What The Church Needs To Know About The HD Format

The HD Format is Wave of The Future
High-definition video requires a lot of data to store, which makes it difficult to record in a camera system and to work with in post-production.

Compression has become key to enabling the practical use of HD from consumer camcorders to high-end digital cinema.

Compression schemes can be divided into three categories: spatial, temporal and subsampling.

Subsampling has been around for decades and is still in use in all but the most high-end formats.

Similar to resizing a digital photo, it tricks the eye into thinking it sees more information than is actually present.

Spatial compression reduces data by comparing and eliminating redundant pixels within a single frame of video. For example, when shooting a blue sky, it is more efficient to come up with an algorithm that tells the decoder to make x number of pixels blue than to store the individual values.

This preserves each frame as a discreet piece of information, which makes editing easier. The earliest spatial formats, such as DVCProHD and HDCam used both color and spatial subsampling to further reduce the bandwidth requirements. More recent formats such as AVC-Intra and HDCam SR use advances in compression techniques and hardware to enable full resolution to be maintained.

Temporal compression works similarly to spatial compression and is often applied in conjunction with it. The difference is that temporal compression compares pixels not just in one frame, but within a group of frames. This reduces the storage and bandwidth to levels that bring HD within the realm of feasibility for the majority of users.

Formats utilizing both spatial and temporal compression have exploded in recent years and now dominate the HD landscape. HDV, the first of these formats to gain near-universal acceptance, uses MPEG-2 compression to squeeze HD onto standard DV tapes. XDCam HD also uses MPEG-2, but allows for higher data rates and more efficient variable bitrate compression to achieve higher quality.

AVCHD is a newer format that uses more efficient MPEG-4 compression to squeeze HD video into less bandwidth.The problem with these formats is that they take large amounts of computing power to edit.

As a solution, various other formats have been developed. Usually these formats will have higher bandwidth and storage requirements, but will be easier on the computer’s processor. Recently, some of these formats - such as Avid DNxHD, Apple ProRes, and Cineform - have emerged as high-enough quality to use for mastering and even recording.