String replace in .m3u8 file

Hello, how to replace some string from proxy_pass but from remote file ?!

proxy_pass http://domen.com/test/playlist.m3u8;
sub_filter 'EXTM3U' 'newstring';
sub_filter_once off;
subs_filter 'EXTM3U' 'newstring' i;

I can replace string if is not .m3u8 but if is on .m3u8 then I have a problem

Thanks