Overhaul HLS streaming (#3274)

* Overhaul HLS streaming
* Fix streaming transcode ffmpeg zombie processes
* Add changelog and release notes
* Documentation
---------
Co-authored-by: WithoutPants <53250216+WithoutPants@users.noreply.github.com>

internal/manager/manager.go

@@ -108,8 +108,9 @@ type Manager struct {
 
 	Paths *paths.Paths
 
-	FFMPEG  ffmpeg.FFMpeg
-	FFProbe ffmpeg.FFProbe
+	FFMPEG        ffmpeg.FFMpeg
+	FFProbe       ffmpeg.FFProbe
+	StreamManager *ffmpeg.StreamManager
 
 	ReadLockManager *fsutil.ReadLockManager
 
@@ -430,6 +431,7 @@ func initFFMPEG(ctx context.Context) error {
 
 		instance.FFMPEG = ffmpeg.FFMpeg(ffmpegPath)
 		instance.FFProbe = ffmpeg.FFProbe(ffprobePath)
+		instance.RefreshStreamManager()
 	}
 
 	return nil
@@ -564,6 +566,19 @@ func (s *Manager) RefreshScraperCache() {
 	s.ScraperCache = s.initScraperCache()
 }
 
+// RefreshStreamManager refreshes the stream manager. Call this when cache directory
+// changes.
+func (s *Manager) RefreshStreamManager() {
+	// shutdown existing manager if needed
+	if s.StreamManager != nil {
+		s.StreamManager.Shutdown()
+		s.StreamManager = nil
+	}
+
+	cacheDir := s.Config.GetCachePath()
+	s.StreamManager = ffmpeg.NewStreamManager(cacheDir, s.FFMPEG, s.FFProbe, s.Config, s.ReadLockManager)
+}
+
 func setSetupDefaults(input *SetupInput) {
 	if input.ConfigLocation == "" {
 		input.ConfigLocation = filepath.Join(fsutil.GetHomeDirectory(), ".stash", "config.yml")
@@ -735,6 +750,11 @@ func (s *Manager) Shutdown(code int) {
 	// stop any profiling at exit
 	pprof.StopCPUProfile()
 
+	if s.StreamManager != nil {
+		s.StreamManager.Shutdown()
+		s.StreamManager = nil
+	}
+
 	// TODO: Each part of the manager needs to gracefully stop at some point
 	// for now, we just close the database.
 	err := s.Database.Close()