DSPreRollStream

Reads data prior to playback.

Synopsis

int32 DSPreRollStream (Item msgItem, DSRequestMsgPtr reqMsg, DSStreamCBPtr streamCBPtr)

Description

Sends a message to the DataStreamer telling it to fill the buffers for a specific stream. DSPreRollStream() loads the DataStreamer buffers with data chunks from the specified stream so that they can be immediately accessed by subscribers.

DSPreRollStream() does not expect the specified stream to be running. It is normally called to fill the buffers for a stream before it is started.

DSPreRollStream() sets the members of the message data structure required to fill the data buffers. (The message is the DSRequestMsg identified by reqMsg.) If a message is specified, DSPreRollStream() sends the message and returns immediately. However, if no message is specified (if reqMsg is NULL), DSPreRollStream() creates a message, sends it to the DataStreamer, and waits until the message has been received before returning.

Arguments

msgItem: Item of the request message.

reqMsg: Pointer to the DSRequestMsg message that is formatted and sent to the DataStreamer. A value of NULL forces creation of an internal DSRequestMsg message and synchronous operation.

streamCBPtr: Pointer to the stream context block.

Messages

The members of reqMsg are set to the following values:

whatToDo: kDSOpPreRollStream

Return Value

Value: Error Condition

0: None

These values are returned if the DataStreamer encounters an error while processing the message request:

kDSInvalidDSRequest: Invalid message (whatToDo set to invalid value)

kDSNoReplyPortErr: Could not locate item of the reply port

-1: Could not locate pointer to msgItem

(Portfolio error code): SendMsg() or WaitPort() failed

The DataStreamer checks the validity of messages only if message checking is enabled when the DataStreamer is compiled (if the VALIDATE_REQUEST_CODE symbol is enabled).

See "Error Messages" in the 3DO Portfolio Reference Manual for a listing of error messages returned by SendMsg() and WaitPort().

Associated Files

DataStreamLib.h