File formats for creating new audio and video material are often closely associated with the type of equipment used. For example, most cameras will only support a few digital video file formats.
If your organisation has the opportunity to purchase new equipment for recording, they should examine what file formats or codecs are supported and if they are suitable for the intended use and longevity of the recording. Consider:
- Is the file being created/received in the course of official business and might it be needed to be accessed for use or to provide evidence of business? ie is it a corporate record?
- Is high audio or video quality required for this project? (the quality achieved will be dependent on the equipment used to record as well as the format chosen)
- Is the file being created expressly to meet a short term need? Or does it have significant business value (e.g. intellectual or financial)? Might it have long term cultural or other value? Your organisation’s retention and disposal authority will assist you in determining the value of the file and how long it may need to be retained.
Even if the file is a corporate record, if it only needs to be kept for a very short period of time your organisation should use the format and codec which is most suitable for the aims of the project and compatible with editing software to be used. The processing power and storage space you have available may also impact on your decision.
Many of the MPEG file formats (e.g. mp3) which are standard definition, affordable and widely available may be used if the recordings are only required in the short term and fast delivery (e.g. over the web) is the goal. However, they use lossy compression and are not considered to be of sufficient quality for preservation.
Long term or archival, or where quality is paramount
If the audio or video file:
- will require long term or archival retention or
- needs to be of optimal quality
your organisation should try to use a suitable format of as high a quality as possible for the creating of the preservation ‘master’ file. Duplicating copies and reference copies can then be made at a quality fit for purpose.
Formats should meet as many of the identified Criteria for choosing formats for preservation purposes as possible. However, sometimes these may need to be balanced with the resources and equipment available.
Only linear uncompressed codecs or mathematically reversible lossless codecs should be used for preservation. No compression is ideal, but the files may take up considerable storage space (particularly video files). Your organisation will also need the processing power to be able to open and view the files and do error checking etc.
If your organisation needs to use existing equipment and is therefore tied to the file formats associated with these, they should consider creating a preservation ‘master’ by copying to a suitable format. Copying to a higher quality format will not increase the quality of the original recording. However, the original recording should never be copied to a format of lesser quality when the aim is to create a preservation master (e.g. do not copy a Digital BetaCam recording produced professionally onto a DVD to create a preservation master). The aim should be to preserve as much quality of content as possible from the original recording.
Widely recognised and accepted formats for preservation purposes for audio are WAV or BWF. These are uncompressed and generally use the lossless Linear Pulse Code Modulation (LPCM) codec. They retain as much information as possible from the recording source. Most digital audio capture software can record into these formats. BWF has the advantage over its predecessor WAV of significant metadata capacity and has widely adopted standards for metadata exchange and interoperability.
FLAC is a suitable format for digital preservation as it is stable, free and open source and employs lossless compression. The National Archives of Australia converts a number of other audio files (including WAV) to FLAC during the process of normalisation for storage in their digital archive. If considering this format for business use, however, it is important to note that it is not widely supported by the audio industry.
If the image is to be optimised, lossless methods should be used and information regarding the optimisation should be saved with the audio file separately from the preservation master.
For more information and issues to consider when choosing an audio file format, including recommendations in relation to different methods of delivery, refer to the JISC infokit: Digital File Formats.
There is no consensus to date among the archival community as to which file format or codec should be used for the creation of preservation masters for digital video. Therefore, State Records cannot make specific recommendations regarding what particular creation formats should be used.
Your organisation should assess potential formats against the Criteria for choosing formats for preservation purposes.
National Film and Sound Archive (NFSA), Digital Media Preservation: Video [unpublished]
JISC Digital Media, Choosing a Digital Audio File Format, 3 February 2009
Published January 2009 / Revised May 2016 (references only)