This means you clicked "Start" without selecting any video/audio file first.
Click the "Select audio or video" button at the top-left of the main window and choose your file (mp4/mkv/avi/mov/wav/mp3).
If you want to batch process a whole directory, tick the "Folder" option, then select the folder.
After the file path appears in the input box, click "Start Execution".
Additional note for your setup: your software is at root_dir:C:/Users/Asus/Downloads/Compressed/New folder (5). This path contains spaces and parentheses, which frequently causes FFmpeg/path failures later. Strongly recommended: move the software to a simple English path such as D:\pyVideoTrans before processing.
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