Screencast with both mic and system sounds at the same time

I'd like to make a screencast that records both mic (audio input) and system sounds (audio output) at the same time. For example, so that I can capture a screencast while talking to someone on Skype and capture both sides of the conversation. How can I do this? (I'm using Natty if it matters.)

So far I have tried Kazam, RecordMyDesktop and Tibesti. (Tibesti explicitly has this feature but it doesn't seem to work. Kazam has existing enhancement requests for this feature.)

Please provide complete instructions/options, like those given for running RecordMyDesktop from the command line in this generic screencasting answer.

Solution 1:

Found a solution. Been pulling my hair out forever searching for an answer that isn't needlessly complicated.

Install and use Open Broadcaster Software (aka OBS Studio). Seriously, that's it.

You can follow the Linux installation instructions or just use the Snap store.

You can configure OBS to simultaneously record:

• screen (XSHM screen capture)
• mic (PulseAudio audio input capture)
• system sounds (PulseAudio audio output capture)

Solution 2:

Look for a way to combine sound channels instead of looking for multirecording screencast app. How to mix voice and audio on Ubuntu (archive.org copy) describes how to do it with PulseAudio. This tutorial seems to be based on Weekend Project: Record From Skype Calls and Other Apps on Linux (linux.com). IIRC there are also similar in spirit tricks for JACK)