QuickTime Streaming

Sequence of Events

When QuickTime is asked to provide a packetizer, it selects the packetizer based on the media type, data format, and other characteristics, such as whether a matrix transformation is in use. It selects the packetizer best able to handle the media and track characteristics by examining the packetizer's public resource.

Once a packetizer has been selected, it is opened. It is then asked to preflight the media, to verify that it can actually packetize the desired media data. If the packetizer indicates that it can handle the media, it is initialized. The packetizer then receives a series of set-up calls required to prepare it for operation. These calls deliver information such as the media time scale and the packet builder to use for output.

Once set-up is complete, the packetizer receives a series of calls with sample data. If the packetizer can process the data immediately, it does so; otherwise it returns a flag that indicates it is still processing the data. In the latter case, the packetizer's Idle function is called perodically until the packetizer has completed its processing. When it is ready, the packetizer creates packets by making calls to a packet builder component.

The packetizer is then called again with more sample data. This continues until all the media data has been packetized.

At any time in this process, the packetizer can be asked to return information, or to flush its input buffer, or to reset itself and prepare for a new sequence.