Retire cancelled playback sessions and preserve VOD content time

Adapted from MikaelKW/nodecast-tv-plus playback lease work beginning at 43a58c7685f541498663b827c4b9d6b3753e7202. Reject superseded requests, release on cancellation, bound live restart attempts and await FFmpeg close before deleting cache.

Co-authored-by: Mikael <mikaelkwessel@gmail.com>

public/js/components/PlaybackSessions.js

@@ -0,0 +1,52 @@
+(function (root) {
+    const cancelled = () => Object.assign(new Error('Playback was superseded'), { name: 'AbortError' });
+    class PlaybackSessions {
+        constructor(isLive) {
+            this.isLive = isLive;
+            this.leaseId = null;
+            this.sequence = 0;
+            this.controller = null;
+            this.timer = null;
+            root.addEventListener?.('pagehide', () => this.stop());
+        }
+        async create(url, options) {
+            this.leaseId ||= root.crypto.randomUUID?.() || Array.from(root.crypto.getRandomValues(new Uint8Array(16)),
+                byte => byte.toString(16).padStart(2, '0')).join('');
+            const leaseId = this.leaseId, sequence = ++this.sequence;
+            this.controller?.abort();
+            const controller = this.controller = new AbortController();
+            const response = await fetch('/api/transcode/session', {
+                method: 'POST', credentials: 'same-origin', signal: controller.signal,
+                headers: { 'Content-Type': 'application/json' },
+                body: JSON.stringify({ ...options, url, isLive: this.isLive, playbackLeaseId: leaseId, requestSequence: sequence })
+            });
+            const session = await response.json();
+            if (controller.signal.aborted || leaseId !== this.leaseId || sequence !== this.sequence) {
+                if (session.sessionId) fetch(`/api/transcode/${session.sessionId}`, { method: 'DELETE', keepalive: true }).catch(() => {});
+                throw cancelled();
+            }
+            if (!response.ok) throw new Error(session.error || 'Unable to start playback');
+            this.timer ||= setInterval(() => {
+                if (this.leaseId) fetch('/api/transcode/lease/heartbeat', {
+                    method: 'POST', headers: { 'Content-Type': 'application/json' },
+                    body: JSON.stringify({ playbackLeaseId: this.leaseId })
+                }).catch(() => {});
+            }, 30000);
+            return session;
+        }
+        stop() {
+            const leaseId = this.leaseId;
+            this.leaseId = null;
+            this.sequence++;
+            this.controller?.abort();
+            this.controller = null;
+            clearInterval(this.timer);
+            this.timer = null;
+            if (leaseId) fetch('/api/transcode/lease', {
+                method: 'DELETE', keepalive: true, headers: { 'Content-Type': 'application/json' },
+                body: JSON.stringify({ playbackLeaseId: leaseId })
+            }).catch(() => {});
+        }
+    }
+    root.PlaybackSessions = PlaybackSessions;
+}(typeof window === 'object' ? window : globalThis));