add introduction

Author: palak8669

index.bs

@@ -448,7 +448,9 @@ interface RTCEncodedVideoFrame {
     </dt>
     <dd>
         <p>
-            Creates a new {{RTCEncodedVideoFrame}} from the given |originalFrame| and sets the internal metadata to |options|`[metadata]`.
+            Creates a new {{RTCEncodedVideoFrame}} from the given |originalFrame| and |options|`[metadata]`. The newly created frame is completely independent of the
+            |originalFrame| with its `[[data]]` being a deep copy of |originalFrame|.`[[data]]`. The new frame's `[[metadata]]` is a deep copy of |originalFrame|.`[[metadata]]`, with
+            any fields replaced with deep copies of the fields present in |options|`[metadata]`.
 
             When called, run the following steps:
 
@@ -674,8 +676,10 @@ interface RTCEncodedAudioFrame {
     </dt>
     <dd>
         <p>
-            Creates a new {{RTCEncodedAudioFrame}} from the given |originalFrame| and sets the internal metadata to |options|`[metadata]`.
-            
+            Creates a new {{RTCEncodedAudioFrame}} from the given |originalFrame| and |options|`[metadata]`. The newly created frame is completely independent of the
+            |originalFrame| with its `[[data]]` being a deep copy of |originalFrame|.`[[data]]`. The new frame's `[[metadata]]` is a deep copy of |originalFrame|.`[[metadata]]`, with
+            any fields replaced with deep copies of the fields present in |options|`[metadata]`.
+        
             When called, run the following steps:
 
             1. Let this.`[[data]]` be the result of [[CloneArrayBuffer]](|originalFrame|.`[[data]]`, 0, |originalFrame|.`[[data]]`.`[[ArrayBufferByteLength]]`).