fix: calculate EXT-X-START TIME-OFFSET from actual playlist end for live streams

src/playlist-controller.js

@@ -1221,7 +1221,15 @@ export class PlaylistController extends videojs.EventTarget {
         const offset = media.start.timeOffset;
 
         if (offset < 0) {
-          startPoint = Math.max(seekableEnd + offset, seekable.start(0));
+          // Per HLS spec, negative TIME-OFFSET is from the end of the last Media Segment.
+          // For live streams, seekableEnd already has liveEdgeDelay subtracted,
+          // so we need to add it back to get the actual playlist end.
+          // Clamp to seekableEnd to avoid seeking into the unsafe live edge zone.
+          const main = this.mainPlaylistLoader_.main;
+          const liveEdgeDelay = Vhs.Playlist.liveEdgeDelay(main, media);
+          const actualPlaylistEnd = seekableEnd + liveEdgeDelay;
+
+          startPoint = Math.max(Math.min(actualPlaylistEnd + offset, seekableEnd), seekable.start(0));
         } else {
           startPoint = Math.min(seekableEnd, offset);
         }

test/manifests/startLiveNegative.m3u8

@@ -0,0 +1,15 @@
+#EXTM3U
+#EXT-X-START:TIME-OFFSET=-30,PRECISE=YES
+#EXT-X-TARGETDURATION:10
+#EXTINF:10,
+media-00001.ts
+#EXTINF:10,
+media-00002.ts
+#EXTINF:10,
+media-00003.ts
+#EXTINF:10,
+media-00004.ts
+#EXTINF:10,
+media-00005.ts
+#EXTINF:10,
+media-00006.ts

test/videojs-http-streaming.test.js

@@ -485,6 +485,30 @@ QUnit.test('seeks to negative offset point', function(assert) {
   assert.strictEqual(currentTime, 35, 'seeked to negative offset');
 });
 
+QUnit.test('seeks to negative offset on live stream from actual playlist end', function(assert) {
+  let currentTime = 0;
+
+  this.player.autoplay(true);
+  this.player.on('seeking', () => {
+    currentTime = this.player.currentTime();
+  });
+  this.player.src({
+    src: 'startLiveNegative.m3u8',
+    type: 'application/vnd.apple.mpegurl'
+  });
+
+  this.clock.tick(1);
+
+  openMediaSource(this.player, this.clock);
+  this.player.tech_.trigger('play');
+  this.standardXHRResponse(this.requests.shift());
+  this.clock.tick(1);
+
+  // 6 segments * 10s = 60s total, liveEdgeDelay = 30, TIME-OFFSET = -30
+  // Per HLS spec, offset is from playlist end (60s), so startPoint = 60 - 30 = 30
+  assert.strictEqual(currentTime, 30, 'seeked to negative offset from actual playlist end on live stream');
+});
+
 QUnit.test(
   'duration is set when the source opens after the playlist is loaded',
   function(assert) {