vlBeginTransfer, vlEndTransfer, vlGetTransferSize - begin and end
transfer on video path
int vlBeginTransfer(VLServer svr, VLPath path, int count,
int vlEndTransfer(VLServer svr, VLPath path);
int vlGetTransferSize(VLServer svr, VLPath path);
svr Specifies the video server.
path Specifies the path.
count Specifies the number of transfer descriptors in the array
passed. If count = 0 then the continuous mode transfer
operations are used. Transfers will continue using ring
buffers, if necessary, until vlEndTransfer is called.
xferDesc If count is non-zero, then xferDesc is an array of transfer
descriptors. Each element of the array can specify a discrete,
continuous, or automatic transfer. The contents of a descriptor
are described below.
vlBeginTransfer immediately begins a continuous transfer of video data on
the specified path if count is set to zero. If count is non-zero, then
vlBeginTransfer initiates a series of transfers on the specified path
using the fields of each descriptor as follows.
trigger An event to trigger the transfer on. VLTriggerImmediate means
that the transfer will start as soon as the daemon is able to
start. VLDeviceEvent is generally used to indicate an external
triggering mechanism, such as the GPI input.
delay A count of frames to wait after the trigger is received. In the
case of VLTriggerImmediate,
this may be ignored.
count The count of frames to transfer.
mode There are three current values for the mode:
means that a single transfer of count frames is executed.
means that a single transfer of undetermined length is
started, and will not end until vlEndTransfer is called.
means that every trigger received will cause a transfer of
count frames. In this case if delay plus count is greater
than the time between triggers, undetermined behavior may
The following events may be delivered once vlBeginTransfer has been
events are delivered for each frame transfer on paths which use
events are delivered to indicate an error condition preventing
vlEndTransfer ends the transfer of video data on the specified path.
vlGetTransferSize returns the number of bytes of space required for a
transfer on the server specified, using the path specified, for one frame
or field of data. For this information to be useful, all controls that
can effect the size of the data should be set before this call.
The user is responsible for multiplying the returned value by the number
of frames to get the buffer's size.
There are several controls that affect the transfer of data. See the
documentation for the particular controls of a device that affect the
data transfer, such as rate, addresses, field or frame mode, depth,
format, sizes, etc.
If successful, vlBeginTransfer and vlEndTransfer return zero. A value of
-1 indicates an error, and vlGetErrno(3v) can be called to return the
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