validate/baseclasses: Don't leak several hundred MB of XML

The xml-based MediaDescriptor were keeping open the XML file and the
associated ElementTree structures, resulting in memory usage of several
hundred megabytes.

Instead cache the information we need immediately and release the
XML structure

validate/launcher/baseclasses.py

@@ -2024,18 +2024,40 @@ class GstValidateMediaDescriptor(MediaDescriptor):
 
         self._xml_path = xml_path
         try:
-            self.media_xml = ET.parse(xml_path).getroot()
+            media_xml = ET.parse(xml_path).getroot()
         except xml.etree.ElementTree.ParseError:
             printc("Could not parse %s" % xml_path,
                    Colors.FAIL)
             raise
 
-        # Sanity checks
-        self.media_xml.attrib["duration"]
-        self.media_xml.attrib["seekable"]
+        self._extract_data (media_xml)
 
         self.set_protocol(urllib.parse.urlparse(urllib.parse.urlparse(self.get_uri()).scheme).scheme)
 
+    def _extract_data(self, media_xml):
+        # Extract the information we need from the xml
+        self._caps = media_xml.findall("streams")[0].attrib["caps"]
+        self._track_caps = []
+        try:
+            streams = media_xml.findall("streams")[0].findall("stream")
+        except IndexError:
+            pass
+        else:
+            for stream in streams:
+                self._track_caps.append((stream.attrib["type"], stream.attrib["caps"]))
+        self._uri = media_xml.attrib["uri"]
+        self._duration = int(media_xml.attrib["duration"])
+        self._protocol = media_xml.get("protocol", None)
+        self._is_seekable = media_xml.attrib["seekable"].lower() == "true"
+        self._is_live = media_xml.get("live", "false").lower() == "true"
+        self._is_image = False
+        for stream in media_xml.findall("streams")[0].findall("stream"):
+            if stream.attrib["type"] == "image":
+                self._is_image = True
+        self._track_types = []
+        for stream in media_xml.findall("streams")[0].findall("stream"):
+            self._track_types.append(stream.attrib["type"])
+
     @staticmethod
     def new_from_uri(uri, verbose=False, include_frames=False):
         """
@@ -2100,51 +2122,39 @@ class GstValidateMediaDescriptor(MediaDescriptor):
             return self._xml_path.replace("." + self.STREAM_INFO_EXT, "")
 
     def get_caps(self):
-        return self.media_xml.findall("streams")[0].attrib["caps"]
+        return self._caps
 
     def get_tracks_caps(self):
-        res = []
-        try:
-            streams = self.media_xml.findall("streams")[0].findall("stream")
-        except IndexError:
-            return res
-
-        for stream in streams:
-            res.append((stream.attrib["type"], stream.attrib["caps"]))
-
-        return res
+        return self._track_caps
 
     def get_uri(self):
-        return self.media_xml.attrib["uri"]
+        return self._uri
 
     def get_duration(self):
-        return int(self.media_xml.attrib["duration"])
+        return self._duration
 
     def set_protocol(self, protocol):
-        self.media_xml.attrib["protocol"] = protocol
+        self._protocol = protocol
 
     def get_protocol(self):
-        return self.media_xml.attrib["protocol"]
+        return self._protocol
 
     def is_seekable(self):
-        return self.media_xml.attrib["seekable"].lower() == "true"
+        return self._is_seekable
 
     def is_live(self):
-        return self.media_xml.get("live", "false").lower() == "true"
+        return self._is_live
 
     def can_play_reverse(self):
         return True
 
     def is_image(self):
-        for stream in self.media_xml.findall("streams")[0].findall("stream"):
-            if stream.attrib["type"] == "image":
-                return True
-        return False
+        return self._is_image
 
     def get_num_tracks(self, track_type):
         n = 0
-        for stream in self.media_xml.findall("streams")[0].findall("stream"):
-            if stream.attrib["type"] == track_type:
+        for t in self._track_types:
+            if t == track_type:
                 n += 1
 
         return n