+---------------+-----------------------------------------------------------------------------------+
   |               |                              :                                                    |
   |  <--delay-->  |  <-- changeable buffer -------------------------------------------------------->  |
   |               |                              :                                                    |
   +---------------+-----------------------------------------------------------------------------------+
                    
   ^               ^                              ^                                                    ^
   | Where the     | The delay, i.e.              | somewhere here we                                  | here's where we enforce 
   | audio hw      | where the changable buffer   | have the goal                                      | the maximum buffer size,
   | read samples  | is handed to the fixed buf   |                                                    | considerably larger then the goal


Data is requested from the application only in blocks >= the reqsize, and also moved only in blocks >= the reqsize from the changeable buffer to the fixed buffer.