avformat/segment: give a warning message for remove initial_offset option

ffmpeg have a generic solution working with all muxer named
output_ts_offset, output_ts_offset will instead of initial_offset
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/segment.c

@@ -651,6 +651,11 @@ static int seg_init(AVFormatContext *s)
         seg->individual_header_trailer = 0;
     }
 
+    if (seg->initial_offset > 0) {
+        av_log(s, AV_LOG_WARNING, "NOTE: the option initial_offset is deprecated,"
+               "you can use output_ts_offset instead of it\n");
+    }
+
     if (!!seg->time_str + !!seg->times_str + !!seg->frames_str > 1) {
         av_log(s, AV_LOG_ERROR,
                "segment_time, segment_times, and segment_frames options "