Current time for inactive timeline

src/proxy-animation.js

@@ -888,7 +888,11 @@ function autoAlignStartTime(details) {
   // 5. Let start offset be the resolved timeline time corresponding to the start of the animation attachment range.
   //    In the case of view timelines, it requires a calculation based on the proportion of the cover range.
   try {
-    startOffset = CSS.percent(fractionalStartDelay(details) * 100);
+    const startDelayFraction = fractionalStartDelay(details);
+    if (startDelayFraction === null)
+      return;
+
+    startOffset = CSS.percent(startDelayFraction * 100);
   } catch {
     // TODO: Validate supported values for range start, to avoid exceptions when resolving the values.
 
@@ -901,7 +905,11 @@ function autoAlignStartTime(details) {
   // 6. Let end offset be the resolved timeline time corresponding to the end of the animation attachment range.
   //    In the case of view timelines, it requires a calculation based on the proportion of the cover range.
   try {
-    endOffset = CSS.percent((1 - fractionalEndDelay(details)) * 100);
+    const endDelayFraction = fractionalEndDelay(details);
+    if (endDelayFraction === null)
+      return;
+
+    endOffset = CSS.percent((1 - endDelayFraction) * 100);
   } catch {
     // TODO: Validate supported values for range end, to avoid exceptions when resolving the values.
 

src/scroll-timeline-base.js

@@ -611,6 +611,9 @@ export function range(timeline, phase) {
   if (!(timeline instanceof ViewTimeline))
     return unresolved;
 
+  if (!sourceMeasurements || !subjectMeasurements)
+    return unresolved;
+
   return calculateRange(phase, sourceMeasurements, subjectMeasurements, details.axis, details.inset);
 }
 
@@ -810,7 +813,7 @@ export function fractionalOffset(timeline, value) {
 
 export function calculateRelativePosition(phaseRange, offset, coverRange, subject) {
   if (!phaseRange || !coverRange)
-    return 0;
+    return null;
 
   let style = getComputedStyle(subject)
   const info = {