Digital video

Digital video is increasingly popular as a medium for documenting research projects. This can refer to the entire project or individual components, such as various surveys, experiments, processing tasks, and interviews.

A common issue with digital video in its raw format is that data files can be very large. Like digital images and audio files, digital video files contain several important characteristics that affect the file size and quality, such as image resolution, color depth, and compression.

Below, we list several file formats, but there are many other formats that may be used. Contact your local research data supportOpens in a new tab for advice on which file formats are appropriate for long-term preservation and sharing of the type of research data you are working with.

Important characteristics

Digital cameras and software often have preset values for different features, but these settings may vary, as what is standard for one camera model is not necessarily the same for another. The characteristics of a video file that should be preserved in its original form when sharing or long-term preserving the file include:

• File length and size (e.g., 6min 23s/185MB).
• Frames per second (fps) (e.g., 25 for PAL or 30 for NTSC). Frame rate describes the number of frames per second captured or displayed by the file. A higher frame rate results in smoother video, but also larger file size.
• Frame size/resolution (e.g., 720 x 576 pixels). Frame size and resolution describe the physical width and height of the video image, determining the level of detail captured.
• Bitrate for image and audio (kbps). Bitrate (BR) for audio and video streams. Bitrate is a value composed of image size, the number of bits per image, and frame rate. It defines the speed of data transfer between devices or how the data are processed over time. Video software often offers preset bitrate values, but variable bitrate options are also available to adjust values depending on image complexity. Bitrate is also a value for the compression of audio and video streams; a lower bitrate means a more compressed file.
• Audio frequency (kHz).
• Color depth (CD). The more bits, the more nuanced a color can be rendered.
• Number of audio channels (e.g., stereo).
• Accompanying metadata and documentation.

As with other formats, destructive (lossy) compression of video and audio streams leads to loss of data. If compression is necessary, lossless compression should be used whenever possible, as this preserves the “master file” quality that other files can be based on.

Before converting a video file, check it against the available documentation. The video should have the specified length (minutes and seconds), and its key characteristics should be properly documented. This ensures the file is complete and avoids any unexpected degradation during conversion.

What to preserve?

How to determine what to preserve depends largely on how the digital video was created. As previously mentioned, many of the tools used to create videos have limitations regarding quality and file types. It is essential to evaluate the limitations of the recording tool compared to the project requirements. Strive for a video of high enough quality to function for long-term preservation, such as choosing the correct file format. This applies especially to the original file, but also to any compressed versions created from the original.

It is not always possible to store completely uncompressed video files but remember that once you switch to a lower quality format, you cannot go back to improve the data or quality. This makes it even more crucial to choose a suitable file format to save or convert video files to.

Recommended file formats for sharing and long-term storage

• Lossless AVI (.avi)
• Audio Video Interleave (.avi)
• Matroska (.mkv)
• MXF (.mxf)
• Motion JPEG 2000 (.mj2, .mjp2)
• MPEG-1, MPEG-2 (.mpg, .mpeg, …)
• MPEG-4 H.264 (.mp4)

The MPEG formats use destructive (lossy) compression, which should be avoided when creating video files, but if the material was created in these formats, the files can be shared and easily reused by other researchers. There are also MPEG formats that are lossless.