web/ffmpeg: define multithreading support outside of web worker context

there's no navigator.maxTouchPoints in web worker context, so previously there was no way to detect whether safari is running on ipad or not

web/src/lib/libav.ts

@@ -5,12 +5,6 @@ import EncodeLibAV from "@imput/libav.js-encode-cli";
 import type { FfprobeData } from "fluent-ffmpeg";
 import type { FFmpegProgressCallback, FFmpegProgressEvent, FFmpegProgressStatus, RenderParams } from "$lib/types/libav";
 
-const ua = navigator.userAgent.toLowerCase();
-const iPhone = ua.includes("iphone os");
-const iPad = !iPhone && ua.includes("mac os") && navigator.maxTouchPoints > 0;
-const iOS = iPhone || iPad;
-const modernIOS = iOS && Number(ua.match(/version\/(\d+)/)?.[1]) >= 18;
-
 export default class LibAVWrapper {
     libav: Promise<LibAVInstance> | null;
     concurrency: number;
@@ -38,7 +32,6 @@ export default class LibAVWrapper {
             this.libav = constructor({
                 ...options,
                 variant: undefined,
-                yesthreads: !iOS || modernIOS,
                 base: '/_libav'
             });
         }

web/src/lib/task-manager/runners/ffmpeg.ts

@@ -1,5 +1,6 @@
 import FFmpegWorker from "$lib/task-manager/workers/ffmpeg?worker";
 
+import { device } from "$lib/device";
 import { killWorker } from "$lib/task-manager/run-worker";
 import { updateWorkerProgress } from "$lib/state/task-manager/current-tasks";
 import { pipelineTaskDone, itemError, queue } from "$lib/state/task-manager/queue";
@@ -34,7 +35,11 @@ export const runFFmpegWorker = async (
             startAttempts++;
             if (startAttempts <= 10) {
                 killWorker(worker, unsubscribe, startCheck);
-                return await runFFmpegWorker(workerId, parentId, files, args, output, variant);
+                return await runFFmpegWorker(
+                    workerId, parentId,
+                    files, args, output,
+                    variant, device.supports.multithreading
+                );
             } else {
                 killWorker(worker, unsubscribe, startCheck);
                 return itemError(parentId, workerId, "queue.worker_didnt_start");

web/src/lib/task-manager/workers/ffmpeg.ts

@@ -1,7 +1,13 @@
 import LibAVWrapper from "$lib/libav";
 import type { FileInfo } from "$lib/types/libav";
 
-const ffmpeg = async (variant: string, files: File[], args: string[], output: FileInfo) => {
+const ffmpeg = async (
+    variant: string,
+    files: File[],
+    args: string[],
+    output: FileInfo,
+    yesthreads: boolean
+) => {
     if (!(files && output && args)) {
         self.postMessage({
             cobaltFFmpegWorker: {
@@ -25,7 +31,7 @@ const ffmpeg = async (variant: string, files: File[], args: string[], output: Fi
         })
     });
 
-    ff.init({ variant });
+    ff.init({ variant, yesthreads });
 
     const error = (code: string) => {
         self.postMessage({
@@ -121,7 +127,7 @@ const ffmpeg = async (variant: string, files: File[], args: string[], output: Fi
 
 self.onmessage = async (event: MessageEvent) => {
     const ed = event.data.cobaltFFmpegWorker;
-    if (ed?.variant && ed?.files && ed?.args && ed?.output) {
-        await ffmpeg(ed.variant, ed.files, ed.args, ed.output);
+    if (ed?.variant && ed?.files && ed?.args && ed?.output && ed?.yesthreads) {
+        await ffmpeg(ed.variant, ed.files, ed.args, ed.output, ed.yesthreads);
     }
 }