🔧(frontend) default to vp9 for video codec

As a mandatory codec in WebRTC specifications, VP8 serves as
the baseline for compatibility, making it the default choice
in LiveKit client configuration.

There is room for optimization.

Newer codecs like VP9 offer significant efficiency gains
compared to VP8, with a 23-33% improvement in compression
efficiency. This translates to better video quality at
the same bitrate or reduced bandwidth usage for the same quality.

VP9 is supported in Safari starting from version 15.0+,
and Firefox offers partial support. However, Firefox lacks
support for VP9's Scalable Video Coding (SVC).

With SVC, participants can send a single VP9 stream
with multiple spatial or temporal layers. This allows receivers
to dynamically adjust video quality by using lower layers when
resolution or bandwidth needs to be reduced, improving
adaptability in heterogeneous network conditions.

Simulcast, by contrast, sends multiple separate streams
at different resolutions. While widely supported in VP8 and VP9,
it consumes more bandwidth compared to SVC.

The configuration added here is based on the LiveKit demo app,
which defaults to VP9 when supported. OpenTalk’s configuration
also recommends VP9.

If a browser does not support VP9, LiveKit falls back to VP8 or
other codecs as needed. Notably, LiveKit disables VP9 encoding for
Firefox due to longstanding issues, but it can still decode VP9
streams and encode VP8 for outgoing streams. This ensures
compatibility with other participants, even in mixed environments
where some browsers use VP9 and others fallback to VP8.

In theory, participants do not all need to switch to a single codec,
as both LiveKit and browsers intelligently handle codec negotiation
on a per-participant basis. This dynamic adaptation ensures seamless
communication without manual intervention.

A similar challenge with codec compatibility was raised
in Jitsi two years ago, check issue #10657.

Before any release, this needs to be battle tested
with Firefox 115 browsers.

src/frontend/src/features/rooms/components/Conference.tsx

@@ -65,6 +65,9 @@ export const Conference = ({
 
   const roomOptions = useMemo((): RoomOptions => {
     return {
+      publishDefaults: {
+        videoCodec: 'vp9',
+      },
       videoCaptureDefaults: {
         deviceId: userConfig.videoDeviceId ?? undefined,
       },