Update ffmpeg.py

Problem:
I created a yt-dlp GUI and I use ffmpeg to convert to audio often, recently I used pyinstaller to make a .exe for this GUI because I want to send it to friends who don't have python in their computers, also I don't like the console that appears with python so I just put the configuration to remove the console on pyinstaller, the program works fine, until it has to convert anything with ffmpeg, then because ffmpeg requires a console to open it the program crashes.

Solution:
Added 'creationflags=subprocess.CREATE_NO_WINDOW' so it doesn't try to create a terminal window, this fixes the crashing.

Extra info:
- All of this is on windows, I didn't test on linux or on mac
- This problem only happend to me when I compiled the program to .exe
- I tried this solution and it worked perfectly

yt_dlp/postprocessor/ffmpeg.py

@@ -251,7 +251,8 @@ class FFmpegPostProcessor(PostProcessor):
             cmd.append(encodeFilename(self._ffmpeg_filename_argument(path), True))
             self.write_debug(f'{self.basename} command line: {shell_quote(cmd)}')
             stdout, stderr, returncode = Popen.run(
-                cmd, text=True, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+                cmd, text=True, stdin=subprocess.PIPE, stdout=subprocess.PIPE,
+                stderr=subprocess.PIPE, creationflags=subprocess.CREATE_NO_WINDOW)
             if returncode != (0 if self.probe_available else 1):
                 return None
         except OSError:
@@ -292,7 +293,8 @@ class FFmpegPostProcessor(PostProcessor):
         cmd += opts
         cmd.append(self._ffmpeg_filename_argument(path))
         self.write_debug(f'ffprobe command line: {shell_quote(cmd)}')
-        stdout, _, _ = Popen.run(cmd, text=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE)
+        stdout, _, _ = Popen.run(cmd, text=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
+                                 stdin=subprocess.PIPE, creationflags=subprocess.CREATE_NO_WINDOW)
         return json.loads(stdout)
 
     def get_stream_number(self, path, keys, value):
@@ -361,7 +363,8 @@ class FFmpegPostProcessor(PostProcessor):
 
         self.write_debug('ffmpeg command line: %s' % shell_quote(cmd))
         _, stderr, returncode = Popen.run(
-            cmd, text=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE)
+            cmd, text=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
+            stdin=subprocess.PIPE, creationflags=subprocess.CREATE_NO_WINDOW)
         if returncode not in variadic(expected_retcodes):
             self.write_debug(stderr)
             raise FFmpegPostProcessorError(stderr.strip().splitlines()[-1])