make릭ع a few f梦nctions have return types + etc

src/constants/keyFormats.ts

@@ -0,0 +1,4 @@
+// https://developer.apple.com/documentation/http-live-streaming/using-content-protection-systems-with-hls#Choose-a-key-format
+export const widevine = "urn:uuid:edef8ba9-79d6-4ace-a3c8-27dcd51d21ed";
+export const playready = "com.microsoft.playready";
+export const fairplay = "com.apple.streamingkeydelivery";