1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
|
"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",
});
player.controlBar.progressControl.disable();
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) {
player.controlBar.progressControl.enable();
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();
})();
|
