diff --git a/apps/website/docs/api/classes/FFmpeg.md b/apps/website/docs/api/classes/FFmpeg.md
index faf0400..5d5fa9a 100644
--- a/apps/website/docs/api/classes/FFmpeg.md
+++ b/apps/website/docs/api/classes/FFmpeg.md
@@ -28,7 +28,7 @@ const ffmpeg = new FFmpeg();
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:97](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L97)
+[packages/ffmpeg/src/classes.ts:99](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L99)
 
 ## Properties
 
@@ -38,7 +38,7 @@ const ffmpeg = new FFmpeg();
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:95](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L95)
+[packages/ffmpeg/src/classes.ts:95](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L95)
 
 ___
 
@@ -51,7 +51,7 @@ be called when we receive message from web worker.
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:94](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L94)
+[packages/ffmpeg/src/classes.ts:94](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L94)
 
 ___
 
@@ -61,7 +61,17 @@ ___
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:88](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L88)
+[packages/ffmpeg/src/classes.ts:88](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L88)
+
+___
+
+### loaded
+
+• **loaded**: `boolean` = `false`
+
+#### Defined in
+
+[packages/ffmpeg/src/classes.ts:97](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L97)
 
 ___
 
@@ -121,7 +131,7 @@ node_modules/@types/node/events.d.ts:290
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:84](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L84)
+[packages/ffmpeg/src/classes.ts:84](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L84)
 
 ___
 
@@ -131,7 +141,7 @@ ___
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:85](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L85)
+[packages/ffmpeg/src/classes.ts:85](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L85)
 
 ___
 
@@ -141,7 +151,7 @@ ___
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:86](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L86)
+[packages/ffmpeg/src/classes.ts:86](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L86)
 
 ## Event Methods
 
@@ -172,7 +182,7 @@ ffmpeg.on(FFmpeg.DOWNLOAD, ({ url, total, received, delta, done }) => {
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:33](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L33)
+[packages/ffmpeg/src/classes.ts:33](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L33)
 
 ▸ **on**(`event`, `listener`): [`FFmpeg`](FFmpeg.md)
 
@@ -203,7 +213,7 @@ log includes output to stdout and stderr.
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:52](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L52)
+[packages/ffmpeg/src/classes.ts:52](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L52)
 
 ▸ **on**(`event`, `listener`): [`FFmpeg`](FFmpeg.md)
 
@@ -235,7 +245,7 @@ input and output video/audio file are the same.
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:69](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L69)
+[packages/ffmpeg/src/classes.ts:69](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L69)
 
 ___
 
@@ -278,7 +288,7 @@ const data = ffmpeg.readFile("video.mp4");
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:197](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L197)
+[packages/ffmpeg/src/classes.ts:202](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L202)
 
 ___
 
@@ -303,7 +313,7 @@ as it initializes WebAssembly and other essential variables.
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:166](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L166)
+[packages/ffmpeg/src/classes.ts:171](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L171)
 
 ___
 
@@ -320,7 +330,7 @@ Terminate all ongoing API calls and terminate web worker.
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:218](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L218)
+[packages/ffmpeg/src/classes.ts:223](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L223)
 
 ___
 
@@ -344,7 +354,7 @@ Create a directory.
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:315](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L315)
+[packages/ffmpeg/src/classes.ts:321](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L321)
 
 ___
 
@@ -366,7 +376,7 @@ Delete an empty directory.
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:337](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L337)
+[packages/ffmpeg/src/classes.ts:343](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L343)
 
 ___
 
@@ -388,13 +398,13 @@ Delete a file.
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:293](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L293)
+[packages/ffmpeg/src/classes.ts:299](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L299)
 
 ___
 
 ### listDir
 
-▸ **listDir**(`path`): `Promise`<`FFFSPaths`\>
+▸ **listDir**(`path`): `Promise`<`FSNode`[]\>
 
 List directory contents.
 
@@ -406,11 +416,11 @@ List directory contents.
 
 #### Returns
 
-`Promise`<`FFFSPaths`\>
+`Promise`<`FSNode`[]\>
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:326](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L326)
+[packages/ffmpeg/src/classes.ts:332](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L332)
 
 ___
 
@@ -441,7 +451,7 @@ const data = await ffmpeg.readFile("video.mp4");
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:272](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L272)
+[packages/ffmpeg/src/classes.ts:278](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L278)
 
 ___
 
@@ -464,7 +474,7 @@ Rename a file or directory.
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:304](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L304)
+[packages/ffmpeg/src/classes.ts:310](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L310)
 
 ___
 
@@ -496,7 +506,7 @@ await ffmpeg.writeFile("text.txt", "hello world");
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:246](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L246)
+[packages/ffmpeg/src/classes.ts:252](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L252)
 
 ___
 
@@ -514,7 +524,7 @@ register worker message event handlers.
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:104](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L104)
+[packages/ffmpeg/src/classes.ts:106](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L106)
 
 ___
 
@@ -537,7 +547,7 @@ Generic function to send messages to web worker.
 
