What is AVI (Audio Video Interleaved)?

AVI (Audio Video Interleave) is an audio and video container format published by Microsoft Corporation in 1992.

What is the AVI File Extension?

The AVI file was defined by Microsoft in 1992 for the purpose of enhancing video technology for the Windows operating system. It was later developed with the format extensions of the Matrox company’s OpenDML group.

AVI files are a unique format of RIFF files, which is a general-purpose format for the exchange of multimedia data defined by Microsoft and IBM.

In fact, RIFF is a clone of the IFF format that was invented in 1984 by Electronic Arts for Deluxe Paint on the AMIGA platform.

IFF quickly developed itself as an exchange standard on this platform. When Electronics Arts decided to switch to the PC platform, it continued to use the IFF format along with it.

Although this extension format is not officially defined, it is supported by Microsoft and is called version 2.0.

Most of the time, when VfW (Video for Windows) is expressed, this format is known to be an AVI/.avi extension.

Codecs of this format were developed as drivers for ACM (Audio Compression Manager) and VCM (Video Compression Manager). Some other architectures, including DirectShow and Windows Media, can use this.

Microsoft released Windows 1.0 for Video for Windows 3.1 in November 1992, followed by Video for Windows 1.1. Additionally, there are several versions of Video for Windows 1.1, such as 1.1e, identified by a letter in alphabetical order.

While Microsoft was planning to replace it with ActiveMovie for VfW, it also created a 32-bit version of VfW for Windows 95.

This version also included 32-bit codec versions such as Cinepak, and other video DLLs for Windows 95 were also defined as 32-bit.

Also, Windows NT 3.5, 3.51, and 4.0 versions included a Video for NT for Windows. Because the hardware device drivers are very different in these two systems, it is unknown how much of this code is shared between the 95 and NT versions of Windows.

ActiveMovie 1.0 and DirectShow are 32-bit versions of VfW for both Windows 95 and NT. ActiveMovie was created under the codename Quartz, but the first beta versions were known as Quartz.

ActiveMovie 1.0 was included in Internet Explorer 3.x/4.x for early versions of Windows 9x that support disks configured in FAT 32 but can be downloaded and installed as an additional package on Windows 95.

ActiveMovie 1.0 did not wholly replace VfW but did not have any video capture mechanism. Therefore, some capture programs continue to use Video capture drivers for Windows.

ActiveMovie 1.0 was a 32-bit software component that could run in NT User Mode as well as Windows 95, but it was released mainly as DirectShow in version 2.0.

How Does AVI Format Work?

This video format allows storing and defining a video data stream and multiple audio streams simultaneously. The structure of these streams is not a type of this format and is interpreted by an external program called a codec.

The AVI file can be in any format, such as audio and video, and so it is considered a container format.

In order for all streams to be reproduced simultaneously, they must be stored at intervals. That way, each piece of the file has enough information to play several frames along with the corresponding sound.

This format supports multiple audio data streams. The support of this format means it can practically contain multiple soundtracks in various languages.

These files are divided into different parts, and each chunk is associated with an identifier called the FourCC tag.

The first track is called a title, and its role includes meta-information about the file, such as the size of the image and its rate in frames per second.

The second track contains interlaced audio and video streams and can optionally be a third track that acts as a directory for the rest of the tracks.

How to Open Audio Video Interleaved?

To open or play an AVI file, you need a video player that can interpret this format, the video codec to interpret the video stream, and the audio codec to interpret the audio stream.

The FourCC tag allows you to define the codec required to interpret an audio or video stream, and each codec is associated with the set of tags it can generate.

In this way, the video player can select and process the corresponding codec without user intervention. After the player reads parts of the video file over and over, it separates each of the audio and video streams added to the file.

Each of these streams is stored in a memory buffer after being allocated and transferred to the corresponding codec.

The video codec returns another buffer containing each of the frames to play. The audio codec returns another buffer with the digital audio sample to be played.

With this information, the player only needs to synchronize the frames and audio and play them at the proper speed.

On the macOS operating system, it is possible to play these files as long as the codecs used are installed by Quicktime directly or via plug-ins.

Other programs allow you to open these files correctly on systems such as Windows, macOS, and Linux.