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Old 3rd August 2002, 09:22   #1  |  Link
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Join Date: Oct 2001
Location: Germany
Posts: 2,665
*** F.A.Q. ***

Q1: What's the difference between DV type-1 and DV type-2?

A1: AVI files can contain different video and audio streams. The native interleaved DV data produced by camcorders is stored in a type-1 AVI file with stream type ivas.
If the native data is split into separate audio (auds) and video (vids) streams, then we have a type-2 AVI. In this case the vids stream still contains the audio interleaved, thus the filesize is a little bigger.
Video-for-Windows (VfW) applications like VirtualDub don't work with type-1 files. You can either convert to type-2 or use AviSynth and its DirectShowSource command to open the video. In the latter case process the audio separately.

Q2: Progressive or interlaced?

A2: Most camcorders support interlaced only. If your target format doesn't support interlaced video (e.g. DivX, MPEG1), then you have to deinterlace, which costs time and quality. In case of MPEG2, which supports interlaced video, you can still go the progressive way, because you need lower bitrate for the same quality, or if you turn it the other way round: the quality will be better for the same filesize. The reason why people use interlaced is the smoother motion on a TV set, and they likely have enough bitrate because they create DVDs, not SVCDs...

Q3: How do I properly resize a DV video?

DV Aspect Ratio

A 720x576 (PAL) captured DV file has an aspect ratio of 1.25. You want to watch your video on a 4:3 (= 1.33) screen, so all you have to do is resize it to 640x480, which has the correct aspect ratio of 4:3 (640/480 = 1.33), right?


The above would be correct if the DV pixels were square, but unfortunately they are rectangular, which results in a deviation of about 9.4% according to what I have measured. To make sure I don't tell you anything wrong I filmed a square sheet of paper and measured widths and heights on my TFT screen.

The square sheet of paper was 12.6cm x 13.9cm on my screen, so the width/height ratio was 0.906. That means, if you want to get a video having a standard width of 640 pixels and a height divisible by 16, you have the choice:

1. You can crop 32 pixels, 16 from each side and resize to 640x480.
AVS sample script:

2. You can resize to 640x464.
AVS sample script:

As a result circles look like circles, not elliptic on computer monitors, because computer monitors have a pixel aspect ratio of 1:1. TV screens don't have square pixels (e.g. for PAL the ratio is about 1:1.1). I do not recommend to produce the video for pixel aspect ratios other than 1. Maybe your video card adjusts for the pixel aspect ratio, otherwise let the player do the proper resizing.

Note: If you have a camcorder which supports 16:9, then resize your 16:9 DV video to 640x352.

Q4: Where do I get technical information about DV?

A4: Look here: http://www.adamwilt.com (thanks to Ookami for providing the link).
Another interesting link: http://www.shortcourses.com/video/chapter01.htm

Last edited by bb; 17th April 2003 at 06:22.
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