This event reports the buffer status for network streams (NBC) back to the
application, providing a way to measure if the stream delivers data fast
enough. This enables the application to slow down the stream playback to
get the buffers filling more quickly. (This is only a sample application of
the event.)
The event reports all vital data like fill percentage, remaining buffer in
seconds and discontinuity, separately for audio and video, whether the nbc
layer is actually buffering, the operation type (put or get) and also if the
buffering is enabled at all.
In essence, it's the output you get from nbc if you run xine-lib in
verbose mode on the console, but in raw data.