obs-ffmpeg: Fix ffmpeg-mux unicode file saving (win32)

On windows, if you were saving a file name or directory with characters
that are not of the current windows character set, it could cause the
file saving process to fail.  This fixes it so that on windows it uses
wmain and converts the unicode command line to a UTF-8 command line,
which works with FFmpeg.

plugins/obs-ffmpeg/ffmpeg-mux/ffmpeg-mux.c

@@ -17,6 +17,7 @@
 #ifdef _WIN32
 #include <io.h>
 #include <fcntl.h>
+#include <windows.h>
 #define inline __inline
 
 #endif
@@ -629,7 +630,11 @@ static inline bool ffmpeg_mux_packet(struct ffmpeg_mux *ffm, uint8_t *buf,
 
 /* ------------------------------------------------------------------------- */
 
+#ifdef _WIN32
+int wmain(int argc, wchar_t *argv_w[])
+#else
 int main(int argc, char *argv[])
+#endif
 {
 	struct ffm_packet_info info = {0};
 	struct ffmpeg_mux ffm = {0};
@@ -638,6 +643,21 @@ int main(int argc, char *argv[])
 	int ret;
 
 #ifdef _WIN32
+	char **argv;
+
+	argv = malloc(argc * sizeof(char*));
+	for (int i = 0; i < argc; i++) {
+		size_t len = wcslen(argv_w[i]);
+		int size;
+
+		size = WideCharToMultiByte(CP_UTF8, 0, argv_w[i], len, NULL, 0,
+				NULL, NULL);
+		argv[i] = malloc(size + 1);
+		WideCharToMultiByte(CP_UTF8, 0, argv_w[i], len, argv[i],
+				size + 1, NULL, NULL);
+		argv[i][size] = 0;
+	}
+
 	_setmode(_fileno(stdin), O_BINARY);
 #endif
 	setvbuf(stderr, NULL, _IONBF, 0);
@@ -660,5 +680,11 @@ int main(int argc, char *argv[])
 
 	ffmpeg_mux_free(&ffm);
 	resize_buf_free(&rb);
+
+#ifdef _WIN32
+	for (int i = 0; i < argc; i++)
+		free(argv[i]);
+	free(argv);
+#endif
 	return 0;
 }