flvmux: Set PTS based on running time

https://bugzilla.gnome.org/show_bug.cgi?id=793457
diff --git a/gst/flv/gstflvmux.c b/gst/flv/gstflvmux.c
index 7e3aab4..c3ec66c 100644
--- a/gst/flv/gstflvmux.c
+++ b/gst/flv/gstflvmux.c
@@ -1171,7 +1171,12 @@
     /* if we are streamable we copy over timestamps and offsets,
        if not just copy the offsets */
     if (mux->streamable) {
-      gst_buffer_copy_into (tag, buffer, GST_BUFFER_COPY_TIMESTAMPS, 0, -1);
+      GstClockTime timestamp = GST_CLOCK_TIME_NONE;
+
+      if (gst_segment_to_running_time_full (&GST_AGGREGATOR_PAD (pad)->segment,
+              GST_FORMAT_TIME, GST_BUFFER_DTS_OR_PTS (buffer), &timestamp) == 1)
+        GST_BUFFER_PTS (tag) = timestamp;
+
       GST_BUFFER_OFFSET (tag) = GST_BUFFER_OFFSET_NONE;
       GST_BUFFER_OFFSET_END (tag) = GST_BUFFER_OFFSET_NONE;
     } else {