feat: support webm format in screencast (#1934)

Modifies the experimental screencast command to support `.webm` in
addition to `.mp4`. Renamed `path` to `filePath` to align with other
tools.

src/telemetry/tool_call_metrics.json

@@ -419,6 +419,11 @@
     "args": [
       {
         "name": "path_length",
+        "argType": "number",
+        "isDeprecated": true
+      },
+      {
+        "name": "file_path_length",
         "argType": "number"
       }
     ]

src/tools/screencast.ts

@@ -9,7 +9,7 @@ import os from 'node:os';
 import path from 'node:path';
 
 import {zod} from '../third_party/index.js';
-import type {ScreenRecorder} from '../third_party/index.js';
+import type {ScreenRecorder, VideoFormat} from '../third_party/index.js';
 import {ensureExtension} from '../utils/files.js';
 
 import {ToolCategory} from './categories.js';
@@ -20,10 +20,11 @@ async function generateTempFilePath(): Promise<string> {
   return path.join(dir, `screencast.mp4`);
 }
 
+const supportedExtensions: Array<`.${string}`> = ['.webm', '.mp4'];
+
 export const startScreencast = definePageTool(args => ({
   name: 'screencast_start',
-  description:
-    'Starts recording a screencast (video) of the selected page in mp4 format.',
+  description: `Starts recording a screencast (video) of the selected page in specified format.`,
   annotations: {
     category: ToolCategory.DEBUGGING,
     readOnlyHint: false,
@@ -31,11 +32,11 @@ export const startScreencast = definePageTool(args => ({
     conditions: ['screencast'],
   },
   schema: {
-    path: zod
+    filePath: zod
       .string()
       .optional()
       .describe(
-        'Output path. Uses mkdtemp to generate a unique path if not provided.',
+        `Output file path (${supportedExtensions.join(',')} are supported). Uses mkdtemp to generate a unique path if not provided.`,
       ),
   },
   handler: async (request, response, context) => {
@@ -46,16 +47,30 @@ export const startScreencast = definePageTool(args => ({
       return;
     }
 
-    const filePath = request.params.path ?? (await generateTempFilePath());
-    const resolvedPath = ensureExtension(path.resolve(filePath), '.mp4');
+    const filePath = request.params.filePath ?? (await generateTempFilePath());
+    let enforcedExtension = '.mp4' as `.${string}`;
+    let format: VideoFormat = 'mp4';
+
+    for (const supportedExtension of supportedExtensions) {
+      if (filePath.endsWith(supportedExtension)) {
+        enforcedExtension = supportedExtension;
+        format = supportedExtension.substring(1) as VideoFormat;
+        break;
+      }
+    }
+
+    const resolvedPath = ensureExtension(
+      path.resolve(filePath),
+      enforcedExtension,
+    ) as `${string}.webm`;
 
     const page = request.page;
 
     let recorder: ScreenRecorder;
     try {
       recorder = await page.pptrPage.screencast({
-        path: resolvedPath as `${string}.mp4`,
-        format: 'mp4' as const,
+        path: resolvedPath,
+        format: format,
         ffmpegPath: args?.experimentalFfmpegPath,
       });
     } catch (err) {

tests/tools/screencast.test.ts

@@ -35,7 +35,7 @@ describe('screencast', () => {
 
         await startScreencast().handler(
           {
-            params: {path: '/tmp/test-recording.mp4'},
+            params: {filePath: '/tmp/test-recording.mp4'},
             page: context.getSelectedMcpPage(),
           },
           response,
@@ -113,7 +113,7 @@ describe('screencast', () => {
         await assert.rejects(
           startScreencast().handler(
             {
-              params: {path: '/tmp/test.mp4'},
+              params: {filePath: '/tmp/test.mp4'},
               page: context.getSelectedMcpPage(),
             },
             response,