Sustainability of Digital Formats
 Planning for Library of Congress Collections

Device-independent digital video for end-users

General
For content as delivered to end-users or consumers, generally compressed (see section on professional applications for uncompressed and lossless compressed content). Clarity and fidelity characteristics (bitstream encoding) should be used as the primary consideration; choice of file formats as secondary. Note that this page deals only with device-independent digital video and not video in physical formats intended for consumer equipment, e.g., DVDs.

Bitstream encoding for video (relates to clarity and fidelity)

• Larger picture size preferred over smaller picture size. Picture size is expressed as horizontal lines and number of samples per line, or as horizontal and vertical pixel counts.

• Content from high definition sources preferred over content from standard definition, assuming picture size is equal or greater.

• Higher bit rate (often expressed as kilobits or megabits per second) preferred over lower for same compression scheme.

• Surround sound encoding only necessary if essential to creator's intent. In other cases, stereo or monaural sound is preferred.

File type

• Not copy-protected rather than copy-protected

• Relatively complete descriptive and technical metadata rather than minimal

• Acceptable file formats, in order of preference. Note that for audio streams in MPEG-2 and -4 formats, AAC is preferred to other audio encodings.

  - MPEG-2

  - MPEG-4_AVC

  - MPEG-4_V

  - MPEG-1

  - Compressed in wrappers like AVI, QuickTime, WMV, etc.

Encoded animations and moving image interactives

General

• This category includes files that contain encoding for dynamically generating animations and/or moving image interactive programs, e.g., animated shorts for web delivery or for playback on personal computers.

  - Such animations may be produced by specialized software, e.g., Macromedia Flash, or by certain kinds of Computer Aided Design or Computer Aided Manufacturing (CAD-CAM) systems, especially for three-dimensional drawings that may be rotated to simulate viewing from various points of view.

  - For certain classes of works, e.g., non-interactive short animations, the Library generally does not retain dynamic encoding data and will often prefer to receive these works saved as bitmapped video, in which case the preferences for device-independent digital video for end-users or professional moving image applications apply. However, when dynamic generation and/or video interactivity are essential characteristics of a work, then the file containing the encoding is preferred.

  - Animations that consist of only a few frames, e.g., an animated GIF, are covered under the heading of Still Images.

  - Computer games form a category of their own; at the moment, these are not collected by the Library of Congress and they are not treated at this Web site.

• The bitstream encoding in a variety of formats is based on similar principles and approaches. The primary preference considerations, therefore, have to do with the openness or standardization of a format (disclosure) and/or with how widely adopted it is.

File type

• Acceptable formats

  - FLA, Macromedia Flash Project File

  - SWF, Macromedia Flash SWF File

  - SVG_1_1, Scalable Vector Graphics, Version 1.1 (animation)

  - SVG_1_2, Scalable Vector Graphics, Version 1.2 (animation)

Formats for professional moving image applications

General
For content as used in professional applications, e.g., for production, post-production, distribution, or archiving of moving image content in device-independent digital form. Clarity and fidelity characteristics (bitstream encoding) should be used as the primary consideration; choice of file formats as secondary.

Bitstream encoding for video (relates to clarity and fidelity)

• Larger picture size preferred over smaller picture size. Picture size is expressed as horizontal lines and number of samples per line, or as horizontal and vertical pixel counts.

• Content from high definition sources preferred over content from standard definition, assuming picture size is equal or greater.

• Encodings that maintain frame integrity preferred over formats that use temporal compression.

• Uncompressed or lossless compressed preferred over lossy compressed.

• Higher bit rate (often expressed as megabits per second) preferred over lower for same lossy compression scheme.

• Extended dynamic range (scene brightnesses) preferred over "normal" dynamic range for such items as Digital Cinema or scanned motion picture film.

• Surround sound encoding only necessary if essential to creator's intent. In other cases, stereo or monaural sound is preferred.

File type

• Not copy-protected rather than copy-protected

• Relatively complete descriptive and technical metadata rather than minimal

• The formats in this category are emerging, and this list of acceptable formats for uncompressed or lossless compressed data should be treated as provisional.

  - DPX_2 with picture information together with suitable format for sound information

  - DCDM_1_0 (tentative)

  - MXF file containing MXF_GC_UNC, MXF Generic Container Mapped to Uncompressed Images, or MXF_GC_UNC, MXF Generic Container Mapped to JPEG 2000

  - MJP2_FF_LL, Motion JPEG 2000 File with Lossless Encoding

  - Uncompressed or lossless compressed in other wrappers, e.g., AVI, QuickTime, WMV, etc.

• Acceptable file formats for compressed video, in order of preference. Note that for audio streams in MPEG-2 and -4 formats, AAC is preferred to other audio encodings.

  - MXF file containing MXF_GC_MPEG-2, MXF File with MPEG-2 Video Stream, higher-quality profiles and levels preferred

  - MPEG-2, higher-quality profiles and levels preferred

  - MPEG-4_AVC, higher-quality profiles and levels preferred

  - MPEG-4_V, higher-quality profiles and levels preferred

  - MPEG-1

  - Compressed in wrappers like AVI, QuickTime, WMV, etc. High-resolution encodings like Sorenson_4 (HDTV), Sorenson_3, and WMV9_PRO preferred.