QuickTime 4 Reference

Working With Video Fields

QuickTime 2.5 introduced support for working directly with fields of interlaced video, such as those created by some motion JPEG compressors.

Because video processing applications sometimes need to perform operations on individual fields (for example, reversing them or combining one field of a frame with a field from another frame), QuickTime now provides a method for accessing the individual fields without having to decompress them first. Previously such operations required decompressing each frame, copying the appropriate fields, and then recompressing. This was a time consuming process that could result in a loss of image quality due to the decompression and recompression of the video data.

Three new functions (ImageFieldSequenceBegin , ImageFieldSequenceExtractCombine , and ImageFieldSequenceEnd ) allow an application to request that field operations be performed directly on the compressed data. These functions accept one or two compressed images as input and create a single compressed image on output.

The Apple Component Video and Motion JPEG compressors support image field functions in QuickTime 2.5 and later. See the description of the ImageFieldSequenceBegin , ImageFieldSequenceExtractCombine , and ImageFieldSequenceEnd functions for information on how to process image fields in your application. See Image Compressor Components for information on incorporating support for these functions in other compressors.