There is a problem with mp3 conversion when using youtube plugin.
It is possible that it only affects big files.

OS: Linux Fedora 27
FRD version 0.9u4
plugin: youtube.com - 2.9.15

Settings of the youtube plugin that were used:
- Convert to Audio (MP3) ... Audio bitrate: 256 kbps
- Enable internal DASH multiplexer/merger (other checkboxes are not checked).

Steps:
1. Add url (example URL where the problem occurs: [www.youtube.com])
2. Wait for the mp4 file to get downloaded (287MB - 1 hour video)
3. Conversion starts but doesn't finish - it stops +- when mp3 file is 25-35MB large - 20-25 min of the song)
4. Error is shown in the UI "ERROR - Error starting download".

It looks like option "Extract audio" works flawlessly for the same URL ... what tool does FRD use for mp3 conversion ?

Latest errors from error log:

Fri Jul 13 22:41:12 CEST 2018 SEVERE: 
cz.vity.freerapid.plugins.exceptions.PluginImplementationException: Player js url not found
	at cz.vity.freerapid.plugins.services.youtube.YouTubeRunner.run(Unknown Source)
	at cz.vity.freerapid.plugins.webclient.AbstractFileShareService.run(AbstractFileShareService.java:102)
	at cz.vity.freerapid.core.tasks.DownloadTask.doInBackground(DownloadTask.java:98)
	at cz.vity.freerapid.core.tasks.DownloadTask.doInBackground(DownloadTask.java:42)
	at javax.swing.SwingWorker$1.call(SwingWorker.java:295)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at javax.swing.SwingWorker.run(SwingWorker.java:334)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
Fri Jul 13 22:41:51 CEST 2018 WARNING: Couldn't create fir /home/scr4bble/.FRD
Fri Jul 13 22:41:58 CEST 2018 WARNING: No Content-Disposition (filename) header in file
Fri Jul 13 22:43:23 CEST 2018 WARNING: Couldn't create fir /home/scr4bble/.FRD
Fri Jul 13 22:43:29 CEST 2018 WARNING: No Content-Disposition (filename) header in file
Fri Jul 13 22:47:11 CEST 2018 WARNING: Loading file failed - invalid HTTP return status code: 416
Fri Jul 13 22:48:15 CEST 2018 WARNING: Loading file failed - invalid HTTP return status code: 416
Fri Jul 13 22:49:19 CEST 2018 WARNING: Loading file failed - invalid HTTP return status code: 416

Btw. I might help with developing in the future if you are still looking for devs. Just drop me an email :) (vy kľudne písať česky, ja rozumieť tá jazyk)

The youtube plugin uses an MP3 encoder that is written in Java (jump3r) to convert audio to MP3. It does not always work very well as you may have noticed.

Developers are always welcome. The source code is available at [svn.wordrider.net] (username/password wordrider for read-only access). If you have any patches, you can post them. If you want to develop more, we can possibly give you a proper SVN account.