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sequestrian
03-06-2003, 04:44 PM
does anyone know what the quality would be like if I transfered an avi to a dv camera via firewire?

dvornik
03-06-2003, 05:29 PM
http://www.videoguys.com/firewireq&a.htm

"DV in = DV out"
Very informative site BTW.

CgFX
03-08-2003, 07:45 AM
NTSC DV is colorspace compressed (4:1:1) versus the more familiar MPEG2 lossy compression. This means that its data rate requirements are reduced by sampling the color at 1/4 the resolution that it samples the brightness.

This is much less noticeable and higher quality (IMHO) compared to the content changing, lossy MPEG2 compression used for DVD-Video.

This link may interest you as it discusses the impact of using AVI.

http://home.insightbb.com/~george/codec/HiQ_photo_montages/hi_quality_photo_montages.html

This link may interest those in a great technical discussion of image sampling in various colorspaces.

http://visarts.ucsd.edu/grad/lab/dv-craigb.html

jussing
03-09-2003, 12:02 PM
Hi there! :)

To answer sequestrian's question, if you transfer a DV file over firewire, there is no loss at all, compared to the "master" DV file. It's a bit by bit transfer.

However, continuing the discussion at hand, DV also uses lossy compression, and DVD MPEG2 can look much, much better than what's remotely possible with DV.

You can easily SEE comression artifacts in a DV recording. You can also see comression artifacts in an MPEG2-stream, but only if it's poorly compressed.

And CgFX, the site you link to also specifically says

"The key to maintaining higher quality MPEG2 output is to NOT convert to a DV AVI file first"

Meaning, DV AVI really sucks compared to a good MPEG2-stream...

Cheers,
- jonas

CgFX
03-09-2003, 03:17 PM
jussing is not so wrong.

DV is compressed by way of its colorspace and you will not see content based artifacts that we are all used to with jpeg/mpeg/mpeg2.

While I agree that a good 10 Mbit MPEG2 DVD-Video stream can look pretty damn amazing, its visual artifiacts are still visable and different from DV's.

DV's quality issues stem from sampling the color at a lower rate.

Another way of looking at it is with black and white video DV is full bandwidth, uncompressed video at 720x480. Only the color information is reduced which is done at sample time on a per scanline basis. The is no frame to frame relationship with DV as there is with the per frame lossy compressed and inter-frame delta compressed MPEG2.

CgFX
03-09-2003, 03:21 PM
Originally posted by jussing
And CgFX, the site you link to also specifically says



Meaning, DV AVI really sucks compared to a good MPEG2-stream...

Cheers,
- jonas

If you would read the whole article and not just skim you might realize the point was about the affects of using AVI with Premiere as an in between step and not DV.

jussing
03-09-2003, 05:52 PM
Hi again.

Remember, keep it at a friendy level. :)

I did in fact read the article, and my point is still valid, IMO. The reason for not using DV as an inbetween step is simply that it can't live up to the potential of MPEG2. (not that I think MPEG2 is the perfect format, though)

About the color-samling, we've agreed there from the start.

All I'm saying is, there's MORE compression to it than that, and that IS lossy. I know it sucks, but that's life... :shrug:

And we also agree there's no frame-to-frame relationsship in DV's compression, unlike, for instance, MPEG and MPEG2. DV is more like MJPEG, plus the colorsampling thing.

-After all, DV has a compression rate of 5:1. -Which, needless to say, would be impossible to reach with only color-sampling compression of 4:1.

There's some more stuffhere (http://www.learndynamicmedia.com/articles/compression/introMJPEG.html). (look for "MJPEG, DV and MPEG").

Cheers,
- Jonas

dvornik
03-09-2003, 06:26 PM
sequestrian's question (before this one) was about transferring his portfolio video from PC to VHS. He does not have any cards or bridges or anything. All he has is a dualhesd videocard, Quadro4 or something. I think in his situation outputting it to DV tape and then copying to VHS makes most sense. What do you think?

jussing
03-10-2003, 05:17 AM
Yes, transferring DV to VHS like that would definately to the job nicely.

