js: add support for keydown events (#678)

* js: add support for keydown events

This will modify the player behavior even if the player element is unfocused.

Based on the YouTube key bindings, allow to

- toggle playback with space and 'k' key
- increase and decrease player volume with up / down arrow key
- mute and unmute player with 'm' key
- jump forwards and backwards by 5 seconds with right / left arrow key
- jump forwards and backwards by 10 seconds with 'l' / 'j'  key
- set video progress with number keys 0–9
- toggle captions with 'c' key
- toggle fullscreen mode with 'f' key
- play next video with 'N' key
- increase and decrease playback speed with '>' / '<' key

* js: remove unused dependency 'videojs.hotkeys.min.js'

Support for controlling the player volume by scrolling over it is
still retained by copying over the relevant code part from the
aforementioned library.

assets/js/player.js

@@ -38,69 +38,7 @@ var shareOptions = {
     embedCode: "<iframe id='ivplayer' type='text/html' width='640' height='360' src='" + embed_url + "' frameborder='0'></iframe>"
 }
 
-var player = videojs('player', options, function () {
-    this.hotkeys({
-        volumeStep: 0.1,
-        seekStep: 5,
-        enableModifiersForNumbers: false,
-        enableHoverScroll: true,
-        customKeys: {
-            // Toggle play with K Key
-            play: {
-                key: function (e) {
-                    return e.which === 75;
-                },
-                handler: function (player, options, e) {
-                    if (player.paused()) {
-                        player.play();
-                    } else {
-                        player.pause();
-                    }
-                }
-            },
-            // Go backward 10 seconds
-            backward: {
-                key: function (e) {
-                    return e.which === 74;
-                },
-                handler: function (player, options, e) {
-                    player.currentTime(player.currentTime() - 10);
-                }
-            },
-            // Go forward 10 seconds
-            forward: {
-                key: function (e) {
-                    return e.which === 76;
-                },
-                handler: function (player, options, e) {
-                    player.currentTime(player.currentTime() + 10);
-                }
-            },
-            // Increase speed
-            increase_speed: {
-                key: function (e) {
-                    return (e.which === 190 && e.shiftKey);
-                },
-                handler: function (player, _, e) {
-                    size = options.playbackRates.length;
-                    index = options.playbackRates.indexOf(player.playbackRate());
-                    player.playbackRate(options.playbackRates[(index + 1) % size]);
-                }
-            },
-            // Decrease speed
-            decrease_speed: {
-                key: function (e) {
-                    return (e.which === 188 && e.shiftKey);
-                },
-                handler: function (player, _, e) {
-                    size = options.playbackRates.length;
-                    index = options.playbackRates.indexOf(player.playbackRate());
-                    player.playbackRate(options.playbackRates[(size + index - 1) % size]);
-                }
-            }
-        }
-    });
-});
+var player = videojs('player', options);
 
 if (location.pathname.startsWith('/embed/')) {
     player.overlay({
@@ -254,5 +192,273 @@ if (!video_data.params.listen && video_data.params.annotations) {
     xhr.send();
 }
 