 #### Defined in
 
-[packages/ffmpeg/src/classes.ts:143](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/1582ee2/packages/ffmpeg/src/classes.ts#L143)
+[packages/ffmpeg/src/classes.ts:148](https://github.com/ffmpegwasm/ffmpeg.wasm/blob/4a950d7/packages/ffmpeg/src/classes.ts#L148)
 
 ___
 
diff --git a/apps/website/src/components/Playground/CoreSelector.tsx b/apps/website/src/components/Playground/CoreSelector.tsx
deleted file mode 100644
index fd47da7..0000000
--- a/apps/website/src/components/Playground/CoreSelector.tsx
+++ /dev/null
@@ -1,53 +0,0 @@
-import * as React from "react";
-import Button from "@mui/material/Button";
-import Container from "@mui/material/Container";
-import Radio from "@mui/material/Radio";
-import RadioGroup from "@mui/material/RadioGroup";
-import FormControlLabel from "@mui/material/FormControlLabel";
-import FormControl from "@mui/material/FormControl";
-import FormLabel from "@mui/material/FormLabel";
-import styles from "./styles.module.css";
-
-interface CoreSelectorProps {
-  option: string;
-  onChange: (event: React.ChangeEvent<HTMLInputElement>) => any;
-  onSubmit: () => any;
-}
-export default function CoreSelector({
-  option,
-  onChange,
-  onSubmit,
-}: CoreSelectorProps) {
-  return (
-    <Container className={styles.margin}>
-      <Container className={styles.margin}>
-        <FormControl>
-          <FormLabel id="core-selector">Select a Core Option</FormLabel>
-          <RadioGroup
-            aria-labelledby="core-selector"
-            name="core-selector"
-            value={option}
-            onChange={onChange}
-          >
-            <FormControlLabel
-              value="core"
-              control={<Radio />}
-              label="Core (Slower, but stable)"
-            />
-            <FormControlLabel
-              value="core-mt"
-              disabled={typeof SharedArrayBuffer !== "function"}
-              control={<Radio />}
-              label="Core Multi-threaded (Faster, but lower compatibility and unstable)"
-            />
-          </RadioGroup>
-        </FormControl>
-      </Container>
-      <Container>
-        <Button variant="contained" onClick={onSubmit}>
-          Load
-        </Button>
-      </Container>
-    </Container>
-  );
-}
diff --git a/apps/website/src/components/Playground/CoreSwitcher.tsx b/apps/website/src/components/Playground/CoreSwitcher.tsx
new file mode 100644
index 0000000..50596c4
--- /dev/null
+++ b/apps/website/src/components/Playground/CoreSwitcher.tsx
@@ -0,0 +1,34 @@
+import React from "react";
+import Stack from "@mui/material/Stack";
+import FormGroup from "@mui/material/FormGroup";
+import FormControlLabel from "@mui/material/FormControlLabel";
+import Switch from "@mui/material/Switch";
+import IconButton from "@mui/material/IconButton";
+import HelpIcon from "@mui/icons-material/HelpOutline";
+import Tooltip from "@mui/material/Tooltip";
+
+interface CoreSwitcherProps {
+  checked: boolean;
+  onChange: (event: React.ChangeEvent<HTMLInputElement>) => void;
+}
+
+export default function CoreSwitcher({ checked, onChange }: CoreSwitcherProps) {
+  return (
+    <>
+      <Stack direction="row" justifyContent="flex-end">
+        <FormGroup>
+          <FormControlLabel
+            control={<Switch checked={checked} onChange={onChange} />}
+            label="Use Multi-thread"
+            disabled={typeof SharedArrayBuffer !== "function"}
+          />
+        </FormGroup>
+        <Tooltip title="Multi-threaded core is faster, but unstable and not supported by all browsers. Click here for more details.">
+          <IconButton aria-label="help" size="small">
+            <HelpIcon fontSize="small" />
+          </IconButton>
+        </Tooltip>
+      </Stack>
+    </>
+  );
+}
diff --git a/apps/website/src/components/Playground/Editor.tsx b/apps/website/src/components/Playground/Editor.tsx
index b872ef5..7fb059e 100644
--- a/apps/website/src/components/Playground/Editor.tsx
+++ b/apps/website/src/components/Playground/Editor.tsx
@@ -12,29 +12,47 @@ import ListItem from "@mui/material/ListItem";
 import ListItemIcon from "@mui/material/ListItemIcon";
 import ListItemText from "@mui/material/ListItemText";
 import IconButton from "@mui/material/IconButton";
-import MoreVertIcon from "@mui/icons-material/MoreVert";
 import RefreshIcon from "@mui/icons-material/Refresh";
 import UploadFileIcon from "@mui/icons-material/UploadFile";
 import UploadIcon from "@mui/icons-material/Upload";
+import InsertDriveFileIcon from "@mui/icons-material/InsertDriveFile";
+import CreateNewFolderIcon from "@mui/icons-material/CreateNewFolder";
 import Tooltip from "@mui/material/Tooltip";
-import Menu from "@mui/material/Menu";
-import MenuItem from "@mui/material/MenuItem";
+import Paper from "@mui/material/Paper";
 import { useColorMode } from "@docusaurus/theme-common";
 import { FFmpeg } from "@ffmpeg/ffmpeg";
 import { fetchFile } from "@ffmpeg/util";
+import { downloadFile } from "@site/src/util";
 import AceEditor from "react-ace";
-import styles from "./styles.module.css";
 import { getFFmpeg } from "./ffmpeg";
 import { SAMPLE_FILES } from "./const";
 import LinearProgressWithLabel from "./LinearProgressWithLabel";
+import MoreButton from "./MoreButton";
 import "ace-builds/src-noconflict/mode-json";
 import "ace-builds/src-noconflict/mode-javascript";
 import "ace-builds/src-noconflict/mode-text";
 import "ace-builds/src-noconflict/theme-dracula";
 import "ace-builds/src-noconflict/theme-github";
+import ListItemButton from "@mui/material/ListItemButton";
+import Modal from "@mui/material/Modal";
+import TextField from "@mui/material/TextField";
 
