Make OutputContainer.metadata lazy

Author: WyattBlue

av/container/core.pxd

@@ -34,7 +34,7 @@ cdef class Container:
     cdef HWAccel hwaccel
 
     cdef readonly StreamContainer streams
-    cdef readonly dict metadata
+    cdef dict _metadata
 
     # Private API.
     cdef uint8_t _myflag  # enum: writeable, input_was_opened, started, done, extradata_planned

av/container/core.py

@@ -414,6 +414,14 @@ def flags(self, value: cython.int):
     def input_was_opened(self):
         return self._myflag & 2
 
+    @property
+    def metadata(self) -> dict:
+        # Lazily created so output containers that never touch metadata don't
+        # allocate a dict. Input containers populate ``_metadata`` eagerly.
+        if self._metadata is None:
+            self._metadata = {}
+        return self._metadata
+
     def chapters(self):
         self._assert_open()
         result: list = []

av/container/input.py

@@ -101,7 +101,7 @@ def __cinit__(self, *args, **kwargs):
                 "Hardware accelerated decode requested but no stream is compatible"
             )
 
-        self.metadata = avdict_to_dict(
+        self._metadata = avdict_to_dict(
             self.ptr.metadata, self.metadata_encoding, self.metadata_errors
         )
 

av/container/output.py

@@ -67,7 +67,6 @@ def close_output(self: OutputContainer):
 class OutputContainer(Container):
     def __cinit__(self, *args, **kwargs):
         self.streams = StreamContainer()
-        self.metadata = {}
         self._extradata_bsfs = {}
         self._buffered_packets = []
         with cython.nogil: