Difference between type 1 and type 2 dv-avi files

Factors that can limit an AVI's size may include the filesystem, and the type of AVI file itself.

With the latest implementations of the FAT filesystem i.e. DOS, Windows 3.x, Windows 95 (pre-SR2) (no longer commonly used), maximum file size is 2GB.

With the latest implementations of the FAT32 filesystem i.e. Win95 SR2, Win98, Win2k, WinXp maximum file size is 4GB.

Here are your commonly associated 2GB/4GB filesize limitations, however, implementations of AVI may also be further limited by things like:

AVI 1.0

Microsoft's Video for windows has some hardwired limitations that impose a maximum video filesize of 1-2GB depending on the version of the RIFF parser code in the MCIAVI driver.

Surprisingly enough, much video software was written to these standards and this is where much of today's incompatibility stems from.

The AVI file header is 32-bits in length. As a result there is a 4GB limitation in its file size.

With the latest implementations of NTFS maximum filesize is limited only by the volume size which is currently rated to be 2 Terabytes+ is maximum size.

Even with NTFS as a filesystem, which most of us are now running, you may have software applications, drivers, and plugins that only will function up to the 4GB limitation of a native AVI or worse yet, only up to the 1-2GB limited sizes imposed by early versions of AVI implementations (Video for Windows).

OpenDML file format extensions (AVI-compatible). These extensions were written to over come AVI filesizes limitations of 1GB / 2GB / 4GB and to incorporate specialized AVI information into the AVI file's chunks.

Some AVI chunk size / extension header progressions: (chunks, or data structures, are the portions of the AVI file that software drivers and applications deal with. these are the units that all of this limit stuff is about. Extension headers are the part of the AVI file that has information flagged if there is something non-standard about the AVI file. For example, it if is larger that 1GB in size.)

Limited to 1GB MCIAVI
Extensions for >1GB AVIX
Entensions for >4GB AVI_INDEX as well as other meta index structures

AVI 2.0 (OpenDML 1.02)

The most significant change with AVI 2.0 (now implemented in MS' Direct Show filters) is the ability to concatenate multiple AVI chunks through the use of 64-bit data types.

Theoretically, this would allow 18 Billion GB's. While not technically unlimited, it certainly far exceeds what most need for their DV projects.

Additionally, AVI 2.0 is superior in that it uses a meta index file structure at the beginning of the file as opposed to AVI 1.0, which uses an index at the end of a file, therefore AVI 2.0 has significant "Seeking" advantages- a must for large AVI files

Most professional video software companies have adopted the use of AVI 2.0 format and OpenDML 1.02 file format extensions.

But what these standards really means is that there is a set of guidelines available if companies choose to use them. It may not always be a good idea or even a cost effective choice to fully utilize all extensions in OpenDML. i.e. StormEdit.

Sources for this thread came from documents like:






Lots of this information was copied from a thread in canopus forums, thanks to Chas.


Some of this is repeated, but it also may add information for peoples interest.

In the beginning, there was Video for Windows (VfW) and the data-wrapping file format AVI.
Video for Windows AVIs are often referred to as "AVI 1.0" AVI files.
Video for Windows AVIs were originally limited to 1 GB maximum size, but the size was later extended to 2 GB.

FAT (FAT16) was the filesystem used at the time.
FAT has 2GB maximum file size, and a 2GB maximum volume size (in NT you could format a FAT volume from 2GB up to 4GB with 64KB clusters, which can be problematic).

Circa Windows 95, ActiveMovie was introduced. ActiveMovie still used AVI. ActiveMovie later morphed into DirectShow. DirectShow is often referred to as "AVI 2.0"
At the same time, FAT32 was introduced.
FAT32 has a 4GB maximum file size, and a 127GB (Win9x) or 2TB (WinME, practical limit due to partition table) maximum volume size.

Meanwhile, there's NTFS, used by various versions in NT, 2000, and XP.
NTFS has a current practical limit file size and volume size of about 32TB.

Matrox and some others proposed an extension to AVI 1.0 called OpenDML, which was later implemented in AVI 2.0. This extension allowed AVIs to be larger than 2GB.

Canopus had its own extension of AVI 1.0, used in its applications, called Reference AVIs. This allowed a single AVI up to 4 GB, and multiple "reference" data files, allowing the total content to be over 4 GB.

So, a particular AVI file can be one of four types - Video for Windows aka "AVI 1.0" or DirectShow aka "AVI 2.0"
It's worth noting here that it is possible to create a "partially backward-compatible AVI 2.0" file, but the ability for VfW to access the AVI content is limited to the first 1, 2 or 4GB of the AVI, depending on the method the program uses to access it.

And the filesystem the AVI is stored on can be one of three types - FAT (FAT16), FAT32, or NTFS

This gives us this for maximum AVI sizes by AVI type and filesystem.

And then comes the further confusion. When DV came onto the scene, Microsoft defined two "types" of DV AVI files. This was because AVIs traditionally held two streams - the video stream and the audio stream. That's why you see a lot of interleaving references for AVIs - that determines how the audio and video data are arranged in the file so they can be accessed in sync. The DV format datastream, however, includes both audio and video multiplexed together.

Thus, two methods for storing DV data in AVIs (aka DV AVIs) were defined. The logic is there, but the naming makes it confusing, as it is opposite of the AVI 1.0/2.0 referencing.

"Type 1 DV AVIs" are DirectShow AVIs with the DV datastream in the vids stream. There is no decoded audio track.

"Type 2 DV AVIs" are Video for Windows AVIs with the DV datastream in the vids stream and a copy of the decoded audio in the auds stream. The copy of the audio allows traditional Video for Windows applications to decode the audio properly for playback and manipulation. However, this can lead to problems, as described further.

Audio troubles with Type 2 DV AVIs...
Because the audio exists both in the DV datastream in the vids stream of the AVI, and in the auds stream of the AVI, any changes to the audio need to be made in both the DV datastream and the audio in the auds stream. This would ensure that the audio is correct regardless of whether the audio is being decoded from the DV datastream stored in the vids stream, or simply being pulled from the audio in the auds stream.

However, programs that are not "DV AVI aware" would read the AVI as a normal AVI, assume the audio only exists in the auds stream, and therefore modify the audio in the auds stream, without modifying the audio in the DV datastream. This leads to discrepancy between the audio tracks. Playback of the AVI from an application that pulls audio from the auds stream (traditional AVI playback) could play entirely different audio from a DV AVI aware application that decode both audio and video from the DV datastream.
This is why in "the old days" sometimes you'd get a Type 1 DV AVI that played back with "wrong" audio in one application, but "right" audio in another - a bit of an "audio split-personality" problem.

3-hour limit of Canopus Reference AVIs
Since the AVI 1.0 maximum safe AVI file size is 2 GB, and the audio is being stored in Canopus Reference AVIs, there is approximately a 3 hour limit, assuming 48 kHz 16-bit stereo audio.

Copied in it's entirety from The Grass Valley (Canopus) forum, written by Brandon.


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