Type-1 vs. Type-2 DV AVI Files
(source: 2002-12-14 FROM http://msdn.microsoft.com/library/default.asp?url=/library/en-us/directshow_sp1/htm/type1vstype2dvfiles.asp )
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DV cameras produce interleaved audio-video; each frame of video also contains the audio information. If you save DV data to an AVI file, you have a choice: 

Store the interleaved data as one stream in the AVI file. This is known as a type-1 file. 
Split the interleaved data into separate audio and video streams. This is known as a type-2 file. 
For video capture, where maximum throughput is crucial, it is better to use a type-1 file, because type-2 files carry redundant audio data. (The video stream still has the audio data. The audio is simply hidden by labeling the stream as video.) Also, writing a type-2 file requires some additional processor time to split the interleaved stream.

On the other hand, type-1 files are less efficient for real-time editing. The application must extract the audio from the interleaved stream, make the edits, and interleave the data again. Also, the type-1 format is not compatible with Microsoft® Video for Windows® (VFW). DirectShow can handle both types of files.