lavc: Document AV_PKT_DATA_NEW_EXTRADATA

libavcodec/avcodec.h

@@ -1187,6 +1187,14 @@ typedef struct AVCPBProperties {
  */
 enum AVPacketSideDataType {
     AV_PKT_DATA_PALETTE,
+
+    /**
+     * The AV_PKT_DATA_NEW_EXTRADATA is used to notify the codec or the format
+     * that the extradata buffer was changed and the receiving side should
+     * act upon it appropriately. The new extradata is embedded in the side
+     * data buffer and should be immediately used for processing the current
+     * frame or packet.
+     */
     AV_PKT_DATA_NEW_EXTRADATA,
 
     /**