File size vs. quality in digital preservation

why 500MB for an hour of videotape is not enough

When archivists used to text-based formats like PDF/A are introduced to video preservation, file sizes are a shock. A 1-hour video file at 1GB seems huge compared to document files, but in the world of audiovisual preservation, 500MB is not enough to be considered a proper archival master.

Understanding the relationship between file size, compression and quality is key to making informed decisions about digital preservation.

How file size reflects Quality

The size of a digital file is determined by its resolution, bit depth, frame rate, compression and whether it keeps all the original data (lossless) or throws some away (lossy). Many archivists unfamiliar with AV materials assume because a document can be preserved in a compact format, the same applies to audio and video. But the nature of visual and auditory media means higher data rates are required to maintain integrity.

Typical file sizes for 1 hour of Archival content

Lossy vs. Lossless: why it matters

Many preservation mistakes come from using highly compressed formats, such as MP4 (H.264) or .mp3, which dramatically reduce file sizes but permanently discard visual and audio information. While such formats are acceptable for access copies, they are not suitable for long-term preservation because data loss is irreversible.

For example:

• A one-hour mp4 (H.264) SD video file at 1GB lacks significant details and introduces compression artifacts
• The same content stored as FFV1 (lossless SD video) at 35GB retains every bit of visual and audio data.

Similarly, audio stored as mp3 at 128kbps will sound significantly degraded compared to a BWF (Broadcast WAV) at 24-bit/96kHz.

Film scanning: why 4K DPX can be 2TB

Film, due to its analog nature, is best preserved at high resolutions. Scanning a 16mm film reel to 4K DPX can result in 2 TB per hour, a staggering size for those used to digital documents. However, this resolution ensures the preservation of every grain, color variation, and frame detail for future generations.

Many organizations, pressed for storage space, opt for compressed formats like ProRes or H.264, unaware that this permanently limits future restoration or remastering efforts.

Can everything be Lossless? A practical approach

While master copies should be preserved in lossless formats, not all historical content may require the highest quality. A documentary recorded off-air on VHS in the 1980s may not need a 10-bit v210 uncompressed video file, but the original magnetic master tape must be digitized with as much fidelity as possible before it degrades beyond recovery.

Decisions should be made based on:

• The historical value of the content
• The likelihood of future re-use and restoration
• Available storage capacity vs. expected longevity of the archive
• Performing tests to verify the best possible balance between quality and file size

One key rule: Always digitize at the highest reasonable quality first, as there will likely not be a second chance. Many legacy formats, especially magnetic tapes, are deteriorating, and playback equipment will be unavailable.

Final thoughts: the price of doing it right

A poorly digitized file cannot be restored to its original quality. Once lost, detail is gone forever. While storage concerns are valid, modern infrastructure allows for cost-effective archival solutions, especially for institutions preserving culturally significant works.

Archivists should approach audiovisual preservation with the same care as traditional documents, recognizing that file size is not an inconvenience, but a necessity for accuracy and authenticity. Digital preservation is an investment, ensuring that future generations can experience historical content as close to its original form as possible.

If there’s only one chance to do it right – do it well.

NextArchive expert team

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