Sustainability of Digital Formats: Planning for Library of Congress Collections

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Content Categories >> Still Image | Sound | Textual | Moving Image | Web Archive | Datasets | Geospatial | Generic

Moving Image >> Curator's View

The illustrative tables presented here are intended to suggest how a curator of moving image content would determine format preferences. The first table illustrates a planning matrix that would result from analyzing the significant or essential characteristics for content subcategories. The second table illustrates how this analysis of significant features would be combined with technical information about formats to produce a set of format-preference statements for the subcategories.

NOTE: This page was drafted in 2004 and has not been updated. Beginning in 2015, the Library of Congress has published its format preferences as a Recommended Formats Statement, updated annually.


Table 1: Significant characteristics of moving image content subcategories

  Description Clarity and Fidelity (picture and sound resolution) Sound field (beyond stereo) [1] Rendering expectations beyond normal [3] Special functionality required by custodians [4] Special functionality expected by end users Effect of technical protection [5]
M1 Moving image productions for theatrical distribution or specialized copies for archiving by creators or distributors. May have surround sound. Very important. Frame integrity likely to be important, extended dynamic range may be important. If surround sound, retain with minimal change If surround sound, multiple speakers Downsample, take excerpts, etc., without artifacting. Downsample, take excerpts, etc., without artifacting. Must not affect clarity.
M2 Video productions fully realized prior to dissemination via terrestrial, cable, or satellite broadcast, e.g., made-for-cable programs, TV dramas, documentaries. May be high definition, may have surround sound. Very important, retain HD if present. Frame integrity may be important. If surround sound, retain with minimal change [2] If surround sound, multiple speakers Downsample, take excerpts, etc., without artifacting. Downsample, take excerpts, etc., without artifacting. Must not affect clarity or normal rendering.
M3 Video productions fully realized prior to dissemination via videotape, DVD disk, or Internet, e.g., promotional programs, independent productions, oral histories. May be high definition, may have surround sound. Very important or important, depending on item, retain HD if present. If surround sound, may be normalized to stereo [2]   Downsample, take excerpts, etc., without artifacting.   Must not affect clarity or normal rendering.
M4 Video programs for terrestrial, cable, or satellite broadcast assembled at transmission time, e.g., scheduled newcasts, news specials, studio talk shows. May be high definition. Less important, retain HD if present.         Must not affect normal rendering.
M5 Cybercasts streamed over the Internet, other than program material covered in M3 or M4. Less important         Not important
M6 Video incidental to Web harvesting (e.g., short animations that illustrate a web page) [6] Not important          
M7 Encoding for dynamically generating animations and/or interactive programs, e.g., animated shorts for web delivery or for playback on personal computers and the animated output of CAD-CAM systems, but not deemed appropriate for "save as video." [7] Retain precision of original N/A Through specialized performance software Retain functionality of original via performance & composition software [7] Retain functionality of original via performance & composition software Must not affect functionality for end users

Notes:

1. Generally speaking, this characteristic is associated with surround sound, although it may also pertain to multi-channel audio (e.g., narration available in English and French). There is related interest in metadata that offers a map of the channels.

2. Reduction to two-loudspeaker rendering should be feasible with appropriate software. Normalization to stereo may be appropriate for content that has a more complex sound field originally but where this particular characteristic is not deemed necessary for retention. 

3. Normal rendering means playback with picture on a single screen and sound in mono or stereo through one or two speakers (or equivalent headphones). Associated software provides user control over some picture elements (brightness, hue, contrast) and over some sound elements (volume, tone, balance) and also navigation features (fast forward, go-to-segment, etc.). Normal rendering would also allow playback through software that allows sound picture and sound analysis and excerpting. Normal rendering must not be limited to specific hardware models or devices and must be feasible for current users and future users and scholars.

4. Normal functionality for custodians includes the ability to preserve digital content and provide service to users and designated communities now and decades. Thus custodians must be able to replicate the content on new media, migrate and normalize it in the face of changing technology, and disseminate it to users at a resolution consistent with network bandwidth constraints.

5. Technical protection must not prevent custodians from taking appropriate steps to preserve the digital content and make it accessible to future generations. See Notes 3 and 4.

6. In contrast, moving image files harvested from the Web through a program targeted specifically at video capture would be considered as M2 through M5.

7. Guidelines from custodians and user communities will be needed to determine when the functionality inherent in a encoded representation is an essential characteristic or when the composition should be preserved as bitmapped-image video. If saved as bitmapped video, computer-generated animations fall into categories M2 or M3.

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Table 2: Format preferences for moving image subcategories

This document was drafted in 2007 and has not been updated. The compiler of this document solicits comments from specialists in the field about some of the acceptable format options listed in the sixth column below, especially those representing relatively more proprietary encodings and wrappers. An effort has been made to limit this listing to the most stable and widely adopted types. For better or worse, these are often the "best" version in the hands of creators or distributors and works in these formats are likely offered to the Library for its collections. Presumably, the Library would wish to transcode many such offerings for preservation purposes upon arrival or shortly thereafter. As noted in Video Streams as Sources for Files, the emphasis at this Web site is US video source formats (NTSC and ATSC) and details appropriate to the non-US PAL and SECAM video systems are omitted.

