Video

Digital video and audio capture is managed using a “codec” and a “wrapper”. The codec encodes and decodes the digital file and the wrapper collects the video, audio and metadata together in one package for access and distribution. One example is the use of a motion picture experts group (i.e., MPEG-4) video codec in the MP4 wrapper, developed by Microsoft. Video produced using this codec/wrapper uses the file name extension .mp4. While this is a simplistic explanation of formats, it is important to understand the basic foundations of digital files to effectively preserve digital data.

Lossless Compression

Video clarity is closely tied to image file size with greater picture size generally providing greater clarity. Video files are large and are often “compressed” for distribution and storage. Compressed files are also called “lossy” because some of their original digital data has been discarded to produce a smaller file, which is easier for distribution.

Digital video can be delivered via cinematic projection, television, internet streaming, mobile device and digital video disk (DVD). Any time a digital file is shared electronically, moved from one storage device to another or streamed online, the file must be compressed and decompressed. Lossy compression discards some of the original bits of data and is used to facilitate online video streaming services, for example, because less bandwidth is required for delivery to the viewer. Uncompressed video retains the original file bits producing an exact copy of the master file, but they are too large for distribution. Selecting lossless formats and sharing via processes that do not discard data, e.g., delivery of a hard drive to a digital cinema, will preserve the integrity of the original file. ZIP (.zip) is a lossless compression format for distributing digital files electronically.

Retention of the original digital data is necessary during preservation activities to provide fidelity to the artistic and technical qualities of a production. Each delivery method requires specific processing, and a key component of visual clarity is digital image compression. Selecting lossless, or uncompressed, formats preserves the original data and are preferred when quality is more important than size.