Have audio backends report playback progress

**Is your feature request related to a problem? Please describe.**

If the system is somehow loaded, we could get underruns. That's because audio is send chunk by chunk (separated by the indexing marks), so as to follow playback progress.

**Describe the solution you'd like**

The audio modules should instead be able to be fed with all available chunks (that can fit the audio stack buffers), and when playback progress reaches an indexing mark, it would report it.