QuickTime 3 Reference
A video output component receives QuickTime video data and delivers data to a video output device for display. If the incoming data is in a format that the video output device can display directly, the video output component can simply send the data to the video output device. If the incoming data cannot be displayed directly, the video output component must use a transfer codec or decompressor component to convert the data to a format that the video output device can display.
If a video output device cannot directly display 32-bit RGB data or data in one of the other supported QuickTime pixel formats, the developers of the device are strongly encouraged to provide a transfer codec that accepts data in one of the supported QuickTime pixel formats (preferably 32-bit RGB) and converts it to data that can be displayed on the device. When this transfer codec is available, any QuickTime video can be displayed on the video output device: the Image Compression Manager can convert any QuickTime images to a supported QuickTime pixel format and then invoke the transfer codec to display the result.
If any special decompressors, such as a transfer codec, are needed for a video output device, the decompressors are included in the definitions of the component's display modes, as described in "Display Modes" . How transfer codecs work is described in "Codec Components." How hardware developers can develop a transfer codec for their device is described in "Creating a Transfer Codec for a Video Output Component" .
Some video output devices do not accept pixels as input. For example, there are devices that display JPEG data directly. For these devices, a video output component can send the appropriate data directly, or it can invoke a compressor component to convert data in a pixel format to the appropriate data.