Keepalive packets may be inserted at any point in a Kate stream
where a data packet may be inserted (eg, after all headers, and
before the end packet).
Keepalive packets are meant to help seeking code by placing packets
at regular intervals so a seeking program can keep track of the
granulepos without having to seek too much.
It is not mandatory to use keepalive packets, but their use may
improve seeking performance when a Kate stream with few events
is multiplexed with high bandwidth streams.
This packet is exactly one byte long, and consists of its packet
type, 0x01.