How to trim silence from audio with ffmpeg in php - php

Question

My hosting does not have ffmpeg's silenceremove filter, so I'm trying to remove the beginning and end silence of an audio file with silencedetect then cut. I'm trying to do this programmatically with php. At this point, I can't even detect the silence. I've tried:
define('UPLOAD_DIR', $_SERVER['DOCUMENT_ROOT'].'/audiofiles/');
$filein = UPLOAD_DIR . "music.ogg";
$fileout = UPLOAD_DIR . "music_no_silence.ogg";
$fileouttxt = UPLOAD_DIR . "music_log.txt";
$ffmpeg = "/usr/local/ffmpeg/bin/ffmpeg";
I first tried to put the ffmpeg command into a variable and then tried to access the output but was unable:
$output = shell_exec("$ffmpeg -i $filein -af silencedetect=n=-50dB:d=1");
echo $output;
I then tried to create a.txt log of the conversion but the .txt file doesn't show anything about the silencedetect. Furthermore, how would I be able to extract the info that I need programmatically from the .txt log in order to use it in php?
shell_exec("$ffmpeg -i $filein -af silencedetect=n=-50dB:d=1 $fileout 2> $fileouttxt");
I'm basically trying to adapt the answer at https://stackoverflow.com/a/25698675 into php
Edit: Here's kind of a hack way to do it:
define('UPLOAD_DIR', $_SERVER['DOCUMENT_ROOT'].'/audiofiles/');
$filein = UPLOAD_DIR . "music.ogg";
$fileout1 = UPLOAD_DIR . "music_out1.ogg";
$fileout2 = UPLOAD_DIR . "music_out2.ogg";
$ffmpeg = "/usr/local/ffmpeg/bin/ffmpeg";
$command = "$ffmpeg -i $filein -filter_complex silencedetect=n=-10dB:d=0.5 -y $fileout1 2>&1";
$output = array();
exec($command,$output);
$searchword1 = 'silence_end';
$endmatches = array_filter($output, function($var) use ($searchword1) {return preg_match("/\b$searchword1\b/i", $var);});
$endmatches = array_values($endmatches);
$parts1 = explode(" ",$endmatches[0]);
$a = $parts1[4];
$a = $a-.5;
$searchword2 = 'silence_start';
$startmatches = array_filter($output, function($var) use ($searchword2) {return preg_match("/\b$searchword2\b/i", $var);});
$startmatches = array_values($startmatches);
$parts2 = explode(" ",end($startmatches));
$b = $parts2[4];
$b = $b+.5;
$c = $b-$a;
exec("$ffmpeg -i $fileout1 -ss $a -t $c -y $fileout2 && rm $fileout1");

Answer 1

PHP's shell_exec returns the output written to stdout and ffmpeg writes the messages to stderr. If you want to use shell_exec you must redirect the stderr output to stdout using 2>&1.
You also need to specify at least one output file for ffmpeg, in this case /dev/null.
set_time_limit(0);
$input_file = 'music.ogg';
$cmd = "ffmpeg -i {$input_file} -af silencedetect=n=-50dB:d=1 -f null /dev/null 2>&1";
$output = shell_exec($cmd);
if (preg_match_all("/^\[silencedetect\s[^]]+\]\s([^\n]+)/m", $output, $matches)) {
var_export($matches[1]);
}
An alternative is to use proc_open and stream_get_contents.