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"use strict";
(() => {
const randomBackoffMilliseconds = (lowest, highest) => {
return Math.round(Math.random() * (highest - lowest) + lowest);
};
const prepareInitialInfoMessage = () => {
const dataView = new DataView(new ArrayBuffer(1));
dataView.setUint8(0, "i".charCodeAt(0));
return dataView;
};
const prepareStateUpdateMessage = (positionMilliseconds, paused) => {
const dataView = new DataView(new ArrayBuffer(10));
dataView.setUint8(0, "s".charCodeAt(0));
dataView.setUint8(1, +paused);
dataView.setBigUint64(2, positionMilliseconds);
return dataView;
};
const player = videojs("player", {
controls: true,
fill: true,
playsinline: true,
preload: "auto",
});
const updatePlaybackState = (latestReceivedState, nowMilliseconds) => {
if (nowMilliseconds - latestReceivedState.receivedAtMilliseconds > 2000) {
player.pause();
return;
}
const idealPositionMilliseconds =
latestReceivedState.positionMilliseconds +
(nowMilliseconds - latestReceivedState.receivedAtMilliseconds);
const currentPositionMilliseconds = player.currentTime() * 1000;
const positionDiffMilliseconds = currentPositionMilliseconds - idealPositionMilliseconds;
const absPositionDiffMilliseconds = Math.abs(positionDiffMilliseconds);
if (absPositionDiffMilliseconds > 1250) {
player.currentTime(idealPositionMilliseconds / 1000);
player.playbackRate(1);
} else if (
absPositionDiffMilliseconds > 200 ||
(player.playbackRate() != 1 && absPositionDiffMilliseconds > 100)
) {
player.playbackRate(1 - 0.02 * Math.sign(positionDiffMilliseconds));
} else {
player.playbackRate(1);
}
if (latestReceivedState.paused) {
player.pause();
player.currentTime(idealPositionMilliseconds / 1000);
} else {
player.play().then(null, () => {
// Failed to play - try muting in case it's because the browser is blocking autoplay
player.muted(true);
player.play().then(null, () => console.error("Failed to play video."));
});
}
};
const latestReceivedState = {
paused: true,
positionMilliseconds: 0,
receivedAtMilliseconds: null,
};
const manageWebsocket = () => {
let websocket = new WebSocket(location.href.replace(/^http/, "ws") + "/websocket");
websocket.binaryType = "arraybuffer";
let initialized = false;
let host;
// Interval to check video state for non-hosts, and to send state for host
let intervalId;
websocket.addEventListener("open", (_) => {
console.debug("Created WebSocket connection successfully.");
websocket.send(prepareInitialInfoMessage());
});
websocket.addEventListener("message", (event) => {
const messageDataView = new DataView(event.data);
switch (String.fromCharCode(messageDataView.getUint8(0))) {
case "i":
if (initialized) {
websocket.close(); // Error condition: we're already initialized
} else {
initialized = true;
host = !!messageDataView.getUint8(1);
// How often host sends state - unused on non-host clients
const SEND_STATE_INTERVAL_MILLISECONDS = 250;
// How often client checks if its state matches what the server sent - unused on hosts
const CHECK_STATE_INTERVAL_MILLISECONDS = 20;
if (host) {
intervalId = setInterval(() => {
websocket.send(
prepareStateUpdateMessage(
BigInt(Math.round(player.currentTime() * 1000)),
player.paused(),
),
);
}, SEND_STATE_INTERVAL_MILLISECONDS);
} else {
intervalId = setInterval(() => {
updatePlaybackState(latestReceivedState, performance.now());
}, CHECK_STATE_INTERVAL_MILLISECONDS);
}
}
break;
case "s":
if (host || !initialized) {
/* Error conditions: host should send state updates, not receive
them, and the server should not send us state updates until
we're initialized. */
websocket.close();
} else {
latestReceivedState.paused = messageDataView.getUint8(1);
latestReceivedState.positionMilliseconds = Number(messageDataView.getBigUint64(2));
latestReceivedState.receivedAtMilliseconds = performance.now();
}
break;
default:
websocket.close(); // Error condition: unrecognized message type
}
});
websocket.addEventListener("close", (_) => {
clearInterval(intervalId);
player.pause();
const recreateAfter = randomBackoffMilliseconds(50, 3000);
console.debug(
`WebSocket connection closed; will attempt to recreate it in ${recreateAfter} ms.`,
);
websocket = null;
setTimeout(manageWebsocket, recreateAfter);
});
};
manageWebsocket();
})();
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