libobs/util: Add %s string replacement for unix time

Adds %s which replaces the keyword with the current unix epoch time.

The %s keyword is common in languages like PHP and Python, and even
some C implementations, but it is not standard so this is a fallback.

UI/data/locale/en-US.ini

@@ -975,7 +975,7 @@ Screenshot.Source="Screenshot (Source)"
 FilenameFormatting.completer="%CCYY-%MM-%DD %hh-%mm-%ss\n%YY-%MM-%DD %hh-%mm-%ss\n%Y-%m-%d %H-%M-%S\n%y-%m-%d %H-%M-%S\n%a %Y-%m-%d %H-%M-%S\n%A %Y-%m-%d %H-%M-%S\n%Y-%b-%d %H-%M-%S\n%Y-%B-%d %H-%M-%S\n%Y-%m-%d %I-%M-%S-%p\n%Y-%m-%d %H-%M-%S-%z\n%Y-%m-%d %H-%M-%S-%Z\n%FPS\n%CRES\n%ORES\n%VF"
 
 # basic mode 'output' settings - advanced section - recording subsection - TT
-FilenameFormatting.TT="%CCYY	Year, four digits\n%YY		Year, last two digits (00-99)\n%MM		Month as a decimal number (01-12)\n%DD		Day of the month, zero-padded (01-31)\n%hh		Hour in 24h format (00-23)\n%mm		Minute (00-59)\n%ss		Second (00-61)\n%%		A % sign\n%a		Abbreviated weekday name\n%A		Full weekday name\n%b		Abbreviated month name\n%B		Full month name\n%d		Day of the month, zero-padded (01-31)\n%H		Hour in 24h format (00-23)\n%I		Hour in 12h format (01-12)\n%m		Month as a decimal number (01-12)\n%M		Minute (00-59)\n%p		AM or PM designation\n%S		Second (00-61)\n%y		Year, last two digits (00-99)\n%Y		Year\n%z		ISO 8601 offset from UTC in timezone\n%Z		Timezone name or abbreviation\n%FPS		Frames per second\n%CRES		Base (canvas) resolution\n%ORES		Output (scaled) resolution\n%VF		Video format"
+FilenameFormatting.TT="%CCYY	Year, four digits\n%YY		Year, last two digits (00-99)\n%MM		Month as a decimal number (01-12)\n%DD		Day of the month, zero-padded (01-31)\n%hh		Hour in 24h format (00-23)\n%mm		Minute (00-59)\n%ss		Second (00-61)\n%%		A % sign\n%a		Abbreviated weekday name\n%A		Full weekday name\n%b		Abbreviated month name\n%B		Full month name\n%d		Day of the month, zero-padded (01-31)\n%H		Hour in 24h format (00-23)\n%I		Hour in 12h format (01-12)\n%m		Month as a decimal number (01-12)\n%M		Minute (00-59)\n%p		AM or PM designation\n%s		Time in seconds since UNIX epoch\n%S		Second (00-61)\n%y		Year, last two digits (00-99)\n%Y		Year\n%z		ISO 8601 offset from UTC in timezone\n%Z		Timezone name or abbreviation\n%FPS		Frames per second\n%CRES		Base (canvas) resolution\n%ORES		Output (scaled) resolution\n%VF		Video format"
 
 # basic mode 'video' settings
 Basic.Settings.Video="Video"

libobs/util/platform.c

@@ -19,6 +19,7 @@
 #include <time.h>
 #include <errno.h>
 #include <stdlib.h>
+#include <inttypes.h>
 #include <locale.h>
 #include "c99defs.h"
 #include "platform.h"
@@ -782,6 +783,10 @@ char *os_generate_formatted_filename(const char *extension, bool space,
 				strcpy(convert, get_video_format_name(
 							ovi.output_format));
 				replace_text(&sf, pos, 3, convert);
+
+			} else if (astrcmp_n(cmp, "%s", 2) == 0) {
+				sprintf(convert, "%" PRId64, (int64_t)now);
+				replace_text(&sf, pos, 2, convert);
 			}
 		}