🐛 StreamGear: Refactor stream copy handling (Fixes #396)

💬 When the output codec is set to "copy" (stream copy mode), certain video
processing parameters like "-vf" (video filters) and "-aspect" (aspect ratio)
are not supported and can lead to errors and invalid output files.

♻️ This commit refactors the internal `PreProcess` method in StreamGear API to handle
the stream copy mode correctly:

- 🥅 Moved the existing code for setting "-vf" and "-aspect" inside conditional block that checks if
  the output stream codec is not "copy".
- 🔊 Added an else block to log warnings and discard "-vf" and "-aspect" in stream copy mode.

vidgear/gears/streamgear.py

@@ -425,11 +425,21 @@ def __PreProcess(self, channels=0, rgb=False):
         default_codec = "libx264rgb" if rgb else "libx264"
         output_parameters["-vcodec"] = self.__params.pop("-vcodec", default_codec)
         # enable optimizations and enforce compatibility
-        output_parameters["-vf"] = self.__params.pop("-vf", "format=yuv420p")
-        aspect_ratio = Fraction(
-            self.__inputwidth / self.__inputheight
-        ).limit_denominator(10)
-        output_parameters["-aspect"] = ":".join(str(aspect_ratio).split("/"))
+        if output_parameters["-vcodec"] != "copy":
+            # NOTE: these parameters only supported when stream copy not defined
+            output_parameters["-vf"] = self.__params.pop("-vf", "format=yuv420p")
+            aspect_ratio = Fraction(
+                self.__inputwidth / self.__inputheight
+            ).limit_denominator(10)
+            output_parameters["-aspect"] = ":".join(str(aspect_ratio).split("/"))
+        else:
+            # log warnings for these parameters
+            self.__params.pop("-vf", False) and logger.warning(
+                "Filtering and stream copy cannot be used together. Discarding `-vf` parameter!"
+            )
+            self.__params.pop("-aspect", False) and logger.warning(
+                "Overriding aspect ratio with stream copy may produce invalid files. Discarding `-aspect` parameter!"
+            )
         # w.r.t selected codec
         if output_parameters["-vcodec"] in [
             "libx264",