A BBuffer
references a chunk of shared memory where media data can be
passed between applications and nodes. The control header for these
buffers is passed through the use of a safer IPC mechanism, but the
actual data these headers represent typically require a high data rate,
and for the sake of maximizing performance, shared memory is the method
by which the buffers are managed.
BBuffers
originate at some
BBufferProducer,
which has a
BBufferGroup
that acts as a source of
BBuffers (see
BBufferConsumer::SetOutputBuffersFor()).
BBuffers are sent through all
participating nodes, possibly being sent down a long chain—much
like a bucket brigade—until finally the node arrives at a node that
chooses not to pass along the
BBuffer
any further, at which the buffer's
Recycle()
function is called to return the buffer to the
BBufferGroup's
store, where it gets reused by another batch of data.
An application or custom node can set up
BBuffers that reference a
specific area of memory, such as a low-level driver buffer, a
BBitmap, or
a BDirectWindow's
area of a frame buffer. This ability can provide for
great optimization by avoiding unnecessary copy operations.
The BSmallBuffer
class, derived from
BBuffer, is used for very small
buffers; they don't go in
BBufferGroups,
and get handled specially to optimize performance.
BBuffer
should never be subclassed, since they're mostly owned and
managed by the Media Server. Even if you create your own
BBuffer, once
you've called
BBufferConsumer::SetOutputBuffersFor(),
the "same" buffer received back by your
BBufferConsumer
may actually be another instance of the
BBuffer class.
