driver/httpvideodriver: implement screenshot

Implement screenshots for HTTP video cameras. For this we factor out the
default_port function out of stream() and reuse it for screenshot().

The screenshot function takes the stream, waits for 75 buffers to ensure
we have hit an i-frame in the pipeline so we can encode a complete
picture and than encodes the picture into a jpeg file.

Signed-off-by: Rouven Czerwinski <[email protected]>

labgrid/driver/httpvideodriver.py

@@ -20,16 +20,20 @@ class HTTPVideoDriver(Driver, VideoProtocol):
     def get_qualities(self):
         return ("high", [("high", None)])
 
-    @Driver.check_active
-    def stream(self, quality_hint=None):
+    def _get_default_port(self):
         s = urlsplit(self.video.url)
         if s.scheme == "http":
             default_port = 80
         elif s.scheme == "https":
             default_port = 443
         else:
             print(f"Unknown scheme: {s.scheme}", file=sys.stderr)
-            return
+            return None
+
+
+    @Driver.check_active
+    def stream(self, quality_hint=None):
+        default_port = self._get_default_port()
 
         url = proxymanager.get_url(self.video.url, default_port=default_port)
         pipeline = [
@@ -47,3 +51,25 @@ def stream(self, quality_hint=None):
 
         sub = subprocess.run(pipeline)
         return sub.returncode
+
+    @Driver.check_active
+    def screenshot(self, filename):
+        default_port = self._get_default_port()
+
+        url = proxymanager.get_url(self.video.url, default_port=default_port)
+        pipeline = [
+            "gst-launch-1.0",
+            "souphttpsrc",
+            "num-buffers=75",
+            f"location={url}",
+            "!",
+            "decodebin",
+            "!",
+            "jpegenc",
+            "!",
+            "filesink",
+            f"location={filepath.absolute()}"
+        ]
+
+        sub = subprocess.run(pipeline)
+        return sub.returncode