Yes, you can run RPAN software and OBS simultaneously, which are basically the same thing. If you wanna get real fancy, you can stream to something like Restream.io and that'll pipe out to YouTube, Facebook, Twitch all at once.
Just an FYI, sound flower isn’t receiving updates anymore but the team that made it moved onto a project called blackhole which is similar but allows for more ins and outs.
A paid option is loopback, which I like a lot, but it’s always worth trying the free options first.
The biggest issue with doing multiplatform steaming including RPAN is because RPAN has a Portrait orientation, on other platforms it might look weird or get stretched. (Eg - Streaming to Mixcloud and RPAN via Restream.io - RPAN is fine but Mixcloud is unusably stretched)
RPAN Studio is a hacked up version of OBS. currently OBS dosnt have a android port.
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you might try a rtmp app. like https://play.google.com/store/apps/details?id=com.wmspanel.larix_broadcaster&hl=en&gl=US
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as for getting your key... i have no idea how to
I haven't tried it, but it should be doable. You'd need to use a multi streaming website like restream.io that supports adding a custom RTMP channel. I know restream.io charges a monthly fee for for that custom channel though.
Yes, if you have a cable that splits the stereo out from your Macbook into 2 mono 1/4 inch plugs, then you can run that into the line inputs on the 4i4.
Example cable: https://smile.amazon.com/Tisino-Stereo-Y-Splitter-Cable-Breakout/dp/B07K58VX13