Interleave, preload duration: 500 ms. What is that?

[synnchan]

I just made a duplicate out of a video of mine using VirtualDub. I simply selected "Direct stream copy > Save as AVI" and didn't touch anything else. This is the original video:



And this is the duplicate:



I sort of understand that the duplicate has "Writing library: VirtualDub build 32842/release" on the General tab since that's the program I used to make it. But what's up with that "Interleave, preload duration: 500ms" on the Audio tab? I don't understand what is that for.

[jagabo]

Interleave is the size of the audio chunks. Preload is the amount of audio that appears before the video starts. In VirtualDub see Audio -> Interleave...

[hello_hello]

This is the way Microsoft explains it:

https://msdn.microsoft.com/en-us/library/windows/desktop/dd318180%28v=vs.85%29.aspx
dwInitialFrames
Specifies the initial frame for interleaved files. Noninterleaved files should specify zero. If you are creating interleaved files, specify the number of frames in the file prior to the initial frame of the AVI sequence in this member.
To give the audio driver enough audio to work with, the audio data in an interleaved file must be skewed from the video data. Typically, the audio data should be moved forward enough frames to allow approximately 0.75 seconds of audio data to be preloaded. The dwInitialRecords member should be set to the number of frames the audio is skewed. Also set the same value for the dwInitialFrames member of the AVISTREAMHEADER structure in the audio stream header.

Interleaved files have a bit of video, followed by a bit of audio, then a bit of video etc etc. If they didn't navigating would be slow/impossible.
I assume different programs use different preload values by default. It's still exactly the same audio and video though (assuming you used direct stream copy for both) and VirtualDub has always defaulted to 500ms as far as I can recall. If media info doesn't show a preload duration, there probably isn't one.

VirtualDub's Audio/Interleaving menu lets you change it to whatever you like. You can also change the way the audio is interleaved with the video (for constant bitrate audio). The greater the value, the less overhead and the smaller the file size, although the difference isn't terribly much. Change the value to 2 or more frames though, and the output file size will reduce a little. AutoGK, a program well known for creating AVIs compatible with any sort of AVI capable DVD player, uses an interleave of 2 frames. I don't know how high you could go before you'd start having problems. I think it'd effect the speed at which you could navigate more than actual playback though.