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diff --git a/ext/js/media/media-util.js b/ext/js/media/media-util.js
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+/*
+ * Copyright (C) 2020-2021  Yomichan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/**
+ * MediaUtil is a class containing helper methods related to media processing.
+ */
+class MediaUtil {
+    /**
+     * Gets the file extension of a file path. URL search queries and hash
+     * fragments are not handled.
+     * @param path The path to the file.
+     * @returns The file extension, including the '.', or an empty string
+     *   if there is no file extension.
+     */
+    getFileNameExtension(path) {
+        const match = /\.[^./\\]*$/.exec(path);
+        return match !== null ? match[0] : '';
+    }
+
+    /**
+     * Gets an image file's media type using a file path.
+     * @param path The path to the file.
+     * @returns The media type string if it can be determined from the file path,
+     *   otherwise null.
+     */
+    getImageMediaTypeFromFileName(path) {
+        switch (this.getFileNameExtension(path).toLowerCase()) {
+            case '.apng':
+                return 'image/apng';
+            case '.bmp':
+                return 'image/bmp';
+            case '.gif':
+                return 'image/gif';
+            case '.ico':
+            case '.cur':
+                return 'image/x-icon';
+            case '.jpg':
+            case '.jpeg':
+            case '.jfif':
+            case '.pjpeg':
+            case '.pjp':
+                return 'image/jpeg';
+            case '.png':
+                return 'image/png';
+            case '.svg':
+                return 'image/svg+xml';
+            case '.tif':
+            case '.tiff':
+                return 'image/tiff';
+            case '.webp':
+                return 'image/webp';
+            default:
+                return null;
+        }
+    }
+
+    /**
+     * Gets the file extension for a corresponding media type.
+     * @param mediaType The media type to use.
+     * @returns A file extension including the dot for the media type,
+     *   otherwise null.
+     */
+    getFileExtensionFromImageMediaType(mediaType) {
+        switch (mediaType) {
+            case 'image/apng':
+                return '.apng';
+            case 'image/bmp':
+                return '.bmp';
+            case 'image/gif':
+                return '.gif';
+            case 'image/x-icon':
+                return '.ico';
+            case 'image/jpeg':
+                return '.jpeg';
+            case 'image/png':
+                return '.png';
+            case 'image/svg+xml':
+                return '.svg';
+            case 'image/tiff':
+                return '.tiff';
+            case 'image/webp':
+                return '.webp';
+            default:
+                return null;
+        }
+    }
+
+    /**
+     * Gets the file extension for a corresponding media type.
+     * @param mediaType The media type to use.
+     * @returns A file extension including the dot for the media type,
+     *   otherwise null.
+     */
+    getFileExtensionFromAudioMediaType(mediaType) {
+        switch (mediaType) {
+            case 'audio/mpeg':
+            case 'audio/mp3':
+                return '.mp3';
+            case 'audio/mp4':
+                return '.mp4';
+            case 'audio/ogg':
+            case 'audio/vorbis':
+                return '.ogg';
+            case 'audio/vnd.wav':
+            case 'audio/wave':
+            case 'audio/wav':
+            case 'audio/x-wav':
+            case 'audio/x-pn-wav':
+                return '.wav';
+            case 'audio/flac':
+                return '.flac';
+            case 'audio/webm':
+                return '.webm';
+            default:
+                return null;
+        }
+    }
+}