  Description Preferred formats [1] Acceptable formats
  Encoding type File type, subtype Encoding type File type, subtype
M1 Moving image productions for theatrical distribution or specialized copies for archiving by creators or distributors. May have surround sound. Uncompressed, lossless compressed, may include surround sound [3]

DPX_2 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 [4]
High-quality lossy (open), may include surround sound [5] MPEG-2 (high-quality profiles) or MXF file containing MXF_GC_MPEG-2
MPEG-4_AVC high quality profiles
MPEG-4_V high quality profiles
M2 Video productions fully realized prior to dissemination via terrestrial, cable, or satellite broadcast, e.g., made-for-cable programs, TV dramas, documentaries. May be high definition, may have surround sound. [2] Uncompressed, lossless compressed, may include high definition or surround sound [3]

MXF file containing MXF_GC_UNC, MXF Generic Container Mapped to Uncompressed Images, or MXF_GC_UNC, MXF Generic Container Mapped to JPEG 2000 [4]
MJP2_FF_LL [4]
• Uncompressed or lossless compressed in other wrappers, e.g., AVI, QuickTime, WMV, etc. Comments welcome. [4]
High-quality lossy (proprietary)[5] • Compressed in wrappers like AVI, QuickTime, WMV; especially high-resolution encodings like Sorenson_4 and WMV9_PRO. Comments welcome.
High-quality lossy (open)[5] MPEG-2 (high quality profiles profiles) or MXF file containing MXF_GC_MPEG-2
MPEG-4_AVC high quality profiles
MPEG-4_V high quality profiles
Low-quality lossy [5] MPEG-2 various profiles
MPEG-4_AVC various profiles [5]
MPEG-4_V various profiles [5]
• Compressed in wrappers like AVI, QuickTime, and WMV. Comments welcome.
M3 Video productions fully realized prior to dissemination via videotape, DVD disk, or Internet, e.g., promotional programs, independent productions, oral histories. May be high definition, may have surround sound. [2] High-quality lossy (open) [5] MPEG-2 (various profiles) or MXF file containing MXF_GC_MPEG-2 with HD and AAC surround
MPEG-4_AVC
MPEG-4_V
High-quality lossy (proprietary) [5] • Compressed in wrappers like AVI, QuickTime, WMV; especially high-resolution encodings like Sorenson_4 and WMV9_PRO. Comments welcome.
   Low-quality lossy [5] MPEG-2 various profiles
MPEG-4_AVC various profiles
MPEG-4_V various profiles
• Compressed in wrappers like AVI, QuickTime, and WMV. Comments welcome.
M4 Video programs for terrestrial, cable, or satellite broadcast assembled at transmission time, e.g., scheduled newcasts, news specials, studio talk shows. Low-quality lossy (open) [5] MPEG-2 various profiles
MPEG-4_AVC various profiles
MPEG-4_V various profiles
Low-quality lossy (proprietary) [5] • Compressed in wrappers like AVI, QuickTime, and WMV. Comments welcome.
M5 Cybercasts streamed over the Internet, other than program material covered in M3 or M4. High-quality lossy (open) [5] MPEG-2 various profiles
MPEG-4_AVC various profiles
MPEG-4_V various profiles
High-quality lossy (proprietary) [5] • Compressed in wrappers like AVI, QuickTime, WMV; especially high-resolution encodings like Sorenson_3 and WMV9_PRO. Comments welcome.
    Low-quality lossy [5] MPEG-2 various profiles
MPEG-4_AVC various profiles
MPEG-4_V various profiles
• Compressed in wrappers like AVI, QuickTime, and WMV. Comments welcome.
M6 Video incidental to Web harvesting (e.g., short animations that illustrate a web page) As available • Any    
M7 Encoding for dynamically generating animations and/or interactive programs, e.g., animated shorts for web delivery or for playback on personal computers and the animated output of CAD-CAM systems, but not deemed appropriate for "save as video." [6] Computer animation, CAD-CAM animation formatsFLA, Macromedia Flash Project File; Comments welcome.
SVG_1_2, Scalable Vector Graphics, v.1.2 (animation)
SVG_1_1, Scalable Vector Graphics, v.1.1 (animation)
Comments sought regarding CAD-CAM animation formats.
Computer animation SWF, Macromedia Flash SWF File; Comments welcome
Comments sought regarding CAD-CAM animation formats.

Notes:

1. Some of the formats listed here include elements that may be employed for technological protection. If implemented, such protections may defeat preservation. Thus the assignment of preferred or acceptable status to these formats assumes that protections have not been implemented or that the Library is in a position to overcome them.

This table excludes media-dependent formats (e.g., DVD disks) as inappropriate as part of a general strategy for long-term preservation of digital content.

2. Surround sound is important to retain when it is a key element of the artist's intent (e.g. sounds intended to move around in the performance space). However, for most content, reduction to stereo is appropriate.

3. The production and management of uncompressed and losslessly compressed video is very much an evolving field, and this preference is, in fact, tentative and provisional.

4. At this writing, MXF (Media Exchange Format) and MJP2_FF are listed illustratively. Comments welcome.

5. Quality will depend upon the degree of compression and specific encoding algorithms applied to moving image content. Thus the same compressed-video formats appear in this table under both "high-quality " and "low-quality" labels; the distinction is revealed by the file's data rate, not the format. Examples of the range of choices include the Public Broadcasting Service plan to considering archiving standard definition MPEG2 files encoded at about 50 mbps, for possible re-broadcasting; the U.S. Senate recording studio consideration of high definition MPEG2 files at about 100 mbps, as masters for many types of repurposing; and the Vanderbilt University's Television News Archive's decision to create standard definition MPEG2 files encoded at about 6 mbps, as service copies for researchers to consult.

6. Guidelines from custodians and user communities will be needed to determine when the functionality inherent in a encoded representation is an essential characteristic as compared to the determination that the content can be preserved in "frozen" or flattended form as bitmapped-image video. If saved as bitmapped video, computer-generated animations fall into categories M2 or M3.

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Last Updated: 01/ 5/2017