Advanced decryption requires a valid CDM (like a Widevine L3 device certificate) to simulate a legitimate player and request keys from the server. Tools for Handling MPD Files
Unless the video uses "Clear Key" (where the key is publicly visible), you will need a to extract the keys from the license server.
allow users to input an MPD URI and a known key pair to automate the process of downloading segments, merging them, and outputting a decrypted MP4. Key Extraction