Comparing Formats for Video Digitization | The Signal: Digital Preservation
FADGI format comparison projects. The Audio-Visual Working Group within the Federal Agencies Digitization Guidelines Initiative recently posted a comparison of a few selected digital file formats for consideration when reformatting videotapes. We sometimes call these target formats: they are the output format that you reformat to.
This video-oriented activity runs in parallel with an effort in the Still Image Working Group to compare target formats suitable for the digitization of historical and cultural materials that can be reproduced as still images, such as books and periodicals, maps and photographic prints and negatives. Meanwhile, there is a third activity pertaining to preservation strategies for born-digital video, as described in a blog that will run on this site tomorrow (link to come). The findings and reports from all three efforts are linked from this page.
Comparing video formats for reformatting. The focus for this project was the reformatting of videotapes with preservation in mind, and it was led by Courtney Egan, an Audio-Video Preservation Specialist at the National Archives. Like its still-image parallel, the for-reformatting video comparison used matrix-based tables to compare forty-odd features that are relevant to preservation planning, grouped under the following general headings:
* Sustainability Factors
* Cost Factors
* System Implementation Factors (Full Lifecycle)
* Settings and Capabilities (Quality and Functionality Factors)
The online report offers separate comparisons of file wrappers and video-signal encodings. As explained in the report’s narrative section, the term wrapper is “often used by digital content specialists to name a file format that encapsulates its constituent bitstreams and includes metadata that describes the content within. A wrapper provides a way to store and, at a high level, structure the data; it usually provides a mechanism to store technical and descriptive information (metadata) about the bitstream as well.” The report compares the following wrappers: AVI, QuickTime (MOV), Matroska, MXF and the MPEG ad hoc wrapper.
In contrast, the report tells us, an encoding “defines the way the picture and sound data is structured at the lowest level (i.e., will the data be RGB or YUV, what is the chroma subsampling?). The encoding also determines how much data will be captured: in abstract terms, what the sampling rate will be and how much information will be captured at each sample and in video-specific terms, what the frame rate will be and what will the bit depth be at each pixel or macropixel.” The report compares the following encodings: Uncompressed 4:2:2, JPEG 2000 lossless, ffv1, and MPEG-2 encoding.