Src

This is the most simple base class for audio sources that only requires subclasses to implement a set of simple functions:

* `open()` :Open the device. * `prepare()` :Configure the device with the specified format. * `read()` :Read samples from the device. * `reset()` :Unblock reads and flush the device. * `delay()` :Get the number of samples in the device but not yet read. * `unprepare()` :Undo operations done by prepare. * `close()` :Close the device.

All scheduling of samples and timestamps is done in this base class together with BaseSrc using a default implementation of a RingBuffer that uses threads.