avfilter/drawtext: present 'hms' formatted 'pts' in 24h format

HMS is formatted as HH:MM:SS.mmm, but, HH part is not limited to
24 hours. For example, the the drawn text may look like this:
243029:20:30.342. To present the timestamp in more readable and
user friendly format, this patch provides an additional option
to limit the hour part in the range 0-23.

Note: Actually the above required format can be obtained with
format options 'localtime' and 'gmtime', but,  milliseconds part
is not supported in those formats.

doc/filters.texi

@@ -8257,6 +8257,10 @@ local time zone time.
 
 The second argument is an offset added to the timestamp.
 
+If the format is set to @code{hms}, a third argument @code{24HH} may be
+supplied to present the hour part of the formatted timestamp in 24h format
+(00-23).
+
 If the format is set to @code{localtime} or @code{gmtime},
 a third argument may be supplied: a strftime() format string.
 By default, @var{YYYY-MM-DD HH:MM:SS} format will be used.

libavfilter/vf_drawtext.c

@@ -916,6 +916,14 @@ static int func_pts(AVFilterContext *ctx, AVBPrint *bp,
                 sign = '-';
                 ms = -ms;
             }
+            if (argc >= 3) {
+                if (!strcmp(argv[2], "24HH")) {
+                    ms %= 24 * 60 * 60 * 1000;
+                } else {
+                    av_log(ctx, AV_LOG_ERROR, "Invalid argument '%s'\n", argv[2]);
+                    return AVERROR(EINVAL);
+                }
+            }
             av_bprintf(bp, "%c%02d:%02d:%02d.%03d", sign,
                        (int)(ms / (60 * 60 * 1000)),
                        (int)(ms / (60 * 1000)) % 60,