 const defaultArgs = JSON.stringify(["-i", "video.avi", "video.mp4"], null, 2);
-const options = ["Download", "Download as Text File", "Delete"];
+const options = [
+  { text: "Download", key: "download" },
+  { text: "Download as Text File", key: "download-text" },
+  { text: "Delete", key: "delete" },
+];
+
+const modalStyle = {
+  position: "absolute" as "absolute",
+  top: "50%",
+  left: "50%",
+  transform: "translate(-50%, -50%)",
+  width: 400,
+  bgcolor: "background.paper",
+  p: 4,
+};
 
 const genFFmpegText = (args: string) => {
   let data: any = [];
@@ -54,33 +72,42 @@ export default function Editor() {
   const [logs, setLogs] = useState<string[]>([]);
   const [output, setOutput] = useState<Ace.Editor>();
   const [path, setPath] = useState<string>("/");
-  const [nodes, setNodes] = useState<string[]>([]);
-  const [progress, setProgress] = useState<number>(-1);
+  const [nodes, setNodes] = useState([]);
+  const [progress, setProgress] = useState<number>(0);
+  const [open, setOpen] = useState(false);
+  const [time, setTime] = useState(0);
+  const [folderName, setFolderName] = useState("");
+  const handleModalOpen = () => setOpen(true);
+  const handleModalClose = () => setOpen(false);
   const { colorMode } = useColorMode();
+
   const theme = colorMode === "dark" ? "github" : "dracula";
 
   const scrollToEnd = () => {
     output && output.renderer.scrollToLine(Number.POSITIVE_INFINITY);
   };
 
-  const loadSamples = async () => {
+  const refreshDir = async (curPath: string) => {
     const ffmpeg = getFFmpeg();
-    Object.keys(SAMPLE_FILES).forEach(async (name) => {
-      await ffmpeg.writeFile(name, await fetchFile(SAMPLE_FILES[name]));
-    });
-    // Somehow we need to wait a little bit before reading the new nodes.
-    setTimeout(async () => {
-      setNodes(await ffmpeg.listDir(path));
-    }, 500);
+    if (ffmpeg.loaded) {
+      setNodes(
+        (await ffmpeg.listDir(curPath)).filter(({ name }) => name !== ".")
+      );
+    }
   };
 
-  const refreshDir = async () => {
-    setNodes(await getFFmpeg().listDir(path));
+  const loadSamples = async () => {
+    const ffmpeg = getFFmpeg();
+    for (const name of Object.keys(SAMPLE_FILES)) {
+      await ffmpeg.writeFile(name, await fetchFile(SAMPLE_FILES[name]));
+    }
+    refreshDir(path);
   };
 
