Preview compatible fragmented MP4 transfers while saving the verified copy

frontend/direct-stream.test.js

@@ -0,0 +1,12 @@
+const { test } = require('node:test');
+const assert = require('node:assert/strict');
+const { inspectBytes } = require('./direct-stream.js');
+function box(type, payload = Buffer.alloc(0)) { const b = Buffer.alloc(8 + payload.length); b.writeUInt32BE(b.length); b.write(type, 4); payload.copy(b, 8); return b; }
+test('progressive playback only accepts a complete fragmented MP4 initialization', () => {
+  const codec = box('avcC', Buffer.from([1, 0x64, 0, 0x1f]));
+  const fragmented = Buffer.concat([box('ftyp'), box('moov', Buffer.concat([box('mvex'), codec, box('mp4a')]))]);
+  assert.equal(inspectBytes(fragmented), 'video/mp4; codecs="avc1.64001f, mp4a.40.2"');
+  assert.equal(inspectBytes(Buffer.concat([box('ftyp'), box('moov', codec)])), null);
+  assert.equal(inspectBytes(fragmented.subarray(0, fragmented.length - 1)), null);
+  assert.equal(inspectBytes(Buffer.alloc(0)), null);
+});