PSSH: Allow crafting v0 boxes with just Key IDs

This is actually possible and in some cases necessary. While v0 boxes do not use key_IDs field of the PSSH Box, we can store the provided key_ids in the init data. E.g., Apple Music.

pywidevine/pssh.py

@@ -126,11 +126,9 @@ class PSSH:
         if flags < 0:
             raise ValueError(f"Invalid flags, cannot be less than 0.")
 
-        if version == 0:
-            if key_ids is not None:
-                raise ValueError("Version 0 PSSH boxes must use init_data only, not key_ids.")
-            if init_data is None:
-                raise ValueError("Version 0 PSSH boxes must use init_data but it wasn't provided.")
+        if version == 0 and key_ids is not None and init_data is not None:
+            # v0 boxes use only init_data in the pssh field, but we can use the key_ids within the init_data
+            raise ValueError("Version 0 PSSH boxes must use only init_data, not init_data and key_ids.")
         elif version == 1:
             # TODO: I cannot tell if they need either init_data or key_ids exclusively, or both is fine
             #       So for now I will just make sure at least one is supplied
@@ -177,6 +175,9 @@ class PSSH:
             init_data=[init_data, b""][init_data is None]
         )))
 
+        if key_ids and version == 0:
+            PSSH.overwrite_key_ids(box, [UUID(bytes=x) for x in key_ids])
+
         return cls(box)
 
     @classmethod