Class QueueSink

A queue sink manages a number of buffers that are organized in two queues:

• A free queue that buffers are pulled from to fill with data from the device
• An output queue that contains the filled buffers ready to be picked up by the program

To create a queue sink, use one of its constructors (QueueSink(PixelFormat, IBufferAllocator, int) or QueueSink(IEnumerable<PixelFormat>, IBufferAllocator, int)).

Pass the sink to StreamSetup(Sink, IDisplay, StreamSetupOption) or StreamSetup(Sink, StreamSetupOption) to feed images into the sink.

Usually, the sink is interacted with by registering handlers for the sink's events. The Events are raised at different significant points in the lifetime of a queue sink:

• SinkConnected occurs when a data stream is being set up from the device to the sink. The event handler is responsible for making sure there are enough buffers queued for streaming to begin.
• FramesQueued occurs whenever there are images available in the output queue.
• SinkDisconnected occurs when a previously-created data stream is stopped.

To retrieve the oldest available image from the output queue, call PopOutputBuffer() or TryPopOutputBuffer(out ImageBuffer). The returned image buffer is owned by the program. If the program no longer needs the image buffer, Dispose() must be called it to return the image buffer to the sink's free queue.

A program does not necessarily have to requeue all image buffers immediately; it can choose keep references to the a number of them in its own data structures. However, please note that if there are no buffers in the free queue when the device tries to deliver a frame, the frame will be dropped. Use StreamStatistics to find out whether a buffer underrun occurred.

This operation is only valid while the sink is connected to a device in a data stream.

The buffers are retrieved in order they were received from the video capture device; the oldest image is returned first.

After a successfull call, the program owns the image buffer through the ImageBuffer reference. The image buffer object must be disposed to put the image buffer into the sink's free queue for later reuse.

This operation is only valid while the sink is connected to a device in a data stream.

The buffers are retrieved in order they were received from the video capture device; the oldest image is returned first.

After a successfull call, the program owns the image buffer through the ImageBuffer reference. The image buffer object must be disposed to put the image buffer into the sink's free queue for later reuse.

The event handler usually calls PopOutputBuffer() to get access to the filled image buffers.

If this callback function performs a lengthy operation, it is recommended to regularly check IsCancelRequested to determine whether the data stream is being stopped.

The function is executed on dedicated thread managed by the sink.

When the data stream to the sink is stopped, the StreamStop() call will wait until this event handler returns. This can quickly lead to a deadlock, if code in the event handler performs an operation that unconditionally requires activity on the thread that called StreamStop().

The event handler can abort the creation of the data stream by setting AbortConnect to true.

MinBuffersRequired indicates the minimum number of buffers required for the data stream to operate. If the event handler does not allocate any buffers, the sink will automatically allocate the minimum number of buffers required.

The function is executed on the thread that calls StreamSetup(Sink, StreamSetupOption).

The function is executed on the thread that calls StreamStop().