Fix live playback on WebOS (#3750) (#3754)

* Fix live playback on WebOS (#3750)

Reverts some of the changes made in:
a66913f (Timeline and multiperiod optimizations (#3413), 2021-04-23)

* [Settings] Add enableSeekDecorrelationFix

Allows disabling the workaround for live playback start (#3750)

Author: lkinasiewicz

index.d.ts

@@ -176,6 +176,7 @@ declare namespace dashjs {
                 keepProtectionMediaKeys?: boolean,
             },
             buffer?: {
+                enableSeekDecorrelationFix?: boolean,
                 fastSwitchEnabled?: boolean,
                 flushBufferAtTrackSwitch?: boolean,
                 reuseExistingSourceBuffers?: boolean,

src/core/Settings.js

@@ -84,6 +84,7 @@ import {HTTPRequest} from '../streaming/vo/metrics/HTTPRequest';
  *                keepProtectionMediaKeys: false
  *            },
  *            buffer: {
+                  enableSeekDecorrelationFix: true,
  *                fastSwitchEnabled: true,
  *                flushBufferAtTrackSwitch: false,
  *                reuseExistingSourceBuffers: true,
@@ -239,6 +240,11 @@ import {HTTPRequest} from '../streaming/vo/metrics/HTTPRequest';
 
 /**
  * @typedef {Object} Buffer
+ * @property {boolean} [enableSeekDecorrelationFix=true]
+ * Enables a workaround for playback start on some devices, e.g. WebOS 4.9.
+ * It is necessary because some browsers do not support setting currentTime on video element to a value that is outside of current buffer.
+ *
+ * If you experience unexpected seeking triggered by BufferController, you can try setting this value to false.
  * @property {boolean} [fastSwitchEnabled=true]
  * When enabled, after an ABR up-switch in quality, instead of requesting and appending the next fragment at the end of the current buffer range it is requested and appended closer to the current time.
  *
@@ -761,6 +767,7 @@ function Settings() {
                 keepProtectionMediaKeys: false
             },
             buffer: {
+                enableSeekDecorrelationFix: true,
                 fastSwitchEnabled: true,
                 flushBufferAtTrackSwitch: false,
                 reuseExistingSourceBuffers: true,

src/streaming/controllers/BufferController.js

@@ -346,7 +346,17 @@ function BufferController(config) {
         range = getRangeAt(seekTarget, segmentDuration);
         if (!range) return;
 
-        if (currentTime < range.start) {
+        if (settings.get().streaming.buffer.enableSeekDecorrelationFix && Math.abs(currentTime - seekTarget) > segmentDuration) {
+            // If current video model time is decorrelated from seek target (and appended buffer) then seek video element
+            // (in case of live streams on some browsers/devices for which we can't set video element time at unavalaible range)
+
+            // Check if appended segment is not anterior from seek target (segments timeline/template tolerance)
+            if (seekTarget <= range.end) {
+                // Seek video element to seek target or range start if appended buffer starts after seek target (segments timeline/template tolerance)
+                playbackController.seek(Math.max(seekTarget, range.start), false, true);
+                seekTarget = NaN;
+            }
+        } else if (currentTime < range.start) {
             // If appended buffer starts after seek target (segments timeline/template tolerance) then seek to range start
             playbackController.seek(range.start, false, true);
             seekTarget = NaN;