When it comes to streaming from a Mac people have had very little options.
Especially where something decent is required. The best two solutions were always Wirecast, and Flash Media Encoder. The former being horrible overpriced for it's performance, and latter just being rubbish over all; with it desperately needing third-party programs to even function.
So with great glee it seems Open Broadcasting Software has hard the calls of Mac users, and are finally working on something usable.
It's still an early work in progress, but it's a start and you can currently download it over at Github.
jp9000 is doing everyone on the macintosh an amazing service, I emplore you to offer support and help in the endeavour. It is after all an open project.
"Rewriting something so large from scratch is dangerous and incredibly ambitious, but we have been successful and have pulled through the worst of the worst to get to this point, it's absolutely been worth it. I've learned so much, and it's been an honor meeting some amazing programmers and becoming a part of such an awesome community. I may contribute the majority of the code, but the fact is without everyone who's been involved, this really wouldn't have been possible."
Read this before asking about features
IMPORTANT: Scene editing is not yet implemented, it's next up on the agenda. This is very important to note.
Bitmap sources are not yet implemented, also next up on the agenda as it's also pretty important.
Custom x264 settings entry has not yet been implemented.
Video device capture is in for mac (all hail palana), but because of lack of scene editing, you can't really put it in to a corner of your stream at the moment - It's still very unstable. Expect crashes, and give us crash and bug reports if possible.
Downscale sharpening shaders have not been implemented yet, so scaling down will be a little bit blurry.
Saving/loading/switching/importing/exporting scene profiles hasn't been implemented yet.
This is the 'basic' user interface, meant to be simple and easy to use for casual users, keep in mind that there are other user interfaces that are in the works, and this interface still has many improvements to be added.
Only supports OSX 10.8+.
Don't expect major support right now, this is an incomplete test build, most of our users and support people are windows users and aren't very familiar with mac, so you're on your own right now.
There are still a bazillion things down the road, most things you probably want are most likely already planned or in the works.
NOTE ABOUT CAPTURING DESKTOP SOUND
You must use 'soundflower' to capture desktop sound on mac, it's the only way right now:
Soundflower download: http://code.google.com/p/soundflower/downloads/list
If you're good with C/C++/Obj-C and want to contribute, or want to write new modules, or help implement some features you specifically want to see in sooner, let me know. (Not recommended for the inexperienced)
OBS rewrite thread: http://obsproject.com/forum/threads/obs-redux.7736/