Return and pass around clock skew to be used in latency calculations.

Closes #1920

controllers/status.go

@@ -3,6 +3,7 @@ package controllers
 import (
 	"encoding/json"
 	"net/http"
+	"time"
 
 	"github.com/owncast/owncast/core"
 	"github.com/owncast/owncast/router/middleware"
@@ -17,6 +18,7 @@ func GetStatus(w http.ResponseWriter, r *http.Request) {
 	response := webStatusResponse{
 		Online:             status.Online,
 		ViewerCount:        status.ViewerCount,
+		ServerTime:         time.Now(),
 		LastConnectTime:    status.LastConnectTime,
 		LastDisconnectTime: status.LastDisconnectTime,
 		VersionNumber:      status.VersionNumber,
@@ -32,9 +34,9 @@ func GetStatus(w http.ResponseWriter, r *http.Request) {
 }
 
 type webStatusResponse struct {
-	Online      bool `json:"online"`
-	ViewerCount int  `json:"viewerCount"`
-
+	Online             bool            `json:"online"`
+	ViewerCount        int             `json:"viewerCount"`
+	ServerTime         time.Time       `json:"serverTime"`
 	LastConnectTime    *utils.NullTime `json:"lastConnectTime"`
 	LastDisconnectTime *utils.NullTime `json:"lastDisconnectTime"`
 

webroot/js/app.js

@@ -319,8 +319,12 @@ export default class App extends Component {
       lastConnectTime,
       streamTitle,
       lastDisconnectTime,
+      serverTime,
     } = status;
 
+    const clockSkew = new Date(serverTime).getTime() - Date.now();
+    this.player.setClockSkew(clockSkew);
+
     this.setState({
       viewerCount,
       lastConnectTime,

webroot/js/components/latencyCompensator.js

@@ -58,6 +58,7 @@ class LatencyCompensator {
     this.playbackRate = 1.0;
     this.lastJumpOccurred = null;
     this.startupTime = new Date();
+    this.clockSkewMs = 0;
 
     this.player.on('playing', this.handlePlaying.bind(this));
     this.player.on('error', this.handleError.bind(this));
@@ -68,6 +69,15 @@ class LatencyCompensator {
     this.player.on('canplay', this.handlePlaying.bind(this));
   }
 
+  // To keep our client clock in sync with the server clock to determine
+  // accurate latency the clock skew should be set here to be used in
+  // the calculation. Otherwise if somebody's client clock is significantly
+  // off it will have a very incorrect latency determination and make bad
+  // decisions.
+  setClockSkew(skewMs) {
+    this.clockSkewMs = skewMs;
+  }
+
   // This is run on a timer to check if we should be compensating for latency.
   check() {
     // We have an arbitrary delay at startup to allow the player to run
@@ -167,7 +177,7 @@ class LatencyCompensator {
       );
 
       const segmentTime = segment.dateTimeObject.getTime();
-      const now = new Date().getTime();
+      const now = new Date().getTime() + this.clockSkewMs;
       const latency = now - segmentTime;
 
       // Since the calculation of latency is based on clock times, it's possible
@@ -190,12 +200,13 @@ class LatencyCompensator {
           latency > maxLatencyThreshold + MAX_JUMP_LATENCY
         ) {
           const jumpAmount = latency / 1000 - segment.duration * 3;
-          console.log('jump amount', jumpAmount);
           const seekPosition = this.player.currentTime() + jumpAmount;
           console.log(
             'latency',
             latency / 1000,
-            'jumping to live from ',
+            'jumping',
+            jumpAmount,
+            'to live from ',
             this.player.currentTime(),
             ' to ',
             seekPosition
@@ -253,9 +264,9 @@ class LatencyCompensator {
         this.enabled,
         'running: ',
         this.running,
-        'timeout: ',
-        this.inTimeout,
-        'buffers: ',
+        'skew: ',
+        this.clockSkewMs,
+        'rebuffer events: ',
         this.bufferingCounter
       );
     } catch (err) {

webroot/js/components/player.js

@@ -57,6 +57,8 @@ class OwncastPlayer {
     this.hasStartedPlayback = false;
     this.latencyCompensatorEnabled = false;
 
