ffmpeg and subtitle .srt

Hello I'm a question!
Now I try to add subtitle .srt to mp4 by this suntax

Quote:

ffmpeg -i VideoSorgente.mp4 -i prova.srt -c:v copy -c:a copy -c:s mov_text -metadata:s:s:0 language=eng prova.mp4

than all work ok but on output I can read next lines

Quote:

[mp4 @ 0x1427940] Application provided duration: -1000 / timestamp: 160000 is out of range for mov/mp4 format [mp4 @ 0x1427940] pts has no value [mp4 @ 0x1427940] Application provided duration: -1 / timestamp: 168000 is out of range for mov/mp4 format [mp4 @ 0x1427940] pts has no value

If I understand it refers to some line on .srt file, but which? At the end if I open .mp4 file all subtitles are adde correctly.

PS:
I write .str file by Emacs and saved on UTF-8 format.
Thanks!