   const exec = async () => {
     const ffmpeg = getFFmpeg();
-    setProgress(-1);
+    setProgress(0);
+    setTime(0);
     const logListener = ({ message }) => {
       setLogs((_logs) => [..._logs, message]);
       scrollToEnd();
@@ -90,157 +117,271 @@ export default function Editor() {
     };
     ffmpeg.on(FFmpeg.LOG, logListener);
     ffmpeg.on(FFmpeg.PROGRESS, progListener);
+    const start = performance.now();
     await ffmpeg.exec(JSON.parse(args));
+    setTime(performance.now() - start);
     ffmpeg.removeListener(FFmpeg.LOG, logListener);
     ffmpeg.removeListener(FFmpeg.PROGRESS, progListener);
-    setNodes(await ffmpeg.listDir(path));
+    refreshDir(path);
+  };
+
+  const cd = (name: string) => async () => {
+    let nextPath = path;
+    if (path === "/") {
+      if (name !== "..") nextPath = `/${name}`;
+    } else if (name === "..") {
+      const cols = path.split("/");
+      cols.pop();
+      nextPath = cols.length === 1 ? "/" : cols.join("/");
+    } else {
+      nextPath = `${path}/${name}`;
+    }
+    setPath(nextPath);
+    refreshDir(nextPath);
+  };
+
+  const handleFileUpload =
+    (isText: boolean = false) =>
+    async ({ target: { files } }: React.ChangeEvent<HTMLInputElement>) => {
+      const ffmpeg = getFFmpeg();
+      for (let i = 0; i < files.length; i++) {
+        const file = files[i];
+        let data: Uint8Array | string = await fetchFile(file);
+        if (isText) data = new TextDecoder().decode(data);
+        await ffmpeg.writeFile(`${path}/${file.name}`, data);
+      }
+      refreshDir(path);
+    };
+
+  const handleItemClick = (name: string) => async (option: string) => {
+    const ffmpeg = getFFmpeg();
+    const fullPath = `${path}/${name}`;
+    switch (option) {
+      case "download":
+        downloadFile(
+          name,
+          ((await ffmpeg.readFile(fullPath, "binary")) as Uint8Array).buffer
+        );
+        break;
+      case "download-text":
+        downloadFile(name, await ffmpeg.readFile(fullPath, "utf8"));
+        break;
+      case "delete":
+        await ffmpeg.deleteFile(fullPath);
+        refreshDir(path);
+        break;
+      default:
+        break;
+    }
+  };
+
+  const handleFolderCreate = async () => {
+    if (folderName !== "") {
+      await getFFmpeg().createDir(`${path}/${folderName}`);
+    }
+    refreshDir(path);
+    handleModalClose();
   };
 
   useEffect(() => {
-    const ffmpeg = getFFmpeg();
-    ffmpeg.listDir(path).then((nodes) => {
-      setNodes(nodes);
-    });
+    refreshDir(path);
   }, []);
 
