ffmpeg_opt: Fix starttime with ffm in bitexact mode

This fixes some differences between runs of the ffserver tests
(in my local tree 2 runs gave the same result with this but i had other
 changes too)

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

ffmpeg_opt.c

@@ -2046,7 +2046,7 @@ static int open_output_file(OptionsContext *o, const char *filename)
     InputStream  *ist;
     AVDictionary *unused_opts = NULL;
     AVDictionaryEntry *e = NULL;
-
+    int format_flags = 0;
 
     if (o->stop_time != INT64_MAX && o->recording_time != INT64_MAX) {
         o->stop_time = INT64_MAX;
@@ -2092,6 +2092,12 @@ static int open_output_file(OptionsContext *o, const char *filename)
     file_oformat= oc->oformat;
     oc->interrupt_callback = int_cb;
 
+    e = av_dict_get(o->g->format_opts, "fflags", NULL, 0);
+    if (e) {
+        const AVOption *o = av_opt_find(oc, "fflags", NULL, 0, 0);
+        av_opt_eval_flags(oc, o, e->value, &format_flags);
+    }
+
     /* create streams for all unlabeled output pads */
     for (i = 0; i < nb_filtergraphs; i++) {
         FilterGraph *fg = filtergraphs[i];
@@ -2112,6 +2118,7 @@ static int open_output_file(OptionsContext *o, const char *filename)
 
     /* ffserver seeking with date=... needs a date reference */
     if (!strcmp(file_oformat->name, "ffm") &&
+        !(format_flags & AVFMT_FLAG_BITEXACT) &&
         av_strstart(filename, "http:", NULL)) {
         int err = parse_option(o, "metadata", "creation_time=now", options);
         if (err < 0) {