ffmpeg generate m3u8 from mp4 (Resume option) - multithreading

Question

I have a mp4 file or other file (non mp4 format) and i need generate ts files and m3u8 playlist.
I am using this command and works fine:
ffmpeg -i foo.mp4 -codec copy -vbsf h264_mp4toannexb -map 0 -f segment
-segment_list out.m3u8 -segment_time 10 out%03d.ts
Now I need to generate many ts simultaneous so i need a "resume option".
Please see the example below:
One thread (first 20 seconds (0-20))
ffmpeg -i foo.mp4 -codec copy -vbsf h264_mp4toannexb -map 0 -f segment
-segment_list out.m3u8 -segment_time 10 out%03d.ts
Seconds thread (20 seconds to 40 seconds)
ffmpeg -i foo.mp4 ......
Third thread (40 seconds to 60 seconds)
ffmpeg -i foo.mp4 ......
I have lots of core processor to do this jobs.
In resume i need generate .ts files and m3u8 fastest way possible
I need help or advises to resolve my problem.
Prove of concept i build a litle script that use -ss and -t option:
<?php
//generate all the commands using -ss and -t <seconds>
$startTime = new DateTime("00:00:00");
for ($i=1; $i < 20; $i++) {
$data = $startTime->format('H:i:s');
$exec = 'ffmpeg -i "<FILE>" -ss '.$data.' -t 10 -c:v copy -bsf h264_mp4toannexb -flags -global_header -map 0 -f segment -segment_time 10 -segment_start_number '.$i.' -segment_list '.sprintf("%04d", $i).'_test.m3u8 -segment_format mpegts '.$i.'stream%05d.ts';
shell_exec($exec);
$startTime->modify('+10 seconds');
echo "\n";
}
//cycle all m3u8 and creates a master hls playlist
$files = glob('*.{m3u8}', GLOB_BRACE);
sort($files);
$ret = "#EXTM3U
#EXT-X-VERSION:3
#EXT-X-MEDIA-SEQUENCE:0
#EXT-X-ALLOW-CACHE:YES
#EXT-X-TARGETDURATION:11
";
foreach($files as $file) {
$ret .= shell_exec('sed -n -e 6,7p '. $file);
}
$ret .= "#EXT-X-ENDLIST";
file_put_contents('final.m3u8', $ret);
?>
Thanks