In line with the Audio_out session a Audio_in session is used to
record audio frames. Like in the Audio_out session shared memory
in form of the Audio_in::Stream is used to transport the frames
from the server to the client. These frames consist of single
channel (mono) samples. An Audio_in::Packet always contains a full
period of frames.
A Audio_in server captures frames and puts them into the
Audio_in::Stream. To do so the server allocates a Audio_in::Packet
from the packet queue embedded in the Audio_in::Stream. If the queue
is already full, the server will override packets and notify the
client by submitting the 'overrun' signal. The client has to cope
with this situation, e.g., by saving packets more frequently.
A client will also receive a 'progress' signal from the server when
a new Audio_in::Packet was submitted to the packet queue.
Fixes#1644.
