTV.Core.FFmpeg
             return this;
         }
 
-        public FFmpegProcessBuilder WithHls(string channelNumber, MediaVersion mediaVersion)
+        public FFmpegProcessBuilder WithHls(string channelNumber, MediaVersion mediaVersion, bool startAtZero)
         {
+            const int INITIAL_SEGMENT_SECONDS = 1;
+            const int SUBSEQUENT_SEGMENT_SECONDS = 2;
+            
             if (!int.TryParse(mediaVersion.RFrameRate, out int frameRate))
             {
                 string[] split = (mediaVersion.RFrameRate ?? string.Empty).Split("/");
@@ -326,15 +329,17 @@ namespace ErsatzTV.Core.FFmpeg
                 }
             }
 
+            int segmentSeconds = startAtZero ? SUBSEQUENT_SEGMENT_SECONDS : INITIAL_SEGMENT_SECONDS;
+            
             _arguments.AddRange(
                 new[]
                 {
-                    "-g", $"{frameRate * 2}",
-                    "-keyint_min", $"{frameRate * 2}",
-                    // "-force_key_frames",
-                    // "expr:gte(t,n_forced*2)",
+                    "-use_wallclock_as_timestamps", "1",
+                    "-g", $"{frameRate * segmentSeconds}",
+                    "-keyint_min", $"{frameRate * segmentSeconds}",
+                    "-force_key_frames", $"expr:gte(t,n_forced*{segmentSeconds})",
                     "-f", "hls",
-                    "-hls_time", "2",
+                    "-hls_time", $"{segmentSeconds}",
                     "-hls_list_size", "10",
                     "-segment_list_flags", "+live",
                     "-hls_flags", "delete_segments+program_date_time+append_list+discont_start+omit_endlist",

ErsatzTV.Core/FFmpeg/FFmpegProcessService.cs

@@ -39,7 +39,8 @@ namespace ErsatzTV.Core.FFmpeg
             DateTimeOffset start,
             DateTimeOffset now,
             Option<ChannelWatermark> globalWatermark,
-            Option<VaapiDriver> maybeVaapiDriver)
+            Option<VaapiDriver> maybeVaapiDriver,
+            bool startAtZero)
         {
             MediaStream videoStream = await _ffmpegStreamSelector.SelectVideoStream(channel, version);
             Option<MediaStream> maybeAudioStream = await _ffmpegStreamSelector.SelectAudioStream(channel, version);
@@ -118,7 +119,7 @@ namespace ErsatzTV.Core.FFmpeg
             {
                 // HLS needs to segment and generate playlist
                 case StreamingMode.HttpLiveStreamingSegmenter:
-                    return builder.WithHls(channel.Number, version)
+                    return builder.WithHls(channel.Number, version, startAtZero)
                         .Build();
                 default:
                     return builder.WithFormat("mpegts")

ErsatzTV.Core/FFmpeg/FFmpegSegmenterService.cs

@@ -12,6 +12,8 @@ namespace ErsatzTV.Core.FFmpeg
 {
     public class FFmpegSegmenterService : IFFmpegSegmenterService
     {
+        public static readonly TimeSpan SegmenterDelay = TimeSpan.FromSeconds(3);
+        
         private static readonly ConcurrentDictionary<string, ProcessAndToken> Processes = new();
 
         private readonly ILogger<FFmpegSegmenterService> _logger;