Use STV-AV1 encoder for AV1.

STV-AV1 is much, much faster than the reference libaom encoder. In most real-world cases libaom is too slow to be practical, often struggling to achieve 0.1fps for 1080p content.

I suspect this is what was intended in f1ca179 when AV1 support was originally added as it sets the `-svtav1-params` flag which is ignored unless using the STV-AV1 encoder. Furthermore there is lots of discussion about STV-AV1 in the PR thread.

server/src/services/media.service.spec.ts

@@ -1322,7 +1322,7 @@ describe(MediaService.name, () => {
         expect.objectContaining({
           inputOptions: expect.any(Array),
           outputOptions: expect.arrayContaining([
-            '-c:v av1',
+            '-c:v libsvtav1',
             '-movflags faststart',
             '-fps_mode passthrough',
             '-map 0:0',

server/src/utils/media.ts

@@ -492,6 +492,10 @@ export class VP9Config extends BaseConfig {
 }
 
 export class AV1Config extends BaseConfig {
+  getVideoCodec(): string {
+    return 'libsvtav1';
+  }
+
   getPresetOptions() {
     const speed = this.getPresetIndex() + 4; // Use 4 as slowest, giving us an effective range of 4-12 which is far more useful than 0-8
     if (speed >= 0) {