Full D1 vs 1/2 D1

[Sturge33]

I am capturing video from VHS and from what I've read, 1/2 D1 seems to be most people's preferred resolution. I tried capturing just a 20 second video at Full D1 and at 1/2 D1 to see how big the difference would be in file size. The Full D1 video actually ended up being 18 kb smaller than the 1/2 D1 video. They were both taken from the very beginning of the tape I'm capturing from. Shouldn't the 1/2 D1 video be smaller in file size than the Full D1 video?

[wulf109]

Resolution does not effect file size. 720x480 has about twice as many pixels as 352x480. That means fewer bits per pixel on 720x480.
As long as you can keep the average bitrate at 3000 or higher 720x480 will produce visibly sharper images even from VHS tape.

[Richard_G]

As Wulf109 says, it isn't the resolution that keeps the file size down but the bitrate. If you were to capture D1 straight to mpeg2 you would normally want to use a bitrate of around 6000 - 9000 kbs to keep the quality, at 1/2 D1 you can halve the bitrate (3000 - 4500 kbs) and the quality will be the same but the file sizes will be halved. This also means that you will have a DVD compliant frame size but be able to get around 3 hours per DVDR.

With footage taken from VHS I've gone down to 1/2 D1 at 2500 kbs and still had results that look no worse than the original.

[presto]

As long as you can keep the average bitrate at 3000 or higher 720x480 will produce visibly sharper images even from VHS tape.

to keep the quality, at 1/2 D1 you can halve the bitrate (3000 - 4500 kbs) and the quality will be the same but the file sizes will be halved.

Aren't these contradictory?

[fmctm1sw]

I think you'll find both sides to this argument here. Given the 21" TV I have that we watch TV on, I stick with 352x480 with bitrates around 3000/3500. I don't think I'd see any big difference on that little TV. Isn't the max verticle resolution of small tube TVs around 300 anyway? Maybe folks with bigger TVs would benefit from a full D1 res. I don't know since I've never had one.....

[Gazorgan]

On my standard 27" TV, I can't really tell full D1 from 1/2 D1. AVCD also looks about the same.

What I do anymore is use 1/2 D1 with 48 Khz audio. I burn that as SVCD and it plays great (it's CVD by definition). But now I can Author a DVD with zero conversion issues!

I shoot for video bitrates for 1/2D1 around 3000. This equivalent to an xSVCD bitrate of 3200 or so. Quality is excellant! And, I can easily get 1 hour on a CDR if needed, or 4-6 hours(even 8 with work) on a DVD.

I can tell the difference on my friends 42" widescreen, but then I don't have $2000 to drop on one for me.

[fmctm1sw]

What I do anymore is use 1/2 D1 with 48 Khz audio. I burn that as SVCD and it plays great (it's CVD by definition). But now I can Author a DVD with zero conversion issues!

I shoot for video bitrates for 1/2D1 around 3000. This equivalent to an xSVCD bitrate of 3200 or so. Quality is excellant! And, I can easily get 1 hour on a CDR if needed, or 4-6 hours(even 8 with work) on a DVD.

That's is exactly what I do most of the time. To a tee....

[trevlac]

I love this question ... The one about resolution, not file sizes

Here is a tasty thread at doom9 about it.

http://forum.doom9.org/showthread.php?s=&threadid=67287

I did some tests on my BT878 card. Below is a full D1 capture of a resolution chart from the Avia test DVD (available at your local store), the same capture at 368, and a full capture of the same chart from a VHS recording.

Has anyone ever tried this type of test?

http://pics.trevlac.us/img.htm?712Full.png
http://pics.trevlac.us/img.htm?368.png
http://pics.trevlac.us/img.htm?VHS712.png

The most interesting thing (to me) is that if I capture at 368 (and crop to 352), I get more resolution than cap at full and resize. VHS resolution is so low, I'm not sure this last point matters for VHS.

Trev

PS: As stated, file size is a function of bitrate. Also, resolution is not the same thing as frame size (a minor point maybe :P ).

[fmctm1sw]

Yeah, the capture res debate refuses to die. Neat pictures though. I have the same card ....

[trevlac]

Yeah, the capture res debate refuses to die. Neat pictures though. I have the same card ....

Do you then cap at 352? Anything less than 368 using the BTwincap driver seems to kick in a filter on the chip. It messes with the vertical even if you don't want to change the size in that direction.

Here is an example. Compare that to 368. Even VHS has a better vertical picture.

]http://pics.trevlac.us/img.htm?356.png