-But if it's a Quadro4, maybe there's a good TV out? If there is, he won't have to go over DV tape, he can just play the DV file (or whatever format or codec he chooses) and record it directly to VHS.

(I just know some video cards' TV out look bad, leaving a black border around the picture, and making all sorts of refresh rate problems...)

Cheers, :wavey:
- Jonas

CgFX
03-10-2003, 03:05 PM
There is intra-frame compression with DV/DVCAM/DVCPro, although it is based on a different algorithm and at a very low compression ratio.

What I can't figure out at all is why you think 10 Mbit/s DVD-Video content can be soooo much better than 25 Mbit/s DV video which uses a lower compression ratio and no inter-frame techniques?

Why is it now the format of choice for ENG and SDTV production compared to using MPEG2 @10 to 25 Mbit/s devices?

Tellerve
03-10-2003, 03:43 PM
On a somewhat related note, is there any quality difference from pulling video from a DV camera onto a hard drive with firewire as opposed to USB? Or is it just a lot slower (obviously thinking usb 1.1 not 2.0 here).

Thanks,

Tellerve

jussing
03-10-2003, 03:51 PM
Hi again,

I'm glad we got the objective facts straight. ;)

Regarding DV vs. MPEG2:

1. Subjectivity

Good MPEG2 compression requires cumbersome, manual tweaking (from what I know - I've never done it myself).

Yes, there are sucky, lousy, bad DVD's out there that are worse than had they been compressed with DV, but there are also some that kick the breath out of anything DV can match.

This is not something I say based on numbers or facts, but merely my conclusion after using DV for video editing and VFX, and comparing that to some of the glorious DVD's that are out there.

2. Objectivity

You can't compare DV's 25 Mbit/s to MPEG2's 10 Mbit/s and conclude that "25 is bigger than 10, hence 25 Mbit/s is better", because the codecs are completely different, and you get a completely different bang for the buck in the two codecs. MPEG2 is interframe motion-based, and as such will open doors to compression possibilities not available with DV.

You can't base your conclusion on what some production house uses, either, since they'll obviously choose non-interframe compression for editing, like DV or MJPEG.

MPEG2 is only good for end-result consumer video, meant to be watched from start to finish, and you can't do a half-assed job encoding it, you have to do it right.

3. Conclusion

All I'm saying is, DV has lossy compression, on top of the 4:1 color thingy.

That's a fact. But if you think DV is better in quality than MPEG2, that's an opinion you're perfectly entitled to. ;)

If you think I'm praising MPEG2, you're wrong - I was one of those non-believers who wished DVD would die quickly, because the bandwidth was rediculously low, compared to what was already possible at the time. And I still think so, I've just accepted the fact that DVD is the best quality home video format at the time. :shrug:

...sorry, sequestrian.... I think we went... maybe a slight tad OT... -oops!

Cheers,
- Jonas

ggg
03-10-2003, 08:17 PM
Originally posted by jussing
Yes, transferring DV to VHS like that would definately to the job nicely.

-But if it's a Quadro4, maybe there's a good TV out? If there is, he won't have to go over DV tape, he can just play the DV file (or whatever format or codec he chooses) and record it directly to VHS.

(I just know some video cards' TV out look bad, leaving a black border around the picture, and making all sorts of refresh rate problems...)

In my experince the graphic cards TV out just can't keep up full screen in any codec with same quality as DV firewire out can. And DV firewire out doesn't require going to DV tape using a camcorder or or media converter to go to vhs or whatever.

derelict
03-11-2003, 08:31 AM
....and he didnt even come back to say thank you.... how rude!

KayosIII
03-11-2003, 11:31 AM
The general Idea is to convert your files as little as possible. If you are using MiniDV as your recorded input - Keep your projects DV until the last step... If you input comes from another format keep it that way.

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