What is the "True Life" aspect ratio of Mini-DV footage on..

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The aspect ratio of mini-DV footage is 3:2 (720x480). When mini-DV
footage is being transferred via firewire to a PC, resulting in an AVI
file, does the codec automatically convert the footage to the 4:3
(640x480) aspect ratio that is native to the computer monitor? I notice
that when I do a frame-grab to a JPG file, the aspect ratio of the
resultant picture is 4:3. Also, if I play the AVI in BSPlayer, and
toggle through the various aspect ratios, "Original" (i.e. 720x480)
looks distorted, and 640x480 looks more true-to-life, which would make
sense if during the creation of the AVI file the aspect ratio was
changed to 640x480 while maintaining proportionality.

I suspect a conversion from 3:2 to 4:3 is occurring during the transfer
from camcorder to PC, but would like to hear from someone who knows
better than me.

Regards,
Jiefu

 

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"jiefu" wrote ...
> The aspect ratio of mini-DV footage is 3:2 (720x480).
> When mini-DV footage is being transferred via firewire
> to a PC, resulting in an AVI file, does the codec automatically
> convert the footage to the 4:3 (640x480) aspect ratio that is
> native to the computer monitor?
.......
> I suspect a conversion from 3:2 to 4:3 is occurring during the
> transfer from camcorder to PC, but would like to hear from
> someone who knows better than me.

Go and read the "Pixel shape" conversation.

(Hint: DV pixels are not square)

 

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MiniDV footage is intended for display on a standard tv. The aspect
ratio of a standard TV is 4:3, therefore the aspect ratio of miniDV
footage is 4:3. The pixel aspect ratio of the encoded DV footage is
not 1:1, and that is why even though the resolution aspect is not 4:3,
the displayed image is (when shown on a TV).

When captured on a computer via 1394, there is no convertion of the
data from the camera other than packaging into an AVI file format (PC).
Therefore when viewing the DV footage on a computer with standard
square pixel resolutions, the aspect of the video may not be correct
unless the player scales the video into a 4:3 window. The original
file will not be converted, but the player can do this on the fly. And
it's likely that JPG snapshots from the player will be converted as
well in this case.

 

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Fly135,
I've read several threads on this topic, and your comments are by far
the clearest and most concise of any that I've read. Thanks for
expressing in a nutshell what others seem to have such a hard time
putting into plain English.

Regards,
Jiefu

 

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Jiefu, Thanks for the kind word.

John, I can think of two possible explanations.

1) You camera is capable of recording in letter box mode and there is a
indicator in the video stream that ULead sees.
2) Somehow you inadvertently managed to change the attribute of the
clip in ULead.

I'm guessing that you just captured all the clips the same way and it
just ended up this way. I took the trouble of looking up your camera
on the Canon web site and noticed that it has a feature called "16:9
Wide Screen TV Effect". I believe that you will find that is the
source of your puzzle. You may have played with this feature and as a
result explanation "1" would apply.

 

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On 20 Jan 2005 10:59:42 -0800, "FLY135" <fly_135@hotmail.com> wrote:

>...
>When captured on a computer via 1394, there is no convertion of the
>data from the camera other than packaging into an AVI file format (PC).

This is very interesting, but I still can't determine why some of my
captures get converted and others don't.

[From my earlier thread "720x480 vs. 720x480, 4:3", to which there
were no responses]:-

Looking at the Properties of the video clips in the Library Manager,
(Ulead Video Studio V8)I see

Attributes: 24 Bits, 720 x 480, 4:3
on the non-letterboxed clips, but

Attributes: 24 Bits, 720 x 480
on the letterboxed clips.
--
John W Hall <wweexxsseessssaa@telus.net>
Cochrane, Alberta, Canada.
"Helping People Prosper in the Information Age"

 

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On 21 Jan 2005 06:42:56 -0800, "FLY135" <fly_135@hotmail.com> wrote:

>1) You camera is capable of recording in letter box mode and there is a
>indicator in the video stream that ULead sees.
>2) Somehow you inadvertently managed to change the attribute of the
>clip in ULead.
>
>I'm guessing that you just captured all the clips the same way and it
>just ended up this way.

Hi Fly, thanks for your response, and your earlier information was
helpful.

I had looked for anything like 16:9 settings, and don't think I could
have stumbled into it by accident. Also, I suspect the effect of that
would be more severe than I'm seeing. I'll do a test on that though.

Your second guess is more likely, I reckon. Except that I can't find
any way to affect that In Ulead.

These clips were shot on two tapes over two days, separate tape each
day, all with the same camera settings AFAIK. They were captured with
"split by scene" (into separate files per scene). I will check if the
differences occur on only one tape, or both.

I think I'll go back and re-capture, trying split and not, and making
careful notes of settings and results.


--
John W Hall <wweexxsseessssaa@telus.net>
Cochrane, Alberta, Canada.
"Helping People Prosper in the Information Age"