Planning so that your files will survive for a long time is tricky in general, and video is one of its trickiest areas. When even the designers of HTML5 can’t agree on a video format, what are the odds that your family’s or club’s movies will still be viewable in ten or twenty years? Even at the Library of Congress, there’s considerable uncertainty about digital video preservation strategies, and even big movie studios are at risk of not preserving their now all-digital movies.
Just figuring out what format you have is confusing. There are two things you have to know: the format of the file as a whole, called the “container,” and the way the bits represent the video, called the “encoding.” These are largely independent of each other, and the specifications for each can have multiple options. The same format may be referred to by different names, and different formats may be called by the same name.
Usually you create a video from a camera, and it probably doesn’t give you a lot of format options. If you process it with a video editor, you have more choices about the final format. The file suffix tells you what the container format is supposed to be but not what encoding was used. If it’s .MOV, you have a QuickTime container. If it’s .MP4, you have an MP4 container — which is not synonymous with MPEG-4, but rather with MPEG-4 Part 14. Both are MPEG-4 compliant but not at all compatible with each other.
It’s common to refer incorrectly to other MPEG-4 container files, including audio-only files, as MP4. If it’s not a Part 14 container, it shouldn’t be called MP4. On the other hand, its being a legitimate MP4 file tells you nothing about what encoding it uses, so not all “MP4″ files are compatible with each other; likewise for QuickTime files.
Videos produced by current cameras and software usually will use the H.264 encoding, aka MPEG-4 Part 10. You may also run into MPEG-4 Part 2, which is based on H.263. If you have a strong preference for open-source, you may want to go with the Theora codec. The win is available source code and (hopefully) a lack of patent encumbrances, but the risk is that less software supports it. Preservation is always a matter of placing bets. If you use Theora, it should be in an Ogg container, not an MP4 container; the latter combination is technically MPEG-4 compliant, as a “private stream,” but may not be supported in the long term.
An older container format, Audio Video Interleave or AVI, still has strong support. It dates all the way back to Windows 3.1. Its Full Frame encoding option lets you store uncompressed video.
Microsoft’s current entry is Advanced Systems Format (ASF), often in combination with Windows Media Video (WMV) encoding. It’s widely supported but tends to be Windows-specific, so it may not be the best choice for long-term preservation.
Most video encodings are compressed, since they take a lot of space even by modern standards, and usually the compression is lossy (i.e., it isn’t possible to recover the original data without some loss of accuracy). There are ways to get uncompressed or lossless compressed encoding, but here we’re getting into esoteric areas which I’d best not touch.
The video encoding isn’t the whole story. An encoding such as H.264 is only a video encoding, and even if you’re a silent movie fan like me, you probably like sound in a lot of your movies. The audio encoding that goes with H.264 is usually MPEG-4 Part 3 Advanced Audio Encoding, known for short as AAC, but this isn’t required. If it’s something else you could have preservation issues.
As I said, it’s a mess. I’m far from an expert in this area, but this article should give you an idea of the issues to look for.
Suggestions: Current advice varies a lot. Popular options today include a QuickTime (.MOV) or MPEG-4 Part 14 (.MP4) container with H.264 video and AAC audio if you want to go with software popularity, or Ogg with Theora and Vorbis if you value openness more. The older AVI is hardly dead. Pay attention to the encoding, not just the container format. Stay tuned for future developments and be prepared to migrate to new formats.
- Whither digital video preservation? (Library of Congress)
- Sustainability of digital formats: Format descriptions for moving images (Library of Congress) This hasn’t been kept up to date very well, and the exclusion of Theora is conspicuous, but it lists a lot of formats.
- Video File Formats: What and when to use.
- Preserving digital video (Disruptive Library Technology Jester)