Add VideoFrame Metadata Registry to the Readme

Author: chrisn

README.md

@@ -9,12 +9,12 @@ Many Web APIs use media codecs internally to support APIs for particular uses:
 - MediaRecorder
 - WebRTC
 
-But there’s no general way to flexibly configure and use these media codecs. 
-Because of this, many web applications have resorted to implementing 
+But there’s no general way to flexibly configure and use these media codecs.
+Because of this, many web applications have resorted to implementing
 media codecs in JavaScript or WebAssembly, despite the disadvantages:
 - Increased bandwidth to download codecs already in the browser.
 - Reduced performance
-- Reduced power efficiency 
+- Reduced power efficiency
 
 It's great for:
 - Live streaming
@@ -27,12 +27,20 @@ See the [explainer](https://github.com/w3c/webcodecs/blob/main/explainer.md) for
 
 Please see https://w3c.github.io/webcodecs/samples/
 
-## WebCodecs Codec Registry
+## WebCodecs registries
 
-This repository also contains the
-[WebCodecs Codec Registry](https://w3c.github.io/webcodecs/codec_registry.html),
-which provides the means to identify and avoid collisions among codec strings
+This repository also contains two registries:
+
+* The [WebCodecs Codec Registry](https://w3c.github.io/webcodecs/codec_registry.html)
+provides the means to identify and avoid collisions among codec strings
 used in WebCodecs and provides a mechanism to define codec-specific members of
 WebCodecs codec configuration dictionaries. Codec-specific registrations entered
 in the registry are also maintained in the repository, please refer to the
 registry for a comprehensive list.
+
+* The [WebCodecs VideoFrame Metadata Registry](https://w3c.github.io/webcodecs/video_frame_metadata_registry.html)
+enumerates the metadata fields that can be attached to
+[VideoFrame](https://w3c.github.io/webcodecs/#videoframe-interface) objects via the
+[VideoFrameMetadata](https://w3c.github.io/webcodecs/#dictdef-videoframemetadata) dictionary.
+Metadata registrations entered in the registry may be maintained in this repository
+or elsewhere. Please refer to the registry for a comprehensive list.