Last time I’ve took look at Simple Direct Layer and how to get audio out of it. If SDL still feels little bit too hard to cope with I think I have solutions for you: libAO. Besides being no brainier with API libAO provides huge list of supported operating systems.
There is so much audio systems supported that you won’t be dissapointed but as much as I like everyone use Roaraudio. I don’t see it’s happening really soon (sorry roar you had your time in fame) but supporting Roaraudio  doesn’t mean that libAO is obsolete. It’s far from being obsolete. Libao supports OSS, ALSA and Pulseaudio out of the box and only problem is license is GPL 2.0+ so it’s no-go for proprietary development.

History

LibAO is developed under Xiph umbrella. Xiph is the organization who brought you Ogg/Vorbis, FLAC, Theora and currently they are hammering together next generation video codec Daala. Opus-audio codec standard is also Xiph project. LibAO rised from Xiph’s need multi-platform audio output library for Vorbis-audio codec. In this point if you don’t have any glue what I just said in last sentences I think you should take your spoon and start shovelling about Open Source audio codecs.
Becaus of the history libAO only has output mode and doesn’t use any callbacks. It doesn’t have fancy Float32 mode (as much as I understood) but that doesn’t say it’s bad thing. It works as expected you just feed bytes and after while you hear them from your speakers.

What about API

Supported outputs: Alsa, Oss, Jack, Mac OS X, Windows
License: GNU General Public license 2.0+

As said libAO API is difficult to describe since there almost ain’t NAN of it. You initialize, ask output device, put in your mode settings and start feeding data. Pulseaudio simple is almost easy as this but it’s still more difficult if you compare it to libAO. LibAO doesn’t support recording so only output and there must be a way to use another device than default but it’s not very easy to find or I was too lazy to dig it out.

So who wants to use libAO? People in hurry and don’t mind GPL-license, someone with very very tiny need of just getting audio out and people how hate bloat.

Summary: So if you hate bloat and again license doesn’t make you unhappy please use this library. Still libAO has kind of same problem that ALSA has. It’s mature, usable and ready for hardcore torturing but is it sexy? No! Is fresh? No, No! Is something that will change it API every week or hour?

After this I have to choose what to bring next. I have FFmpeg, Gstreamer and VLC in row. If you have opinion about next framework let me know.