Record the JSPI core's size

apps/website/docs/getting-started/usage.md

@@ -574,9 +574,9 @@ Asyncify, which rewrites the wasm code. The JSPI core does the same job with
 [JavaScript Promise Integration](https://github.com/WebAssembly/js-promise-integration),
 a feature of the browser and Node.js. It runs the same FFmpeg and the same
 `src/pthread-fiber` scheduler, so it needs no `SharedArrayBuffer`. Its wasm
-file is about 19% smaller than the default core's (32.4 MB against 40.1 MB,
-before compression), and the CI benchmark cases ran faster and used less
-memory.
+file is about {Math.round((1 - coreSizes["core-jspi"]["ffmpeg-core.wasm"] / coreSizes.core["ffmpeg-core.wasm"]) * 100)}% smaller than the default core's
+({(coreSizes["core-jspi"]["ffmpeg-core.wasm"] / 1e6).toFixed(1)} MB against {(coreSizes.core["ffmpeg-core.wasm"] / 1e6).toFixed(1)} MB, before compression), and the CI
+benchmark cases ran faster and used less memory.
 
 It needs a runtime with JSPI: Chrome 137 or later, Firefox 153 or later,
 Safari 27 or later, or Node.js 24 or later (tested on 24.21.0, and an older
@@ -626,7 +626,7 @@ return a Promise instead of a number, so `await` them.
 - It has only been tested on short clips in CI, the wrapper test suites and
   FFmpeg's FATE tests. It has had no long-running or large-file testing, and
   no memory-leak testing over many commands.
-- It is not on the Playground, and its size is not in `core-sizes.json`.
+- It is not on the Playground.
 
 ## Node.js
 

apps/website/src/data/core-sizes.json

@@ -7,5 +7,9 @@
   "core-mt": {
     "ffmpeg-core.js": 113289,
     "ffmpeg-core.wasm": 32778819
+  },
+  "core-jspi": {
+    "ffmpeg-core.js": 97901,
+    "ffmpeg-core.wasm": 32412275
   }
 }

scripts/update-core-sizes.mjs

@@ -4,7 +4,7 @@
 //
 // Usage: node scripts/update-core-sizes.mjs <version> [--run <run-id>]
 // Default reads the published packages from the jsDelivr data API. --run
-// reads the ffmpeg-core and ffmpeg-core-mt artifacts of a CI run with gh
+// reads the ffmpeg-core, -core-mt and -core-jspi artifacts of a CI run with gh
 // instead, for a release PR whose version is not published yet. The cores
 // are built from the same inputs, so the sizes hold for the tag.
 import { execFileSync } from "node:child_process";
@@ -48,7 +48,7 @@ async function sizesFromJsdelivr(pkg) {
 const sizes = { version };
 const scratch = mkdtempSync(join(tmpdir(), "core-sizes-"));
 try {
-  for (const pkg of ["core", "core-mt"]) {
+  for (const pkg of ["core", "core-mt", "core-jspi"]) {
     sizes[pkg] = flag ? sizesFromRun(pkg, scratch) : await sizesFromJsdelivr(pkg);
   }
 } finally {