Document about available vs explicit buffer

[ewjmulder]

    // TODO: Document decision: available() seems like a good candidate, but cannot be used in this case,
    // because AudioFloatInputStreamResampler will always return 0 (probably because trying to calculate any meaningful
    // value is quite hard given the different byte rates of the input and output streams).
    // Furthermore, available() is some kind of 'best guess' method that is not very reliable.
    // For instance, with Open microphone streams, it will show the amount of bytes for half a second as available,
    // even though in reality it's much more.

    // Anyway, there is a better option: always keep a little buffer ourselves that we can read from directly and
    // just refill in the background (other thread) when needed. That other thread may be blocking, no problem,
    // so no need to check available(), reading will be done when it's done.
    // Only downside is: no option to fill a step partly. Decision: when the custom buffer is not ready, too bad, we just take
    // only silence.
    // TODO: maybe differentiate for live / non-live? Both in buffer size / refill policy and what to do when empty / not ready.