Introduce basic audio playback control

src/components/views/audio_messages/DurationClock.tsx

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+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import React from "react";
+import { replaceableComponent } from "../../../utils/replaceableComponent";
+import Clock from "./Clock";
+import { Playback } from "../../../voice/Playback";
+
+interface IProps {
+    playback: Playback;
+}
+
+interface IState {
+    durationSeconds: number;
+}
+
+/**
+ * A clock which shows a clip's maximum duration.
+ */
+@replaceableComponent("views.audio_messages.DurationClock")
+export default class DurationClock extends React.PureComponent<IProps, IState> {
+    public constructor(props) {
+        super(props);
+
+        this.state = {
+            // we track the duration on state because we won't really know what the clip duration
+            // is until the first time update, and as a PureComponent we are trying to dedupe state
+            // updates as much as possible. This is just the easiest way to avoid a forceUpdate() or
+            // member property to track "did we get a duration".
+            durationSeconds: this.props.playback.clockInfo.durationSeconds,
+        };
+        this.props.playback.clockInfo.liveData.onUpdate(this.onTimeUpdate);
+    }
+
+    private onTimeUpdate = (time: number[]) => {
+        this.setState({durationSeconds: time[1]});
+    };
+
+    public render() {
+        return <Clock seconds={this.state.durationSeconds} />;
+    }
+}