web/ffmpeg: accept and return blob, proper types & extensions, clean up

pnpm-lock.yaml

@@ -109,6 +109,9 @@ importers:
       '@vitejs/plugin-basic-ssl':
         specifier: ^1.1.0
         version: 1.1.0(vite@5.3.5(@types/node@20.14.14))
+      mime:
+        specifier: ^4.0.4
+        version: 4.0.4
       sveltekit-i18n:
         specifier: ^2.4.2
         version: 2.4.2(svelte@4.2.18)
@@ -1591,6 +1594,11 @@ packages:
     engines: {node: '>=4'}
     hasBin: true
 
+  mime@4.0.4:
+    resolution: {integrity: sha512-v8yqInVjhXyqP6+Kw4fV3ZzeMRqEW6FotRsKXjRS5VMTNIuXsdRoAvklpoRgSqXm6o9VNH4/C0mgedko9DdLsQ==}
+    engines: {node: '>=16'}
+    hasBin: true
+
   mimic-fn@2.1.0:
     resolution: {integrity: sha512-OqbOk5oEQeAZ8WXWydlu9HJjz9WVdEIvamMCcXmuqUYjTknH/sqsWvhQ3vgwKFRR1HpjvNBKQ37nbJgYzGqGcg==}
     engines: {node: '>=6'}
@@ -3583,6 +3591,8 @@ snapshots:
 
   mime@1.6.0: {}
 
+  mime@4.0.4: {}
+
   mimic-fn@2.1.0: {}
 
   min-indent@1.0.1: {}