avformat/utils: add a function to standardize creation time

This can be used for formats which write all format metadata as string to
files, therefore non-standard creation times such as 'now' will be parsed.

The standardized creation time is UTC ISO 8601 with microsecond precision.
Reviewed-by: wm4 <nfxjfg@googlemail.com>
Signed-off-by: Marton Balint <cus@passwd.hu>

libavformat/internal.h

@@ -560,6 +560,14 @@ void ff_format_io_close(AVFormatContext *s, AVIOContext **pb);
  */
 int ff_parse_creation_time_metadata(AVFormatContext *s, int64_t *timestamp, int return_seconds);
 
+/**
+ * Standardize creation_time metadata in AVFormatContext to an ISO-8601
+ * timestamp string.
+ *
+ * @param s AVFormatContext
+ * @return <0 on error
+ */
+int ff_standardize_creation_time(AVFormatContext *s);
 
 #define CONTAINS_PAL 2
 /**

libavformat/utils.c

@@ -33,6 +33,7 @@
 #include "libavutil/parseutils.h"
 #include "libavutil/pixdesc.h"
 #include "libavutil/time.h"
+#include "libavutil/time_internal.h"
 #include "libavutil/timestamp.h"
 
 #include "libavcodec/bytestream.h"
@@ -4760,6 +4761,27 @@ int ff_parse_creation_time_metadata(AVFormatContext *s, int64_t *timestamp, int
     return 0;
 }
 
+int ff_standardize_creation_time(AVFormatContext *s)
+{
+    int64_t timestamp;
+    int ret = ff_parse_creation_time_metadata(s, &timestamp, 0);
+    if (ret == 1) {
+        time_t seconds = timestamp / 1000000;
+        struct tm *ptm, tmbuf;
+        ptm = gmtime_r(&seconds, &tmbuf);
+        if (ptm) {
+            char buf[32];
+            if (!strftime(buf, sizeof(buf), "%Y-%m-%dT%H:%M:%S", ptm))
+                return AVERROR_EXTERNAL;
+            av_strlcatf(buf, sizeof(buf), ".%06dZ", (int)(timestamp % 1000000));
+            av_dict_set(&s->metadata, "creation_time", buf, 0);
+        } else {
+            return AVERROR_EXTERNAL;
+        }
+    }
+    return ret;
+}
+
 int ff_get_packet_palette(AVFormatContext *s, AVPacket *pkt, int ret, const uint8_t **palette)
 {
     int size;

libavformat/version.h

@@ -31,7 +31,7 @@
 
 #define LIBAVFORMAT_VERSION_MAJOR  57
 #define LIBAVFORMAT_VERSION_MINOR  27
-#define LIBAVFORMAT_VERSION_MICRO 101
+#define LIBAVFORMAT_VERSION_MICRO 102
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
                                                LIBAVFORMAT_VERSION_MINOR, \