   return (
     <Box sx={{ flexGrow: 1 }}>
-      <Grid
-        container
-        spacing={{ xs: 2, md: 3 }}
-        columns={{ xs: 4, sm: 8, md: 12 }}
-      >
+      <Grid container spacing={{ xs: 1 }} columns={{ xs: 4, md: 12 }}>
         <Grid item xs={4}>
-          <Stack direction="row" className={styles.fsTitle}>
-            <Typography>File System:</Typography>
-            <Box>
-              <Tooltip title="Upload a media file">
-                <IconButton onClick={() => {}} aria-label="upload-media-file">
-                  <UploadFileIcon />
-                </IconButton>
-              </Tooltip>
-              <Tooltip title="Upload a text file">
-                <IconButton onClick={() => {}} aria-label="upload-text">
-                  <UploadIcon />
-                </IconButton>
-              </Tooltip>
-              <Tooltip title="Refresh directory">
-                <IconButton onClick={refreshDir} aria-label="fresh">
-                  <RefreshIcon />
-                </IconButton>
-              </Tooltip>
-            </Box>
-          </Stack>
-          <Typography>{`${path}`}</Typography>
-          <List dense={true}>
-            {nodes.map((node, index) => (
-              <ListItem
-                key={index}
-                secondaryAction={
-                  <>
-                    <IconButton
-                      aria-label="more"
-                      id="long-button"
-                      aria-haspopup="true"
-                      edge="end"
-                    >
-                      <MoreVertIcon />
-                    </IconButton>
-                    <Menu
-                      id="long-menu"
-                      MenuListProps={{
-                        "aria-labelledby": "long-button",
-                      }}
-                      PaperProps={{
-                        style: {
-                          width: "20ch",
-                        },
-                      }}
-                    >
-                      {options.map((option) => (
-                        <MenuItem key={option} selected={option === "Download"}>
-                          {option}
-                        </MenuItem>
-                      ))}
-                    </Menu>
-                  </>
-                }
-              >
-                <ListItemIcon>
-                  <FolderIcon />
-                </ListItemIcon>
-                <ListItemText primary={node} />
-              </ListItem>
-            ))}
-          </List>
+          <Paper variant="outlined" style={{ padding: 8, height: "100%" }}>
+            <Stack justifyContent="space-between" style={{ height: "100%" }}>
+              <>
+                <Stack
+                  direction="row"
+                  justifyContent="space-between"
+                  alignItems="center"
+                >
+                  <Typography>File System:</Typography>
+                  <Box>
+                    <Tooltip title="Upload a media file">
+                      <IconButton
+                        aria-label="upload-media-file"
+                        component="label"
+                        size="small"
+                      >
+                        <input
+                          hidden
+                          multiple
+                          type="file"
+                          onChange={handleFileUpload(false)}
+                        />
+                        <UploadFileIcon fontSize="small" />
+                      </IconButton>
+                    </Tooltip>
+                    <Tooltip title="Upload a text file">
+                      <IconButton
+                        onClick={() => {}}
+                        aria-label="upload-text"
+                        component="label"
+                        size="small"
+                      >
+                        <input
+                          hidden
+                          multiple
+                          type="file"
+                          onChange={handleFileUpload(true)}
+                        />
+                        <UploadIcon fontSize="small" />
+                      </IconButton>
+                    </Tooltip>
+                    <Tooltip title="Create a new folder">
+                      <IconButton
+                        onClick={() => {
+                          setFolderName("");
+                          handleModalOpen();
+                        }}
+                        aria-label="create-a-new-folder"
+                        size="small"
+                      >
+                        <CreateNewFolderIcon />
+                      </IconButton>
+                    </Tooltip>
+                    <Tooltip title="Refresh directory">
+                      <IconButton
+                        onClick={() => refreshDir(path)}
+                        aria-label="fresh"
+                        size="small"
+                      >
+                        <RefreshIcon fontSize="small" />
+                      </IconButton>
+                    </Tooltip>
+                  </Box>
+                </Stack>
+                <Typography>{`Path: ${path}`}</Typography>
+                <List style={{ height: 480, overflowX: "auto" }}>
+                  {nodes.map(({ name, isDir }, index) =>
+                    isDir ? (
+                      <ListItemButton key={index} onClick={cd(name)}>
+                        <ListItemIcon>
+                          <FolderIcon />
+                        </ListItemIcon>
+                        <ListItemText primary={name} />
+                      </ListItemButton>
+                    ) : (
+                      <ListItem
+                        key={index}
+                        secondaryAction={
+                          <MoreButton
+                            options={options}
+                            onItemClick={handleItemClick(name)}
+                          />
+                        }
+                      >
+                        <ListItemIcon>
+                          <InsertDriveFileIcon />
+                        </ListItemIcon>
+                        <ListItemText primary={name} />
+                      </ListItem>
+                    )
+                  )}
+                </List>
+              </>
+              <Button onClick={loadSamples}>Load Sample Files</Button>
+            </Stack>
+          </Paper>
         </Grid>
         <Grid item xs={8}>
-          <Stack spacing={1}>
-            <Box>
-              <Typography>Edit JSON below to update command:</Typography>
+          <Paper variant="outlined" style={{ padding: 8, height: "100%" }}>
+            <Stack spacing={1}>
+              <Stack>
+                <Typography>Edit JSON below to update command:</Typography>
+                <AceEditor
+                  mode="json"
+                  theme={theme}
+                  name="input-args"
+                  fontSize={16}
+                  showPrintMargin={true}
+                  showGutter={true}
+                  width="100%"
+                  minLines={8}
+                  maxLines={8}
+                  highlightActiveLine={true}
+                  value={args}
+                  onChange={(value) => setArgs(value)}
+                  setOptions={{ tabSize: 2 }}
+                />
+              </Stack>
               <AceEditor
-                mode="json"
+                mode="javascript"
                 theme={theme}
-                name="input-args"
+                name="ffmpeg.wasm"
+                fontSize={16}
