Add transcode module

packages/ditto/utils/transcode.test.ts

@@ -0,0 +1,8 @@
+import { transcodeVideoStream } from './transcode.ts';
+
+Deno.test('transcodeVideoStream', async () => {
+  await using file = await Deno.open(new URL('./buckbunny.mp4', import.meta.url));
+  const output = await transcodeVideoStream(file.readable);
+
+  await Deno.writeFile(new URL('./buckbunny-transcoded.mp4', import.meta.url), output);
+});

packages/ditto/utils/transcode.ts

@@ -0,0 +1,62 @@
+export async function transcodeVideoStream(
+  inputStream: ReadableStream<Uint8Array>,
+): Promise<ReadableStream<Uint8Array>> {
+  const command = new Deno.Command('ffmpeg', {
+    args: [
+      '-i',
+      'pipe:0', // Read input from stdin
+      '-c:v',
+      'libx264', // Convert to H.264
+      '-preset',
+      'veryfast', // Encoding speed
+      '-loglevel',
+      'fatal', // Suppress logs
+      '-crf',
+      '23', // Compression level (lower = better quality)
+      '-c:a',
+      'aac', // Convert to AAC audio
+      '-b:a',
+      '128k', // Audio bitrate
+      '-movflags',
+      'frag_keyframe+empty_moov', // Ensures MP4 streaming compatibility
+      '-f',
+      'mp4', // Force MP4 format
+      'pipe:1', // Output to stdout
+    ],
+    stdin: 'piped',
+    stdout: 'piped',
+    stderr: 'piped',
+  });
+
+  // Spawn the FFmpeg process
+  const process = command.spawn();
+
+  // Capture stderr for debugging
+  const stderrPromise = new Response(process.stderr).text().then((text) => {
+    if (text.trim()) console.error('FFmpeg stderr:', text);
+  });
+
+  // Pipe the input stream into FFmpeg stdin and ensure completion
+  const writer = process.stdin.getWriter();
+  const reader = inputStream.getReader();
+
+  async function pumpInput() {
+    try {
+      while (true) {
+        const { done, value } = await reader.read();
+        if (done) break;
+        await writer.write(value);
+      }
+    } finally {
+      writer.close(); // Close stdin to signal FFmpeg that input is done
+    }
+  }
+
+  // Start pumping input asynchronously
+  pumpInput();
+
+  // Ensure stderr logs are captured
+  stderrPromise.catch(console.error);
+
+  return process.stdout;
+}