“The origin of AVI and its codec”
■ What is AVI?
When it comes to Real and QuickTime, AVI is the next choice. AVI is a format provided by Microsoft for storing multimedia data. The official name is “Audio Video Interleaving”, and it is characterized by a structure in which image data and audio data are interlaced alternately based on a format called RIFF (the name “Audio Video Interleaving “is also here. I come from).
■ AVI Background
As I mentioned a bit last time, in September 1991, Microsoft released a package called “MME (MultiMedia Extention)” as an extension to Windows 3.0 for handling multimedia. However, there was no format that could handle video in this (this is probably the first reason Apple’s QuickTime lags behind).
This feature is not covered by Windows 3.1, which appeared in April 1992, and is finally realized by an expansion pack called “Video for Windows (VFW)” which appeared in November of the same year. The AVI format is compatible with this VFW. However, at this point, QuickTime has a sizable stake, and with the advent of “QuickTime for Windows”, the ground has been formed that “QuickTime is good for Windows.” Of course, QuickTime is not all-purpose, and VFW-compatible products have been prominent from the beginning, for example in video capture, but still it took a long time for VFW to catch up with the initial lag.
Well, that AVI format. The most important feature is that you do not define the codec yourself. In other words, it is an “everything” format. Figure 1 is a very simple summary of the AVI structure defined in the AVI 1.0 format, but the one that is correctly defined in the AVI format is “RIFF Header / AVI Header (avih) / MOV Header (in all three types of” movh ) “, the stream header and MOV snippet just indicate that” stream format definition is entered here “and” actual data is entered here. “After all, in the case of the first VFW, both the audio and the video were uncompressed.
If you really create it with this, an AVI file will be created with an internal structure as shown in Fig. 2. If it is a 30fps video, it can be handled as a beautiful video if you play it from your head in a format that alternately alternates a still image every 1/30 of a second and 1/30 of a second of audio.
Also, there are no hard stories like this method and coding, so even a poorly performing PC at the time could be fully used. However, these methods make the file size too large. For example, assuming a 320 x 240 pixel, 24-bit color, 22KHz / 8-bit stereo display, the image alone is 6.6MB per second and the audio is 1.3MB, for a total of approximately 8 MB. Even if you use the full capacity of the CD-ROM (650MB), it is a terrifying size that can only record 81 seconds, which is absolutely useless.
■ Various codecs
Therefore, we will combine several codecs with the AVI format and try to compress the video using it. A codec called “Cinepak” developed by Radius of the United States was used relatively from the beginning, and now Compression Technologies has taken care of this and released a product called “Cinepak Pro” (Cinepak itself is released. Already included as standard in Windows from the beginning).
Then a codec called “Indeo” developed by Intel became quite popular. There are many popular versions of this Indeo, such as 3.2 / 4.1 / 5.1, but the problem is that they are not compatible with each other. That being said, in most environments it is common for all codecs to be included as standard, and for normal use it shouldn’t be a problem. By the way, Intel withdrew from the development of “Indeo 5.1” in the end, and Ligos Corporation is currently developing and supporting it. The latter is sold under the name “Indeo XP”.
Microsoft itself also developed the codec. That is what is called “Microsoft Video 1”, which is limited to 8 or 16 bit colors, but the compression ratio was not very high.
It can be subtle to include this in the codec, but the AVI format has a file size limit of 2GB or less. This 2GB was a size that I would not exceed in the 1990s, but after 2000 it is a size that easily exceeds when capturing TV etc., especially when using a PC for absent recording etc. It was a big problem doing it. A method called AVI Reference Format was designed to solve this problem.
