Sorenson Video 1 (SVQ1) makes me sentimental. It had a lot to do with why I started multimedia hacking. Strange that it all seems so simple now.
SVQ1 is a stark contrast to our last subject, Cinepak. SVQ1 does not store its codebooks in the encoded video bitstream. Rather, the codebooks are a hardwired characteristic of the coding scheme. That’s actually a really good thing considering that the algorithm is a hierarchical multistage vector quantizer.
Cinepak is a true classic among video codecs. It saw considerable use in the early days of FMV as it was easily encapsulated in both AVI and QuickTime files, the prevailing container formats in the early days of PC multimedia. It was also the standard FMV format on early CD-based consoles such as the Sega Saturn and Atari Jaguar.
Someone was asking me about vector quantizer codecs recently. Sure, Wikipedia has the obligatory article. To its credit, the article is actually halfway useful these days (I seem to recall that it used to be a lot more impenetrable). It doesn’t help that the concept is identified by 2 terms that, by themselves, sound somewhat intimidating: ‘vector’ and ‘quantization’.
Anyway, he asked the right person about VQ codecs because I happen to love VQ codecs and can go on for days about them. In fact, I might do just that. I’ll start with a post about the theory and then describe specific examples in separate posts.
This article is maintained in Wiki format at http://wiki.multimedia.cx/index.php?title=Frame_Types.
Ultimately, encoded video data needs to be decoded to 2-dimensional arrays of pixel values and presented to the user (or perhaps transcoded to a different format). All of these frames look complete to the user. But the frames often can not stand by themselves. They usually need information from other frames in order to make their presentation complete.
Let’s talk basic video frame terminology. First, there is the intraframe. This is also known as a keyframe. An intraframe is one that can stand on its own. It requires no other frames. It carries with it all the information needed to be decoded.