+                showGutter={false}
+                width="100%"
+                minLines={6}
+                maxLines={6}
+                readOnly
+                highlightActiveLine={false}
+                value={genFFmpegText(args)}
+                setOptions={{ tabSize: 2 }}
+              />
+              <Typography>Console Output:</Typography>
+              <AceEditor
+                mode="text"
+                theme={theme}
+                name="console"
                 fontSize={16}
-                showPrintMargin={true}
-                showGutter={true}
                 width="100%"
                 minLines={8}
                 maxLines={8}
-                highlightActiveLine={true}
-                value={args}
-                onChange={(value) => setArgs(value)}
+                readOnly
+                showPrintMargin={true}
+                highlightActiveLine={false}
+                value={logs.join("\n")}
                 setOptions={{ tabSize: 2 }}
+                onLoad={(editor) => setOutput(editor)}
               />
-            </Box>
-            <AceEditor
-              mode="javascript"
-              theme={theme}
-              name="ffmpeg.wasm"
-              fontSize={16}
-              showGutter={false}
-              width="100%"
-              minLines={6}
-              maxLines={6}
-              readOnly
-              highlightActiveLine={false}
-              value={genFFmpegText(args)}
-              setOptions={{ tabSize: 2 }}
-            />
-            <Stack direction="row" spacing={2} className={styles.alignRight}>
-              <Button onClick={loadSamples}>Load Sample Files</Button>
-              <Button variant="contained" onClick={exec}>
-                Run
-              </Button>
+              <Typography>Transcoding Progress:</Typography>
+              <LinearProgressWithLabel value={progress} />
+              <Stack direction="row" spacing={2} justifyContent="space-between">
+                <Typography>
+                  {time === 0
+                    ? ""
+                    : `Time Elapsed: ${(time / 1000).toFixed(2)} s`}
+                </Typography>
+                <Button variant="contained" onClick={exec}>
+                  Run
+                </Button>
+              </Stack>
             </Stack>
-            {progress === -1 ? (
-              <></>
-            ) : (
-              <>
-                <Typography>Transcoding Progress:</Typography>
-                <LinearProgressWithLabel value={progress} />
-              </>
-            )}
-            <AceEditor
-              placeholder="ffmpeg console output"
-              mode="text"
-              theme={theme}
-              name="console"
-              fontSize={16}
-              width="100%"
-              minLines={8}
-              maxLines={8}
-              readOnly
-              showPrintMargin={true}
-              highlightActiveLine={false}
-              value={logs.join("\n")}
-              setOptions={{ tabSize: 2 }}
-              onLoad={(editor) => setOutput(editor)}
-            />
-          </Stack>
+          </Paper>
         </Grid>
       </Grid>
+      <Modal
+        open={open}
+        onClose={handleModalClose}
+        aria-labelledby="new-folder-name"
+        aria-describedby="new-folder-name-description"
+      >
+        <Box sx={modalStyle}>
+          <Stack spacing={4}>
+            <Typography id="modal-modal-title" variant="h6" component="h2">
+              Folder Name:
+            </Typography>
+            <TextField
+              id="outlined-basic"
+              label="my-folder"
+              variant="outlined"
+              value={folderName}
+              onChange={(event) => setFolderName(event.target.value)}
+            />
+            <Stack direction="row" justifyContent="flex-end">
+              <Button onClick={handleModalClose}>Cancel</Button>
+              <Button variant="contained" onClick={handleFolderCreate}>
+                Create
+              </Button>
+            </Stack>
+          </Stack>
+        </Box>
+      </Modal>
     </Box>
   );
 }
diff --git a/apps/website/src/components/Playground/MoreButton.tsx b/apps/website/src/components/Playground/MoreButton.tsx
new file mode 100644
index 0000000..2f802c3
--- /dev/null
+++ b/apps/website/src/components/Playground/MoreButton.tsx
@@ -0,0 +1,69 @@
+import * as React from "react";
+import IconButton from "@mui/material/IconButton";
+import Menu from "@mui/material/Menu";
+import MenuItem from "@mui/material/MenuItem";
+import MoreVertIcon from "@mui/icons-material/MoreVert";
+
+const ITEM_HEIGHT = 48;
+
+interface Option {
+  key: string;
+  text: string;
+}
+
+interface MoreButtonProps {
+  options: Option[];
+  onItemClick: (option: string) => any;
+}
+
+export default function MoreButton({ options, onItemClick }: MoreButtonProps) {
+  const [anchorEl, setAnchorEl] = React.useState<null | HTMLElement>(null);
+  const open = Boolean(anchorEl);
+  const handleClick = (event: React.MouseEvent<HTMLElement>) => {
+    setAnchorEl(event.currentTarget);
+  };
+  const handleClose = () => {
+    setAnchorEl(null);
+  };
+
+  const handleItemClick = (option: string) => () => {
+    onItemClick(option);
+    setAnchorEl(null);
+  };
+
+  return (
+    <div>
+      <IconButton
+        aria-label="more"
+        id="more-button"
+        aria-controls={open ? "menu" : undefined}
+        aria-expanded={open ? "true" : undefined}
+        aria-haspopup="true"
+        onClick={handleClick}
+      >
+        <MoreVertIcon />
+      </IconButton>
+      <Menu
+        id="menu"
+        MenuListProps={{
+          "aria-labelledby": "more-button",
+        }}
+        anchorEl={anchorEl}
+        open={open}
+        onClose={handleClose}
+        PaperProps={{
+          style: {
+            maxHeight: ITEM_HEIGHT * 4.5,
+            width: "20ch",
+          },
+        }}
+      >
+        {options.map(({ text, key }) => (
+          <MenuItem key={key} onClick={handleItemClick(key)}>
+            {text}
+          </MenuItem>
+        ))}
+      </Menu>
+    </div>
+  );
+}
diff --git a/apps/website/src/components/Playground/const.ts b/apps/website/src/components/Playground/const.ts
index 907dd87..a4f1802 100644
--- a/apps/website/src/components/Playground/const.ts
+++ b/apps/website/src/components/Playground/const.ts
@@ -1,9 +1,14 @@
+export const CORE_VERSION = "0.12.0-alpha.2";
+
+export const CORE_URL = `https://unpkg.com/@ffmpeg/core@${CORE_VERSION}/dist/umd/ffmpeg-core.js`;
+export const CORE_MT_URL = `https://unpkg.com/@ffmpeg/core-mt@${CORE_VERSION}/dist/umd/ffmpeg-core.js`;
+
 export const CORE_SIZE = {
-  "https://unpkg.com/@ffmpeg/core@0.12.0-alpha.2/dist/umd/ffmpeg-core.js": 111646,
-  "https://unpkg.com/@ffmpeg/core@0.12.0-alpha.2/dist/umd/ffmpeg-core.wasm": 31967534,
-  "https://unpkg.com/@ffmpeg/core-mt@0.12.0-alpha.2/dist/umd/ffmpeg-core.js": 130002,
-  "https://unpkg.com/@ffmpeg/core-mt@0.12.0-alpha.2/dist/umd/ffmpeg-core.wasm": 32441947,
-  "https://unpkg.com/@ffmpeg/core-mt@0.12.0-alpha.2/dist/umd/ffmpeg-core.worker.js": 2978,
+  [`https://unpkg.com/@ffmpeg/core@${CORE_VERSION}/dist/umd/ffmpeg-core.js`]: 111646,
+  [`https://unpkg.com/@ffmpeg/core@${CORE_VERSION}/dist/umd/ffmpeg-core.wasm`]: 31967534,
+  [`https://unpkg.com/@ffmpeg/core-mt@${CORE_VERSION}/dist/umd/ffmpeg-core.js`]: 130002,
+  [`https://unpkg.com/@ffmpeg/core-mt@${CORE_VERSION}/dist/umd/ffmpeg-core.wasm`]: 32441947,
+  [`https://unpkg.com/@ffmpeg/core-mt@${CORE_VERSION}/dist/umd/ffmpeg-core.worker.js`]: 2978,
 };
 
