feat(drm): ✨ Add support for mp4decrypt as a decryption method

* Introduced a new configuration option for DRM decryption in `unshackle.yaml`.
* Updated the `decrypt` methods in `PlayReady` and `Widevine` classes to allow using `mp4decrypt`.
* Enhanced the `Config` class to manage decryption methods per service.
* Added `mp4decrypt` binary detection in the binaries module.

unshackle/core/drm/playready.py

@@ -187,14 +187,69 @@ class PlayReady:
         if not self.content_keys:
             raise PlayReady.Exceptions.EmptyLicense("No Content Keys were within the License")
 
-    def decrypt(self, path: Path) -> None:
+    def decrypt(self, path: Path, use_mp4decrypt: bool = False) -> None:
+        """
+        Decrypt a Track with PlayReady DRM.
+        Args:
+            path: Path to the encrypted file to decrypt
+            use_mp4decrypt: If True, use mp4decrypt instead of Shaka Packager
+        Raises:
+            EnvironmentError if the required decryption executable could not be found.
+            ValueError if the track has not yet been downloaded.
+            SubprocessError if the decryption process returned a non-zero exit code.
+        """
         if not self.content_keys:
             raise ValueError("Cannot decrypt a Track without any Content Keys...")
-        if not binaries.ShakaPackager:
-            raise EnvironmentError("Shaka Packager executable not found but is required.")
+
         if not path or not path.exists():
             raise ValueError("Tried to decrypt a file that does not exist.")
 
+        if use_mp4decrypt:
+            return self._decrypt_with_mp4decrypt(path)
+        else:
+            return self._decrypt_with_shaka_packager(path)
+
+    def _decrypt_with_mp4decrypt(self, path: Path) -> None:
+        """Decrypt using mp4decrypt"""
+        if not binaries.Mp4decrypt:
+            raise EnvironmentError("mp4decrypt executable not found but is required.")
+
+        output_path = path.with_stem(f"{path.stem}_decrypted")
+
+        # Build key arguments
+        key_args = []
+        for kid, key in self.content_keys.items():
+            kid_hex = kid.hex if hasattr(kid, "hex") else str(kid).replace("-", "")
+            key_hex = key if isinstance(key, str) else key.hex()
+            key_args.extend(["--key", f"{kid_hex}:{key_hex}"])
+
+        cmd = [
+            str(binaries.Mp4decrypt),
+            "--show-progress",
+            *key_args,
+            str(path),
+            str(output_path),
+        ]
+
+        try:
+            subprocess.run(cmd, check=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True)
+        except subprocess.CalledProcessError as e:
+            error_msg = e.stderr if e.stderr else f"mp4decrypt failed with exit code {e.returncode}"
+            raise subprocess.CalledProcessError(e.returncode, cmd, output=e.stdout, stderr=error_msg)
+
+        if not output_path.exists():
+            raise RuntimeError(f"mp4decrypt failed: output file {output_path} was not created")
+        if output_path.stat().st_size == 0:
+            raise RuntimeError(f"mp4decrypt failed: output file {output_path} is empty")
+
+        path.unlink()
+        shutil.move(output_path, path)
+
+    def _decrypt_with_shaka_packager(self, path: Path) -> None:
+        """Decrypt using Shaka Packager (original method)"""
+        if not binaries.ShakaPackager:
+            raise EnvironmentError("Shaka Packager executable not found but is required.")
+
         output_path = path.with_stem(f"{path.stem}_decrypted")
         config.directories.temp.mkdir(parents=True, exist_ok=True)