Revert "Change default video codec to VP9."

This reverts commit 69445d67.

README

@@ -173,13 +173,14 @@ nobody will be able to join the group.  The following fields are allowed:
  - `redirect`: if set, then attempts to join the group will be redirected
    to the given URL; most other fields are ignored in this case;
  - `codecs`: this is a list of codecs allowed in this group.  The default
-   is `["vp9", "opus"]`.
+   is `["vp8", "opus"]`.
    
 Supported video codecs include:
 
- - `"vp8"` (legacy, supported by all browsers);
- - `"vp9"` (compatible with all recent browsers);
- - `"av1"` (experimental, buggy in many browsers);
+ - `"vp8"` (compatible with all supported browsers);
+ - `"vp9"` (better video quality, but incompatible with Safari);
+ - `"av1"` (even better video quality, only supported by some browsers,
+   recording is not supported, SVC is not supported);
  - `"h264"` (incompatible with Debian and with some Android devices, SVC
    is not supported).
 

group/group.go

@@ -379,7 +379,7 @@ func APIFromCodecs(codecs []webrtc.RTPCodecParameters) (*webrtc.API, error) {
 
 func APIFromNames(names []string) (*webrtc.API, error) {
 	if len(names) == 0 {
-		names = []string{"vp9", "opus"}
+		names = []string{"vp8", "opus"}
 	}
 	var codecs []webrtc.RTPCodecParameters
 	for _, n := range names {