 export const SAMPLE_FILES = {
diff --git a/apps/website/src/components/Playground/index.tsx b/apps/website/src/components/Playground/index.tsx
index dd66d87..82626c5 100644
--- a/apps/website/src/components/Playground/index.tsx
+++ b/apps/website/src/components/Playground/index.tsx
@@ -1,10 +1,12 @@
 import * as React from "react";
 import { FFmpeg } from "@ffmpeg/ffmpeg";
+import Stack from "@mui/material/Stack";
 import MuiThemeProvider from "@site/src/components/MuiThemeProvider";
-import CoreSelector from "./CoreSelector";
 import CoreDownloader from "./CoreDownloader";
 import Editor from "./Editor";
 import { getFFmpeg } from "./ffmpeg";
+import { CORE_URL, CORE_MT_URL } from "./const";
+import CoreSwitcher from "./CoreSwitcher";
 
 enum State {
   NOT_LOADED,
@@ -13,12 +15,12 @@ enum State {
 }
 
 export default function Playground() {
-  const { useState } = React;
+  const { useState, useEffect } = React;
   const [state, setState] = useState(State.LOADED);
-  const [option, setOption] = useState("core");
+  const [isCoreMT, setIsCoreMT] = useState(false);
   const [url, setURL] = useState("");
   const [received, setReceived] = useState(0);
-  const load = async () => {
+  const load = async (mt: boolean = false) => {
     setState(State.LOADING);
     const ffmpeg = getFFmpeg();
     ffmpeg.terminate();
@@ -26,29 +28,38 @@ export default function Playground() {
       setURL(_url as string);
       setReceived(_received);
     });
-    await ffmpeg.load();
+    await ffmpeg.load({
+      coreURL: mt ? CORE_MT_URL : CORE_URL,
+      thread: mt,
+    });
     setState(State.LOADED);
   };
 
