avformat/segment: export inner muxer timebase

Fixes "Non-monotonous DTS in output stream 0:0"
Fixes Ticket4020

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/segment.c

@@ -570,6 +570,7 @@ static int seg_write_header(AVFormatContext *s)
     AVFormatContext *oc = NULL;
     AVDictionary *options = NULL;
     int ret;
+    int i;
 
     seg->segment_count = 0;
     if (!seg->write_header_trailer)
@@ -675,6 +676,13 @@ static int seg_write_header(AVFormatContext *s)
     }
     seg->segment_frame_count = 0;
 
+    av_assert0(s->nb_streams == oc->nb_streams);
+    for (i = 0; i < s->nb_streams; i++) {
+        AVStream *inner_st  = oc->streams[i];
+        AVStream *outer_st = s->streams[i];
+        avpriv_set_pts_info(outer_st, inner_st->pts_wrap_bits, inner_st->time_base.num, inner_st->time_base.den);
+    }
+
     if (oc->avoid_negative_ts > 0 && s->avoid_negative_ts < 0)
         s->avoid_negative_ts = 1;