Record from Fedora via ffpmeg

13 April 2018 0

I’m playing around a web radio (for your info http://www.radiocittaperta.it, I’m also a speaker on Sunday) and what I’m trying to achieve is something that:

Create podcast for every shows, given the start and stop hour
Enable the speaker to manually start and stop a recording of the show
Enable the speaker to choose if overwrite the automatic record or not
Upload to the radio website
Create the page with the podcast

Those are quite complicated task to be done for a single IT resource, but Rome wasn’t built in a day. This post is about recording the audio streaming from the input line of the attached sound card, using a webpage to start-stop the record. First of all the radio has two computer with Fedora, they are configured as twins, just for redundancy. In the apache installation I have also installed a wordpress base installation, this gives me the functionalities of a CMS (user access, lost password, plugin management) in order to focus only on the requirments. I have created a wordpress plugin with a simple frontend button:

Start --> Stop

The behaviour follow this path https://trac.ffmpeg.org/wiki/PHP :

php start a record using ffmpeg in background
the pid of the process is saved in the database
on client side (javascript in the browser) an ajax request check if the process is still alive
stop button kills process using pid number (“kill -9 <pid#>”)

There are several pain points to take into account when using this approach: I started with arecord command, and pipe with lame library to save mp3 files, but seems that arecord could run only once per-resource (resource=sound card) and it also has a problem that I don’t know why: it’s stops after 1h 33m (ref. http://stackoverflow.com/questions/42457839/recording-with-arecord-stops-after-1h-33m-under-fedora-23) , so I switched to ffmpeg. Apache user could not been able to use audio. This is a limitation on most of the distro, I had to add apache user to the groups:

audio,pulse,pulse-access and I’ve added also video groups (don’t know if it’s necessary)

command is:

usermod -a -G video,audio,pulse,pulse-access apache

Another pain point on Fedora was SELinux. SELinux is an utility enabled by default, to manage security policy. There are several ways to work around this: investigate and set the perfect policy for folders (a lot of them are shared-memory folders), set the SELinux to be more permissive, disable SELinux. I don’t want to tell you the perfect solution, I’ve disabled it, but I don’t want you to do so, it’s a security related situation and a recovery after a security disaster is something that you really don’t want. The ffmpeg wrapper class I wrote is

<?php

include_once 'Executer.php';

/**
 * Description of FfmpegWrapper
 * * @author mbarsocchi */ class FfmpegWrapper {

    public function startRecord($mountpoint = null, $name, $timeToRun = null) {
        $timeStringToRun = "";
        $filename = $name . ".mp3";
        if ($timeToRun != null) {
            $timeStringToRun = "-t " . $timeToRun;
        } $command = "/usr/bin/ffmpeg -y -f pulse -i alsa_input.usb-Focusrite_Scarlett_Solo_USB-00.analog-stereo -loglevel fatal " . $timeStringToRun . " -c:a libmp3lame -b:a 192k " . dirname(__FILE__) . DIRECTORY_SEPARATOR . "ripped" . DIRECTORY_SEPARATOR . $filename . " </dev/null";
        $exec = new Executer();
        $exec->execute($command, true);
        $res['retcode'] = $exec->getRetCode();
        $res['output'] = $exec->getOutput();
        $res['pid'] = $exec->getPid();
        return $res;
    }

    public function stopRecord($pid) {
        $exec = new Executer();
        $exec->stopPid($pid);
        $res['retcode'] = $exec->getRetCode();
        $res['output'] = $exec->getOutput();
        return $res;
    }

}

Executer is a support class that wraps the shell_exec command. This class is also capable of getting background=true or background=false flag. When background=true is setted, the pid of the process is saved into DB with some additional information, in my case the additional infos are the name of the mp3 recorded. To stop the recording, I’ve used a brutally Kill -9 <pid>. I know I can redirect std-in in a file and use it as a file-socket to send the [q] command to ffmpeg (ffmpeg is an interactive tool, so you can send command while working, q is for “quit”). You can also choose a more elegant solution, I use this because I don’t want to mess around with left files… and stuff like this. On the page ajax call an endpoint to retrieve the runnig process, if there is a live process, the page has the button STOP with a async call to an endpoint that calls:

FfmpegWrapper:: stopRecord(<pid>)

If not, the button is START. This solution works very well for my needs, and hope this post helps you in similar solution.

MiroAdmin

ffmpeg

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