+  useEffect(() => {
+    load(isCoreMT);
+  }, []);
+
   return (
     <MuiThemeProvider>
-      {(() => {
-        switch (state) {
-          case State.LOADING:
-            return <CoreDownloader url={url} received={received} />;
-          case State.LOADED:
-            return <Editor />;
-          default:
-            return <></>;
-        }
-      })()}
-      <CoreSelector
-        option={option}
-        onChange={(event) => {
-          setOption((event.target as HTMLInputElement).value);
-        }}
-        onSubmit={load}
-      />
+      <Stack spacing={4}>
+        <CoreSwitcher
+          checked={isCoreMT}
+          onChange={(evt) => {
+            setIsCoreMT(evt.target.checked);
+            load(evt.target.checked);
+          }}
+        />
+        {(() => {
+          switch (state) {
+            case State.LOADING:
+              return <CoreDownloader url={url} received={received} />;
+            case State.LOADED:
+              return <Editor />;
+            default:
+              return <></>;
+          }
+        })()}
+      </Stack>
     </MuiThemeProvider>
   );
 }
diff --git a/apps/website/src/components/Playground/styles.module.css b/apps/website/src/components/Playground/styles.module.css
index b6a7e1e..e69de29 100644
--- a/apps/website/src/components/Playground/styles.module.css
+++ b/apps/website/src/components/Playground/styles.module.css
@@ -1,13 +0,0 @@
-.margin {
-  margin-bottom: 32px;
-}
-
-.alignRight {
-  display: flex;
-  justify-content: flex-end;
-}
-
-.fsTitle {
-  align-items: center;
-  justify-content: space-between;
-}
diff --git a/apps/website/src/util.ts b/apps/website/src/util.ts
new file mode 100644
index 0000000..8a65af5
--- /dev/null
+++ b/apps/website/src/util.ts
@@ -0,0 +1,9 @@
+export const downloadFile = (name: string, data: ArrayBuffer | string) => {
+  const a = document.createElement("a");
+  const blob = new Blob([data]);
+  const url = window.URL.createObjectURL(blob);
+  a.href = url;
+  a.download = name;
+  a.click();
+  window.URL.revokeObjectURL(url);
+};
diff --git a/packages/ffmpeg/src/classes.ts b/packages/ffmpeg/src/classes.ts
index d04fe98..e14df3a 100644
--- a/packages/ffmpeg/src/classes.ts
+++ b/packages/ffmpeg/src/classes.ts
@@ -4,7 +4,7 @@ import {
   CallbackData,
   Callbacks,
   DownloadProgressEvent,
-  FFFSPaths,
+  FSNode,
   FFMessageEventCallback,
   FFMessageLoadConfig,
   OK,
@@ -94,6 +94,8 @@ export class FFmpeg extends EventEmitter {
   #resolves: Callbacks = {};
   #rejects: Callbacks = {};
 
+  public loaded = false;
+
   constructor() {
     super();
   }
@@ -108,6 +110,9 @@ export class FFmpeg extends EventEmitter {
       }: FFMessageEventCallback) => {
         switch (type) {
           case FFMessageType.LOAD:
+            this.loaded = true;
+            this.#resolves[id](data);
+            break;
           case FFMessageType.EXEC:
           case FFMessageType.WRITE_FILE:
           case FFMessageType.READ_FILE:
@@ -227,6 +232,7 @@ export class FFmpeg extends EventEmitter {
     if (this.#worker) {
       this.#worker.terminate();
       this.#worker = null;
+      this.loaded = false;
     }
   };
 
@@ -323,11 +329,11 @@ export class FFmpeg extends EventEmitter {
    *
    * @category File System
    */
-  public listDir = (path: string): Promise<FFFSPaths> =>
+  public listDir = (path: string): Promise<FSNode[]> =>
     this.#send({
       type: FFMessageType.LIST_DIR,
       data: { path },
-    }) as Promise<FFFSPaths>;
+    }) as Promise<FSNode[]>;
 
   /**
    * Delete an empty directory.
diff --git a/packages/ffmpeg/src/types.ts b/packages/ffmpeg/src/types.ts
index 66f6927..c2f7449 100644
--- a/packages/ffmpeg/src/types.ts
+++ b/packages/ffmpeg/src/types.ts
@@ -1,5 +1,4 @@
 export type FFFSPath = string;
-export type FFFSPaths = FFFSPath[];
 
 /**
  * ffmpeg-core loading configuration.
@@ -136,6 +135,11 @@ export type FileData = Uint8Array | string;
 export type IsFirst = boolean;
 export type OK = boolean;
 
+export interface FSNode {
+  name: string;
+  isDir: boolean;
+}
+
 export type CallbackData =
   | FileData
   | ExitCode
@@ -146,7 +150,7 @@ export type CallbackData =
   | IsFirst
   | OK
   | Error
-  | FFFSPaths
+  | FSNode[]
   | undefined;
 
 export interface Callbacks {
diff --git a/packages/ffmpeg/src/worker.ts b/packages/ffmpeg/src/worker.ts
index 1f38e50..14ee56a 100644
--- a/packages/ffmpeg/src/worker.ts
+++ b/packages/ffmpeg/src/worker.ts
@@ -18,7 +18,7 @@ import type {
   IsFirst,
   OK,
   ExitCode,
-  FFFSPaths,
+  FSNode,
   FileData,
 } from "./types";
 import { toBlobURL } from "./utils";
@@ -118,8 +118,15 @@ const createDir = ({ path }: FFMessageCreateDirData): OK => {
   return true;
 };
 
-const listDir = ({ path }: FFMessageListDirData): FFFSPaths => {
-  return ffmpeg.FS.readdir(path);
+const listDir = ({ path }: FFMessageListDirData): FSNode[] => {
+  const names = ffmpeg.FS.readdir(path);
+  const nodes: FSNode[] = [];
+  for (const name of names) {
+    const stat = ffmpeg.FS.stat(`${path}/${name}`);
+    const isDir = ffmpeg.FS.isDir(stat.mode);
+    nodes.push({ name, isDir });
+  }
+  return nodes;
 };
 
 // TODO: check if deletion works.