Save and load the position for the video using a local storage object, the object is a dictionary, where the key is the video ID, and the value is the time at which the user last left off watching the video. If the user deselected the 'remember video position' checkbox in the preferences this dictionary is cleared

assets/js/player.js

@@ -38,6 +38,8 @@ embed_url.searchParams.delete('v');
 short_url = location.origin + '/' + video_data.id + embed_url.search;
 embed_url = location.origin + '/embed/' + video_data.id + embed_url.search;
 
+var remember_position_key = "remember_position";
+
 var shareOptions = {
     socials: ['fbFeed', 'tw', 'reddit', 'email'],
 
@@ -199,6 +201,27 @@ if (video_data.premiere_timestamp && Math.round(new Date() / 1000) < video_data.
     player.getChild('bigPlayButton').hide();
 }
 
+if (video_data.params.remember_position) {
+    const remeberedTime = get_video_time();
+    let lastUpdated = 0;
+
+    set_seconds_after_start(remeberedTime);
+
+    player.on("timeupdate", e => {
+        const raw = player.currentTime();
+        const time = Math.floor(raw);
+
+        if(lastUpdated !== time) {
+            save_video_time(time);
+            lastUpdated = time;
+        }
+    });
+}
+else {
+    console.log("Removing data for remebered positions");
+    remove_all_video_times();
+}
+
 if (video_data.params.autoplay) {
     var bpb = player.getChild('bigPlayButton');
     bpb.hide();
@@ -330,6 +353,55 @@ function skip_seconds(delta) {
     player.currentTime(newTime);
 }
 
+function set_seconds_after_start(delta) {
+    const start = video_data.params.video_start;
+    player.currentTime(start + delta);
+}
+
+function save_video_time(seconds) {
+    const videoId = video_data.id;
+    const all_video_times = get_all_video_times();
+
+    all_video_times[videoId] = seconds;
+
+    set_all_video_times(all_video_times);
+}
+
+function get_video_time() {
+    try {
+        const videoId = video_data.id;
+        const all_video_times = get_all_video_times();
+        const timestamp = all_video_times[videoId];
+
+        return timestamp;
+    }
+    catch {
+        return 0;
+    }
+}
+
+function set_all_video_times(times) {
+    const json = JSON.stringify(times);
+
+    localStorage.setItem(remember_position_key, json);
+}
+
+function get_all_video_times() {
+    try {
+        const raw = localStorage.getItem(remember_position_key);
+        const times = JSON.parse(raw);
+
+        return times || {};
+    }
+    catch {
+        return {};
+    }
+}
+
+function remove_all_video_times() {
+    localStorage.removeItem(remember_position_key);
+}
+
 function set_time_percent(percent) {
     const duration = player.duration();
     const newTime = duration * (percent / 100);