+function increase_volume(delta) {
+    const curVolume = player.volume();
+    let newVolume = curVolume + delta;
+    if (newVolume > 1) {
+        newVolume = 1;
+    } else if (newVolume < 0) {
+        newVolume = 0;
+    }
+    player.volume(newVolume);
+}
+
+function toggle_muted() {
+    const isMuted = player.muted();
+    player.muted(!isMuted);
+}
+
+function skip_seconds(delta) {
+    const duration = player.duration();
+    const curTime = player.currentTime();
+    let newTime = curTime + delta;
+    if (newTime > duration) {
+        newTime = duration;
+    } else if (newTime < 0) {
+        newTime = 0;
+    }
+    player.currentTime(newTime);
+}
+
+function set_time_percent(percent) {
+    const duration = player.duration();
+    const newTime = duration * (percent / 100);
+    player.currentTime(newTime);
+}
+
+function toggle_play() {
+    if (player.paused()) {
+        player.play();
+    } else {
+        player.pause();
+    }
+}
+
+const toggle_captions = (function() {
+    let toggledTrack = null;
+    const onChange = function(e) {
+        toggledTrack = null;
+    };
+    const bindChange = function(onOrOff) {
+        player.textTracks()[onOrOff]('change', onChange);
+    };
+    // Wrapper function to ignore our own emitted events and only listen
+    // to events emitted by Video.js on click on the captions menu items.
+    const setMode = function(track, mode) {
+        bindChange('off');
+        track.mode = mode;
+        window.setTimeout(function() {
+            bindChange('on');
+        }, 0);
+    };
+    bindChange('on');
+    return function() {
+        if (toggledTrack !== null) {
+            if (toggledTrack.mode !== 'showing') {
+                setMode(toggledTrack, 'showing');
+            } else {
+                setMode(toggledTrack, 'disabled');
+            }
+            toggledTrack = null;
+            return;
+        }
+
+        // Used as a fallback if no captions are currently active.
+        // TODO: Make this more intelligent by e.g. relying on browser language.
+        let fallbackCaptionsTrack = null;
+
+        const tracks = player.textTracks();
+        for (let i = 0; i < tracks.length; i++) {
+            const track = tracks[i];
+            if (track.kind !== 'captions') {
+                continue;
+            }
+
+            if (fallbackCaptionsTrack === null) {
+                fallbackCaptionsTrack = track;
+            }
+            if (track.mode === 'showing') {
+                setMode(track, 'disabled');
+                toggledTrack = track;
+                return;
+            }
+        }
+
+        // Fallback if no captions are currently active.
+        if (fallbackCaptionsTrack !== null) {
+            setMode(fallbackCaptionsTrack, 'showing');
+            toggledTrack = fallbackCaptionsTrack;
+        }
+    };
+})();
+
+function toggle_fullscreen() {
+    if (player.isFullscreen()) {
+        player.exitFullscreen();
+    } else {
+        player.requestFullscreen();
+    }
+}
+
+function increase_playback_rate(steps) {
+    const maxIndex = options.playbackRates.length - 1;
+    const curIndex = options.playbackRates.indexOf(player.playbackRate());
+    let newIndex = curIndex + steps;
+    if (newIndex > maxIndex) {
+        newIndex = maxIndex;
+    } else if (newIndex < 0) {
+        newIndex = 0;
+    }
+    player.playbackRate(options.playbackRates[newIndex]);
+}
+
+window.addEventListener('keydown', e => {
+    if (e.target.tagName.toLowerCase() === 'input') {
+        // Ignore input when focus is on certain elements, e.g. form fields.
+        return;
+    }
+    // See https://github.com/ctd1500/videojs-hotkeys/blob/bb4a158b2e214ccab87c2e7b95f42bc45c6bfd87/videojs.hotkeys.js#L310-L313
+    const isPlayerFocused = false
+        || e.target === document.querySelector('.video-js')
+        || e.target === document.querySelector('.vjs-tech')
+        || e.target === document.querySelector('.iframeblocker')
+        || e.target === document.querySelector('.vjs-control-bar')
+    ;
+    let action = null;
+
+    const code = e.keyCode;
+    const key = e.key;
+    switch (key) {
+    case ' ':
+    case 'k':
+        action = toggle_play;
+        break;
+
+    case 'ArrowUp':
+        if (isPlayerFocused) {
+            action = increase_volume.bind(this, 0.1);
+        }
+        break;
+    case 'ArrowDown':
+        if (isPlayerFocused) {
+            action = increase_volume.bind(this, -0.1);
+        }
+        break;
+
+    case 'm':
+        action = toggle_muted;
+        break;
+
+    case 'ArrowRight':
+        action = skip_seconds.bind(this, 5);
+        break;
+    case 'ArrowLeft':
+        action = skip_seconds.bind(this, -5);
+        break;
+    case 'l':
+        action = skip_seconds.bind(this, 10);
+        break;
+    case 'j':
+        action = skip_seconds.bind(this, -10);
+        break;
+
+    case '0':
+    case '1':
+    case '2':
+    case '3':
+    case '4':
+    case '5':
+    case '6':
+    case '7':
+    case '8':
+    case '9':
+        const percent = (code - 48) * 10;
+        action = set_time_percent.bind(this, percent);
+        break;
+
+    case 'c':
+        action = toggle_captions;
+        break;
+    case 'f':
+        action = toggle_fullscreen;
+        break;
+
+    case 'N':
+        action = next_video;
+        break;
+    case 'P':
+        // TODO: Add support to play back previous video.
+        break;
+
+    case '.':
+        // TODO: Add support for next-frame-stepping.
+        break;
+    case ',':
+        // TODO: Add support for previous-frame-stepping.
+        break;
+
+    case '>':
+        action = increase_playback_rate.bind(this, 1);
+        break;
+    case '<':
+        action = increase_playback_rate.bind(this, -1);
+        break;
+
+    default:
+        console.info('Unhandled key down event: %s:', key, e);
+        break;
+    }
+
+    if (action) {
+        e.preventDefault();
+        action();
+    }
+}, false);
+
+// Add support for controlling the player volume by scrolling over it. Adapted from
+// https://github.com/ctd1500/videojs-hotkeys/blob/bb4a158b2e214ccab87c2e7b95f42bc45c6bfd87/videojs.hotkeys.js#L292-L328
+(function() {
+    const volumeStep = 0.05;
+    const enableVolumeScroll = true;
+    const enableHoverScroll = true;
+    const doc = document;
+    const pEl = document.getElementById('player');
+
+    var volumeHover = false;
+    var volumeSelector = pEl.querySelector('.vjs-volume-menu-button') || pEl.querySelector('.vjs-volume-panel');
+    if (volumeSelector != null) {
+      volumeSelector.onmouseover = function() { volumeHover = true; };
+      volumeSelector.onmouseout = function() { volumeHover = false; };
+    }
+
+    var mouseScroll = function mouseScroll(event) {
+      var activeEl = doc.activeElement;
+      if (enableHoverScroll) {
+        // If we leave this undefined then it can match non-existent elements below
+        activeEl = 0;
+      }
+
+      // When controls are disabled, hotkeys will be disabled as well
+      if (player.controls()) {
+        if (volumeHover) {
+          if (enableVolumeScroll) {
+            event = window.event || event;
+            var delta = Math.max(-1, Math.min(1, (event.wheelDelta || -event.detail)));
+            event.preventDefault();
+
+            if (delta == 1) {
+              increase_volume(volumeStep);
+            } else if (delta == -1) {
+              increase_volume(-volumeStep);
+            }
+          }
+        }
+      }
+    };
+
+    player.on('mousewheel', mouseScroll);
+    player.on("DOMMouseScroll", mouseScroll);
+}());
+
 // Since videojs-share can sometimes be blocked, we defer it until last
 player.share(shareOptions);