[ubuntu] How to record a webinar?

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http://ubuntuforums.org – I need to record a webinar (for myself), which I attend. I tried many different ways, but nothing really got me to a satisfactory result. I have installed Jack and qjackctl, that did not the trick yet either. To record I use recordmydesktop. However, if at all, then the sound is very low, ... With Jack even the webinar stops and no sound at all, ... Ant for Firefox does not record webinars. Any hint how to record? (Hardware)