lavf/segment: simplify segment_count update

Now segment_count mark the segment_count of the current segment.

libavformat/segment.c

@@ -187,7 +187,6 @@ static int segment_start(AVFormatContext *s, int write_header)
     seg->segment_idx++;
     if ((err = set_segment_filename(s)) < 0)
         return err;
-    seg->segment_count++;
 
     if ((err = avio_open2(&oc->pb, oc->filename, AVIO_FLAG_WRITE,
                           &s->interrupt_callback, NULL)) < 0)
@@ -594,7 +593,6 @@ static int seg_write_header(AVFormatContext *s)
 
     if ((ret = set_segment_filename(s)) < 0)
         goto fail;
-    seg->segment_count++;
 
     if (seg->write_header_trailer) {
         if ((ret = avio_open2(&oc->pb, oc->filename, AVIO_FLAG_WRITE,
@@ -641,13 +639,13 @@ static int seg_write_packet(AVFormatContext *s, AVPacket *pkt)
     int ret;
 
     if (seg->times) {
-        end_pts = seg->segment_count <= seg->nb_times ?
-            seg->times[seg->segment_count-1] : INT64_MAX;
+        end_pts = seg->segment_count < seg->nb_times ?
+            seg->times[seg->segment_count] : INT64_MAX;
     } else if (seg->frames) {
         start_frame = seg->segment_count <= seg->nb_frames ?
-            seg->frames[seg->segment_count-1] : INT_MAX;
+            seg->frames[seg->segment_count] : INT_MAX;
     } else {
-        end_pts = seg->time * seg->segment_count;
+        end_pts = seg->time * (seg->segment_count+1);
     }
 
     av_dlog(s, "packet stream:%d pts:%s pts_time:%s is_key:%d frame:%d\n",