The Bigger Picture: Visual Archives and the Smithsonian
And Action: The Ins and Outs of DVD Video Preservation
Preservation of born-digital video is one of the more challenging types when it comes to digital files. As we noted in August, the Archives worked with Smithsonian Channel programs on DVD this summer. This project helped us develop workflows we are now adopting with some born-digital video.
Video on authored DVD is complicated. If you have ever viewed the files on a computer, usually you will see an AUDIO_TS folder and a VIDEO_TS folder. The VIDEO_TS folder contains VOB, IFO, and BUP files and the AUDIO_TS folder is empty. The VOB (video object) files contain the video and audio streams, subtitles, and menus; VOB is the wrapper or container. IFOs are information files or directions that the DVD player uses and the BUP files are backups of the IFO files. The video codec itself is MPEG-2 with either linear PCM, AC-3 or DTS audio within the VOB wrapper. The Archives also has received other video containers and codecs on DVDs and external drives that include MOV, AVI, MPG, and SWF formats. Workflows are to be developed for those separately.
We have seen a wide range of playback quality with these DVDs. The videos are lossy, meaning there has been compression to get smaller file sizes, resulting in some loss of data from the original production file.
The Archives’ policy is to transfer all digital files to our server and create a copy as soon as possible after receiving them. We do this because specific media, software, and hardware can become obsolete quickly, and it also allows us to determine current preservation requirements. Just copying VOB, IFO, and BUP files directly off the authored DVD breaks the menu functionality that one sees when a DVD is launched from a player or computer. Our solution has been to create a complete disk image or ISO of the DVD. This ISO file can be mounted to a computer for viewing with appropriate player software as if it was an actual DVD with the user menus in place. This serves as our preservation master.
An access copy, which should easily play back in multiple viewers on a computer while retaining menus, was desired as well. This was the tricky part, as results were mixed when testing various software programs. Either the video menu was missing or artifacts (distortion or waves in the picture) were introduced into the video. Timecodes (running time of the video) also were corrupted.
Working with the Smithsonian's Digital Asset Management System (DAMS) team in the Office of the Chief Information Officer (OCIO), we started testing ffmpeg, which is a popular and free command-line tool for converting, streaming, and recording video and audio. We successfully have been able to create one VOB by stitching all the VOB files together and then using ffmpeg to transform that VOB file into a playable MPEG-2 with an MPEG wrapper that is supported within the enterprise DAMS used internally at the Smithsonian. Ffmpeg also retains original timecode of the authored DVD from the concatenated VOB files, in addition to any original subtitles on the disc.
While the access MPEG-2 file lacks the menu’s functionality, there is a brief screen of the menu at the beginning of playback. When asked why it is important to capture the menu the answer is the information that is displayed. In the example of the baby anteater video screenshots here, its menu provides dates and times when it was filmed (at least according to the settings of the recording device), which is not always apparent from the DVD file directories.
This workflow, though, is not the final solution. Some videos on authored DVDs that were created with a Mac have not been successfully transformed to date and more research is needed. Digital preservation always will be a moving target. As tools and software change and mature, there also is the need that procedures do the same through regular evaluation to make sure the right approaches continue to be taken with digital assets.
- Digital Video Preservation: Continuing the Conversation, The Bigger Picture blog, Smithsonian Institution Archives
- Digital Video Preservation: Further Challenges for Preserving Digital Video and Beyond, The Bigger Picture blog, Smithsonian Institution Archives
- Born Digital Video Preservation: A Final Report, Smithsonian Institution Archives
- Refining Conversion Contract Specifications: Determining Suitable Digital Video Formats for Medium-term Storage, Federal Agencies Digitzation Guidelines Initiative