The digital preservation of audiovisual (AV) data is a complex area where progress has been prevented by a lack of agreement around the choice of preservation formats, and an uncontrolled development of new formats and encoding methods. However, with the information DANS provides on preferred formats/containers of audiovisual files, we hope to inform depositors about the formats DANS considers best for long-term sustainability and accessibility of audiovisual data.
Apart from usual criteria DANS uses to decide upon whether an AV-format/container is preferred or not (e.g. openness, support and robustness), for AV-material also the criteria of ‘media-related- functionality’ is taken into account. Ideally, the format/container should support time-code, subtitles and metadata.
When it comes to audiovisual file formats there is a lot of technical terminology. This section tries to clarify the terms often used when the community talks about the curation of audiovisual material.
A container format or wrapper is a type of file format that contains various types of data into a single file, e.g. audio and videobitstreams as well as additional information like subtitles and metadata. Also, a wrapper/container can store the different types of codec that are necessary to unpack/decode the data.
Codec stands for (en)coder/decoder or compression/decompression. It is the method by which a video or audio bitstream is encoded for transmission and decoded for use. The software used to playback audio or video files must have the right codecs within their library in order to play the media files. Without an appropriate codec an encoded bitstream cannot be played. The codec also implies the type of compression (“lossy” or “lossless”, see below) that have/will occur. For long-term archiving the use of lossless compression is preferred in most cases, despite data storage concerns.
File formats and codecs may be either proprietary or free, unpublished or open. Nonetheless, for archiving purposes, free and open files formats and codecs are preferred and strongly recommended.
- MXF (.mxf)
- Matroska (.mkv)
- MPEG-4 (.mp4, .m4a, .m4v, …)
- MPEG-2 (.mpg, .mpeg, .m2v, .mpg2, …)
- AVI (.avi)
- QuickTime (.mov, .qt)