perf: stream ffmpeg output to response to reduce memory usage and latency

Co-authored-by: soruly <1979746+soruly@users.noreply.github.com>

Author: google-labs-jules[bot]

src/lib/generate-video-preview.ts

@@ -0,0 +1,73 @@
+import child_process from "node:child_process";
+
+const generateVideoPreview = (
+  filePath: string,
+  start: number,
+  end: number,
+  size: string = "m",
+  mute: boolean = false,
+) => {
+  const ffmpeg = child_process.spawn(
+    "ffmpeg",
+    [
+      "-hide_banner",
+      "-loglevel",
+      "error",
+      "-nostats",
+      "-y",
+      "-ss",
+      `${start - 10}`,
+      "-i",
+      filePath,
+      "-ss",
+      "10",
+      "-t",
+      `${end - start}`,
+      mute ? "-an" : "-y",
+      "-map",
+      "0:v:0",
+      "-map",
+      "0:a:0?",
+      "-vf",
+      `scale=${{ l: 640, m: 320, s: 160 }[size]}:-2`,
+      "-c:v",
+      "libx264",
+      "-crf",
+      "25",
+      "-profile:v",
+      "high",
+      "-preset",
+      "veryfast",
+      "-bf",
+      "8",
+      "-r",
+      "24000/1001",
+      "-pix_fmt",
+      "yuv420p",
+      "-c:a",
+      "aac",
+      "-ac",
+      "2",
+      "-b:a",
+      "64k",
+      "-max_muxing_queue_size",
+      "1024",
+      "-movflags",
+      "empty_moov+faststart",
+      "-map_metadata",
+      "-1",
+      "-map_chapters",
+      "-1",
+      "-f",
+      "mp4",
+      "-",
+    ],
+    { timeout: 10000 },
+  );
+  ffmpeg.stderr.on("data", (data) => {
+    console.log(data.toString());
+  });
+  return ffmpeg;
+};
+
+export default generateVideoPreview;

src/video.ts

@@ -1,84 +1,13 @@
 import path from "node:path";
 import fs from "node:fs/promises";
 import crypto from "node:crypto";
-import child_process from "node:child_process";
 import { Buffer } from "node:buffer";
 import sql from "../sql.ts";
 import detectScene from "./lib/detect-scene.ts";
+import generateVideoPreview from "./lib/generate-video-preview.ts";
 
 const { VIDEO_PATH, TRACE_API_SALT, MEDIA_QUEUE = Infinity } = process.env;
 
-const generateVideoPreview = async (filePath, start, end, size = "m", mute = false) =>
-  new Promise((resolve) => {
-    const ffmpeg = child_process.spawn(
-      "ffmpeg",
-      [
-        "-hide_banner",
-        "-loglevel",
-        "error",
-        "-nostats",
-        "-y",
-        "-ss",
-        start - 10,
-        "-i",
-        filePath,
-        "-ss",
-        "10",
-        "-t",
-        end - start,
-        mute ? "-an" : "-y",
-        "-map",
-        "0:v:0",
-        "-map",
-        "0:a:0?",
-        "-vf",
-        `scale=${{ l: 640, m: 320, s: 160 }[size]}:-2`,
-        "-c:v",
-        "libx264",
-        "-crf",
-        "25",
-        "-profile:v",
-        "high",
-        "-preset",
-        "veryfast",
-        "-bf",
-        "8",
-        "-r",
-        "24000/1001",
-        "-pix_fmt",
-        "yuv420p",
-        "-c:a",
-        "aac",
-        "-ac",
-        "2",
-        "-b:a",
-        "64k",
-        "-max_muxing_queue_size",
-        "1024",
-        "-movflags",
-        "empty_moov+faststart",
-        "-map_metadata",
-        "-1",
-        "-map_chapters",
-        "-1",
-        "-f",
-        "mp4",
-        "-",
-      ],
-      { timeout: 10000 },
-    );
-    ffmpeg.stderr.on("data", (data) => {
-      console.log(data.toString());
-    });
-    const chunks = [];
-    ffmpeg.stdout.on("data", (data) => {
-      chunks.push(data);
-    });
-    ffmpeg.on("close", () => {
-      resolve(Buffer.concat(chunks));
-    });
-  });
-
 export default async (req, res) => {
   const [fileId, time, expire, hash] = req.app.locals.sqids.decode(req.params.id);
   const buf = Buffer.from(TRACE_API_SALT);
@@ -137,7 +66,6 @@ export default async (req, res) => {
     }
 
     const muted = "mute" in req.query;
-    const video = await generateVideoPreview(videoFilePath, scene.start, scene.end, size, muted);
 
     res.set("Cache-Control", "max-age=86400");
     res.set("Content-Type", "video/mp4");
@@ -146,10 +74,22 @@ export default async (req, res) => {
     res.set("x-video-end", scene.end);
     res.set("x-video-duration", scene.duration);
     res.set("Access-Control-Expose-Headers", "x-video-start, x-video-end, x-video-duration");
-    res.send(video);
+
+    const ffmpeg = generateVideoPreview(videoFilePath, scene.start, scene.end, size, muted);
+
+    ffmpeg.stdout.pipe(res);
+
+    await new Promise<void>((resolve) => {
+      ffmpeg.on("close", () => resolve());
+      ffmpeg.on("error", (err) => {
+        console.log(err);
+        res.end();
+        resolve();
+      });
+    });
   } catch (e) {
     console.log(e);
-    res.status(500).send("Internal Server Error");
+    if (!res.headersSent) res.status(500).send("Internal Server Error");
   }
   req.app.locals.mediaQueue--;
 };