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/running_streams.go

@@ -5,10 +5,10 @@ import (
 	"errors"
 	"io"
 	"net/http"
-	"time"
 
 	"github.com/stashapp/stash/internal/manager/config"
 	"github.com/stashapp/stash/internal/static"
+	"github.com/stashapp/stash/pkg/ffmpeg"
 	"github.com/stashapp/stash/pkg/fsutil"
 	"github.com/stashapp/stash/pkg/logger"
 	"github.com/stashapp/stash/pkg/models"
@@ -16,58 +16,6 @@ import (
 	"github.com/stashapp/stash/pkg/utils"
 )
 
-type StreamRequestContext struct {
-	context.Context
-	ResponseWriter http.ResponseWriter
-}
-
-func NewStreamRequestContext(w http.ResponseWriter, r *http.Request) *StreamRequestContext {
-	return &StreamRequestContext{
-		Context:        r.Context(),
-		ResponseWriter: w,
-	}
-}
-
-func (c *StreamRequestContext) Cancel() {
-	hj, ok := (c.ResponseWriter).(http.Hijacker)
-	if !ok {
-		return
-	}
-
-	// hijack and close the connection
-	conn, bw, _ := hj.Hijack()
-	if conn != nil {
-		if bw != nil {
-			// notify end of stream
-			_, err := bw.WriteString("0\r\n")
-			if err != nil {
-				logger.Warnf("unable to write end of stream: %v", err)
-			}
-			_, err = bw.WriteString("\r\n")
-			if err != nil {
-				logger.Warnf("unable to write end of stream: %v", err)
-			}
-
-			// flush the buffer, but don't wait indefinitely
-			timeout := make(chan struct{}, 1)
-			go func() {
-				_ = bw.Flush()
-				close(timeout)
-			}()
-
-			const waitTime = time.Second
-
-			select {
-			case <-timeout:
-			case <-time.After(waitTime):
-				logger.Warnf("unable to flush buffer - closing connection")
-			}
-		}
-
-		conn.Close()
-	}
-}
-
 func KillRunningStreams(scene *models.Scene, fileNamingAlgo models.HashAlgorithm) {
 	instance.ReadLockManager.Cancel(scene.Path)
 
@@ -94,7 +42,7 @@ func (s *SceneServer) StreamSceneDirect(scene *models.Scene, w http.ResponseWrit
 	fileNamingAlgo := config.GetInstance().GetVideoFileNamingAlgorithm()
 
 	filepath := GetInstance().Paths.Scene.GetStreamPath(scene.Path, scene.GetHash(fileNamingAlgo))
-	streamRequestCtx := NewStreamRequestContext(w, r)
+	streamRequestCtx := ffmpeg.NewStreamRequestContext(w, r)
 
 	// #2579 - hijacking and closing the connection here causes video playback to fail in Safari
 	// We trust that the request context will be closed, so we don't need to call Cancel on the