libavformat/dashenc.c: Support mpd update period

According ISO 23009-1, in live cases, mpd refresh period should be configurable

Signed-off-by: Siyuan Huang <saber.huang@samsung.com>

doc/muxers.texi

@@ -366,6 +366,10 @@ adjusting playback latency and buffer occupancy during normal playback by client
 Set the maximum playback rate indicated as appropriate for the purposes of automatically
 adjusting playback latency and buffer occupancy during normal playback by clients.
 
+@item update_period @var{update_period}
+ Set the mpd update period ,for dynamic content.
+ The unit is second.
+
 @end table
 
 @anchor{framecrc}

libavformat/dashenc.c

@@ -198,6 +198,7 @@ typedef struct DASHContext {
     int target_latency_refid;
     AVRational min_playback_rate;
     AVRational max_playback_rate;
+    int64_t update_period;
 } DASHContext;
 
 static struct codec_string {
@@ -1184,6 +1185,8 @@ static int write_manifest(AVFormatContext *s, int final)
         char now_str[100];
         if (c->use_template && !c->use_timeline)
             update_period = 500;
+        if (c->update_period)
+            update_period = c->update_period;
         avio_printf(out, "\tminimumUpdatePeriod=\"PT%"PRId64"S\"\n", update_period);
         if (!c->ldash)
             avio_printf(out, "\tsuggestedPresentationDelay=\"PT%"PRId64"S\"\n", c->last_duration / AV_TIME_BASE);
@@ -2380,6 +2383,7 @@ static const AVOption options[] = {
     { "target_latency", "Set desired target latency for Low-latency dash", OFFSET(target_latency), AV_OPT_TYPE_DURATION, { .i64 = 0 }, 0, INT_MAX, E },
     { "min_playback_rate", "Set desired minimum playback rate", OFFSET(min_playback_rate), AV_OPT_TYPE_RATIONAL, { .dbl = 1.0 }, 0.5, 1.5, E },
     { "max_playback_rate", "Set desired maximum playback rate", OFFSET(max_playback_rate), AV_OPT_TYPE_RATIONAL, { .dbl = 1.0 }, 0.5, 1.5, E },
+    { "update_period", "Set the mpd update interval", OFFSET(update_period), AV_OPT_TYPE_INT64, {.i64 = 0}, 0, INT64_MAX, E},
     { NULL },
 };