Fix weird file extension

Normalize file extension when getting download.

src/common.ts

@@ -4,11 +4,16 @@ type ProcessEventCallback = (event: ProcessEvent) => void;
 
 type ErrorEventCallback = (event: Error) => void;
 
+type SuccessEvent = { type: string, output: Buffer };
+
+type SuccessEventCallback = (event: SuccessEvent) => void;
+
 export interface VideoClipEventEmitter extends NodeJS.EventEmitter {
   process(): void;
   on(eventType: 'process', callback: ProcessEventCallback): this;
   on(eventType: 'error', callback: ErrorEventCallback): this;
   on(eventType: 'end', callback: ErrorEventCallback): this;
+  on(eventType: 'success', callback: SuccessEventCallback): this;
 }
 
 export const FILE_TYPES: Record<string, string> = {

src/video-types/youtube.ts

@@ -35,7 +35,7 @@ const getFileExtension = (downloaderExecutablePath: string, url: string) => {
     throw result.error;
   }
 
-  return result.stdout.toString('utf-8');
+  return result.stdout.toString('utf-8').trim();
 };
 
 const constructDownloadSectionsRegex = (start?: number | string, end?: number | string) => {