fix(next/image): prefer sharp defaults, use mozjpeg for JPEG

- Default concurrency detection is better than os.cpus() as it
inspects things like CPU set/affinity as well as the memory
allocator.

- Prevents use of archaic chroma subsampling for AVIF output.
This should improve the quality of red/orange edges and slightly
reduce file size as AV1 chroma-from-luma prediction works better.

- There's no need to set sequentialRead as sharp now manages this
for each input image and the operations in the pipeline.

- Defaults JPEG output to use mozjpeg features such as trellis
quantisation as these produce smaller file sizes. This should
produce consistent output with squoosh at the same quality.

packages/next/src/server/image-optimizer.ts

@@ -1,6 +1,5 @@
 import { createHash } from 'crypto'
 import { promises } from 'fs'
-import { cpus } from 'os'
 import type { IncomingMessage, ServerResponse } from 'http'
 import { mediaType } from 'next/dist/compiled/@hapi/accept'
 import contentDisposition from 'next/dist/compiled/content-disposition'
@@ -47,13 +46,6 @@ function getSharp() {
   }
   try {
     _sharp = require('sharp')
-    if (_sharp && _sharp.concurrency() > 1) {
-      // Reducing concurrency should reduce the memory usage too.
-      // We more aggressively reduce in dev but also reduce in prod.
-      // https://sharp.pixelplumbing.com/api-utility#concurrency
-      const divisor = process.env.NODE_ENV === 'development' ? 4 : 2
-      _sharp.concurrency(Math.floor(Math.max(cpus().length / divisor, 1)))
-    }
   } catch (e: unknown) {
     if (isError(e) && e.code === 'MODULE_NOT_FOUND') {
       throw new Error(
@@ -444,9 +436,7 @@ export async function optimizeImage({
   nextConfigOutput?: 'standalone' | 'export'
 }): Promise<Buffer> {
   const sharp = getSharp()
-  const transformer = sharp(buffer, { sequentialRead: true })
-    .timeout({ seconds: 7 })
-    .rotate()
+  const transformer = sharp(buffer).timeout({ seconds: 7 }).rotate()
 
   if (height) {
     transformer.resize(width, height)
@@ -460,14 +450,13 @@ export async function optimizeImage({
     const avifQuality = quality - 15
     transformer.avif({
       quality: Math.max(avifQuality, 0),
-      chromaSubsampling: '4:2:0', // same as webp
     })
   } else if (contentType === WEBP) {
     transformer.webp({ quality })
   } else if (contentType === PNG) {
     transformer.png({ quality })
   } else if (contentType === JPEG) {
-    transformer.jpeg({ quality, progressive: true })
+    transformer.jpeg({ quality, mozjpeg: true })
   }
 
   const optimizedBuffer = await transformer.toBuffer()