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File Format Recommendations

The Northwestern University Libraries recommends certain formats be used when planning for long-term preservation of digital content and for possible submission to the digital repository. Generally, the applications used to open files and their specifications become harder to find over time, and some formats will be difficult or impossible to read in the future. The file formats with the best chance of survival have open specifications, are high quality, and are in relatively wide use. Ensuring these formats can be accessed or read in the future is key to their long-term preservation.

When considering the long term viability of your digital files, please use the recommended file formats and make sure the format is an uncompressed version, highest quality compressed version, or the final production version. Unfortunately, it's not possible to provide a single list of file formats that are appropriate for all use cases, but this list is a good starting point. Also, please exercise caution when using proprietary formats and digital rights management (DRM) software that may make viewing content difficult or impossible to access in the future. If you have any questions, please contact the Library at Your question will get routed to the appropriate staff who manage the digital repository.

Simplified Guidelines/File format recommendations:

  • Audio — Highly recommended: AIFF (.aif, .aiff) or WAV (.wav). Moderately recommended: MP3 (.mp3), AAC (.mp4, .mp4a, .aac), FLAC (.flac) or ALAC (.m4a).
  • Video — Highly recommended: Uncompressed Quicktime Movie (.mov); uncompressed AVI (.avi). Moderately recommended: MPEG-1, MPEG-2 or MPEG-4 encoded video (.avi, .mpg, .mpeg, .mov, .mkv, .mp4).
  • Virtual Reality/3D — Highly recommended: X3D (*.x3d). Please talk with a Northwestern Digital Librarian to determine best output settings and format.
  • Image - Highly recommended: Full color images @ 600dpi or higher saved as JPEG2000 Lossless (.jp2) or TIFF 24-bit, uncompressed (.tif, .tiff). Moderately recommended: lossy compressed formats limited to JPEG (.jpg, .jpeg), JPEG2000 (.jp2), TIFF (.tif, .tiff), or PNG (.png) at highest quality possible.
  • Text - Highly recommended: Open Document Text (.odt), UTF-8 Unicode text (.txt), or PDF/A (.pdf). Moderately recommended: Rich Text Format (.rtf).
  • Presentation - Highly recommended: Open Document Presentation (.odp). Moderately recommended: PDF/A (.pdf) for images only.
  • Spreadsheet - Highly recommended: Open Document Spreadsheet (.ods). Moderately recommended: Comma separated value CSV (.csv) or Tab-delimited text file (.txt).

Detailed Guidelines/Preservation Best Practices:

High probability of long-term preservation Moderate probability of long- term preservation Low probability of long-term preservation

- AIFF (PCM) (.aif, .aiff)
- WAV (PCM) (.wav)
- Broadcast WAV (PCM) (.wav, .bwav)

For music: 24 bit, 96 kHz or better

For speech: 16 bit, 44.1 kHz or better

For music:

- AIFF (PCM) (.aif, .aiff)
- WAV (PCM) (.wav)
- Free Lossless Audio Codec (.flac)
- Apple Lossless (.m4a)

For speech:

- Advance Audio Coding (.mp4, .m4a, *.aac)
- MP3 (MPEG-1/2, Layer 3) (.mp3)
- MP2 (MPEG-1 Audio Layer II) (.mp2)
128 kbps (mono),
256 kbps (stereo) or better, 44.1 kHz,
variable bit rate settings off if possible.
AIFF or WAV preferable.

- Advance Audio Coding (.mp4, .m4a, .aac) for music
- MP3 (MPEG-1/2, Layer 3) (.mp3) for music
- MP2 (MPEG-1 Audio Layer II) (.mp2) for music
- Ogg Vorbis (.ogg) AIFC (compressed) (.aifc) - NeXT SND (.snd)
- RealNetworks 'Real Audio' (.ra, .rm, *.ram)
- Windows Media Audio (.wma)
- Protected AAC (.m4p) - WAV (compressed) (.wav)
Audio (MIDI) - Standard General MIDI (.mid, .midi), original or Level 2,
Universal SysEx commands
only, instruments well documented
- Any other MIDI file not listed here
Virtual Reality/3D X3D (.x3d) VRML (.wrl, .vrml)
U3D (Universal 3D file format)
STEP (ISO 10303) (.stp .step)
IGES (NBSIR 80- 1978/ASME Y14.26M) (.igs, .iges) for basic geometry only
All other virtual reality formats not listed here

- AVI (uncompressed, motion JPEG) (.avi)
- QuickTime Movie (uncompressed, motion JPEG) (.mov)

Recommendation: Maintain original resolution of video and audio

- MPEG-1, MPEG-2 (.avi, .mpg, .mpeg, .mov)
- MPEG-4 ASP (.avi, .mkv, .mp4,)
- MPEG-4 H.264 (.avi, .mkv, .mp4, .mov,)
- Ogg Theora (.ogg)
[requires open-source decoder for Windows or Mac playback]

Standard Definition recommendations:
720x486 pixels, 2.5Mbits/second for MPEG-4; 5Mbit/second for MPEG-2. Audio 448kbit/sec, 16 bit, 44.1kHz.

High Definition recommendations:
1920x1080 pixels, 8 to 15 Mbit/s. Audio 16 bit, 44.1kHz

- 3GP (.3gp, .mp4)

- Flash Video (.flv, .f4v)

- MPEG-4 ASP (Divx, Xvid) (.avi)

- MPEG-4 H.264 (DRM protected) (.m4v, .mp4)

- RealNetworks 'Real Video' (.rv)

- Windows Media Video (.wmv) 

Image (raster) Full color @ 600dpi or higher:
- JPEG2000 Lossless (.jp2)
- TIFF 24-bit, uncompressed (.tif, .tiff)
- JPEG (.jpg, .jpeg)
- JPEG2000 lossy compressed (.jp2)
- PNG (.png)
- TIFF lossy compressed (.tif, .tiff)
- GIF (.gif)
- Macintosh Graphics (.pict)
- Photoshop document (.psd)
- All other image formats not listed here
Image (vector) - Open Document Graphics (.odg) - Scalable vector graphics (.svg) - Illustrator document (.ai)
- Photoshop document (.psd)
- All other image formats not listed here
Text - UTF-8 Unicode text (.txt)
- Open Document Text (.odt)
- Word XML (.docx)
- Rich Text Format (.rtf)
- PDF other than PDF/A (.pdf)
- Word (.doc)
- HTML (.htm, .html)
- Pages (.pages)
- All other text formats not listed here
Presentation Interactive
- Open Document Presentation (.odp)
Static (images only)
- PDF/A Animated - See video guidelines
- PDF other than PDF/A (.pdf)
- PowerPoint XML (.pptx)
- PowerPoint (.ppt)
- Keynote (.key)
- HTML (.htm, .html)
Spreadsheet - Open Document Spreadsheet (.ods) - Excel XML (.xlsx)
- Comma separated value CSV (.csv)
- Tab-delimited text file (.txt)
- Excel (.xls)
- Numbers (.numbers)

Formats to be determined: ebook, database, email, address book, compression formats (.zip, .rar), applications (.exe, .app), and many others.

Last reviewed: August 2023