Broadly low-level audio APIs are divided into 2 categories:

1. Callback-based - every time the underlying system has a new block of audio available and/or needs to be supplied with a new block, it calls your callback, which reads input data, does whatever processing you want, and writes output data

2. Stream-based - Inputs and Outputs are represented by streams. You can read from the input stream to record and write to the output stream to play back.

Both types of API can be used for low-latency audio, but you generally introduce a buffer of latency when you need to convert between them.

Portaudio lets applications choose which API they want to use.

[0]http://www.portaudio.com/license.html

OpenAL does have a recording API so it isn't pure playback only.

But you are right in that the OpenAL scope is fairly limited. It was designed for games, particularly for rapid and frequent playback of simultaneous short sound effects. Because of this, the memory management issues you bring up are not often an issue. You load all the buffers you need at the beginning of the level and you keep reusing them without any more memory allocation/deallocation.

OpenSL ES was adopted by Android in 2.3 (API 9). However, they just recently seemed to invent yet another API, and seem to be leaving OpenSL behind.

So are all official OpenGL implementations (MESA isn't official, last I heard). Doesn't stop them from being a standard and being used, although I agree they would be better if they were open source.