+    this.clockSkewMs = 0;
+
     // bind all the things because safari
     this.startPlayer = this.startPlayer.bind(this);
     this.handleReady = this.handleReady.bind(this);
@@ -92,6 +94,18 @@ class OwncastPlayer {
     this.vjsPlayer.ready(this.handleReady);
   }
 
+  setClockSkew(skewMs) {
+    this.clockSkewMs = skewMs;
+
+    if (this.playbackMetrics) {
+      this.playbackMetrics.setClockSkew(skewMs);
+    }
+
+    if (this.latencyCompensator) {
+      this.latencyCompensator.setClockSkew(skewMs);
+    }
+  }
+
   setupPlayerCallbacks(callbacks) {
     const { onReady, onPlaying, onEnded, onError } = callbacks;
 
@@ -116,6 +130,7 @@ class OwncastPlayer {
 
   setupPlaybackMetrics() {
     this.playbackMetrics = new PlaybackMetrics(this.vjsPlayer, videojs);
+    this.playbackMetrics.setClockSkew(this.clockSkewMs);
   }
 
   setupLatencyCompensator() {
@@ -139,6 +154,7 @@ class OwncastPlayer {
 
   startLatencyCompensator() {
     this.latencyCompensator = new LatencyCompensator(this.vjsPlayer);
+    this.playbackMetrics.setClockSkew(this.clockSkewMs);
     this.latencyCompensator.enable();
     this.latencyCompensatorEnabled = true;
     this.setLatencyCompensatorItemTitle('disable minimized latency');

webroot/js/metrics/playback.js

@@ -7,6 +7,7 @@ class PlaybackMetrics {
     this.player = player;
     this.supportsDetailedMetrics = false;
     this.hasPerformedInitialVariantChange = false;
+    this.clockSkewMs = 0;
 
     this.segmentDownloadTime = [];
     this.bandwidthTracking = [];
@@ -59,6 +60,12 @@ class PlaybackMetrics {
     }, METRICS_SEND_INTERVAL);
   }
 
+  // Keep our client clock in sync with the server clock to determine
+  // accurate latency calculations.
+  setClockSkew(skewMs) {
+    this.clockSkewMs = skewMs;
+  }
+
   videoJSReady() {
     const tech = this.player.tech({ IWillNotUseThisInPlugins: true });
     this.supportsDetailedMetrics = !!tech;
@@ -173,7 +180,7 @@ class PlaybackMetrics {
       }
 
       const segmentTime = segment.dateTimeObject.getTime();
-      const now = new Date().getTime();
+      const now = new Date().getTime() + this.clockSkewMs;
       const latency = now - segmentTime;
 
       // Throw away values that seem invalid.
@@ -237,7 +244,7 @@ class PlaybackMetrics {
     };
 
     try {
-      fetch(URL_PLAYBACK_METRICS, options);
+      await fetch(URL_PLAYBACK_METRICS, options);
     } catch (e) {
       console.error(e);
     }
@@ -249,9 +256,7 @@ export default PlaybackMetrics;
 function getCurrentlyPlayingSegment(tech, old_segment = null) {
   var target_media = tech.vhs.playlists.media();
   var snapshot_time = tech.currentTime();
-
   var segment;
-  var segment_time;
 
   // Iterate trough available segments and get first within which snapshot_time is
   for (var i = 0, l = target_media.segments.length; i < l; i++) {
@@ -263,13 +268,7 @@ function getCurrentlyPlayingSegment(tech, old_segment = null) {
   }
 
   // Null segment_time in case it's lower then 0.
-  if (segment) {
-    segment_time = Math.max(
-      0,
-      snapshot_time - (segment.end - segment.duration)
-    );
-    // Because early segments don't have end property
-  } else {
+  if (!segment) {
     segment = target_media.segments[0];
     segment_time = 0;
   }