Quantcast Can't capture AVI at 720x480 with ATI 9600XT? - digitalFAQ Forum
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01-09-2005, 05:38 AM
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Hi,

I posted this on another forum at a different website but now that I think about it I probably should have posted it here first, so please excuse my redundancy if anyone has already read this elsewhere...

I'm using an AIW 9600XT, trying to cap from S-VHS using the Huffyuv codec in ATI MMC.

When I first installed the 9600xt a month or two ago I was able to cap AVI at 720x480. Since then I've upgraded the ATI software several times (doing a thorough uninstall each time as per recommendations I"ve read on several websites) and I just recently (yesterday, actually) downloaded and installed the latest drivers,etc. from the ATI site. There seems to have been a slight improvement in picture quality from TV and VCR sources, but that could be my imagination.
Here's the problem. When creating a preset for recording AVI from the S-Video input, the highest resolution available is listed in the drop-down menu as 704x480. I'm almost 100% positive I've capped AVI using Huff at 720x480 previously and I can't figure out why it's not listed as one of the options for AVI now (it IS listed as an option for MPEG2 capture, though).

It's my understanding that the native resolution for the card is 704x480, but I'd still like the option to cap at 720x480.

Has anyone else ever experienced this?

What could have caused that option to disappear? That's what I really would like to know...and of course how I could get it back, short of rolling everything back to an older MMC, which I'd really rather not do.

Thanks in advance...
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  #2  
01-09-2005, 11:37 AM
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I'll look into some hacks, we may be able to forced 720 back in (will need some time to do this, and it may not work anyway), but your initial findings are correct:

- driver upgrade improving quality probably is imagination
- rolling back to another MMC version (like the most-stable 8.7) will achieve 720
- The native size of the chips is very close to 704x480, and therefore best to capture at. Absolutely NO RESIZING internally would be needed to interpolate a 720x480 capture.
- the option disappeared because removing that resolution was an update to the ATI MMC 9.x series, and rightly so

All good and non-limited NLEs, encoders, and authoring applications will recognize 704x480 as a valid 4:3 resolution for work intended to go to DVD.

Is there any reason you really want 720x480 instead of 704x480? Maybe we could look into that too. The quality perceptions between the two are negligible, especially if you're using something like VHS or tv signals as the source (which are FAR FAR below this res).

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01-10-2005, 03:32 AM
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Hi,

That's interesting. So the 720x480 res for AVI was intentionally removed by ATI? This was a move towards insuring the best capture quality, if I understand correctly?

To extrapolate, they then left the 720x480 option for mpeg2 capture to insure compatibility with programs that might not accept the other resolutions? Or am I reading to much into it?

The only reason I was wondering how I could continue to capture at 720x480 was because in certain editors (I use a slightly older version of Adobe Premiere and a brand-spanking new After Effects 6.5) the pixel aspect ratio for imported 720x480 footage is automatically interpreted as 0.9 (in other words, the same as DV footage). Imported 704x480 footage, however, sometimes shows up as 0.9, whereas other times the software defaults to a square-pixel interpretation (I'm only talking captured video here, not animation or other stuff generated on my PC, which is almost always square-pixel footage). I'm sure most of it is dependent on the codec used when capturing, but as I only use a few codecs I haven't really done a lot of research in that area, and truth be told most of my source is DV, except for what I capture through the the 9600xt (which is VHS tape and the occasional TV broadcast).

Speaking of which - I wasn't really clear when I mentioned the picture quality, or seeming improvement thereof. The only improvement I saw was when using the TV tuner. Running cable TV into the card, the channels seem to be clearer than they were before I upgraded to the latest software. Not perfect, mind you, but definitely cleaner. Could it be that the card is doing a better job of "locking on" to the different channels when scanning through the frequencies? I haven't changed any other hardware or software.

Back to the question I had started with; I've seen mention of possible artifacts when capturing at 720x480 which are not present when capping at other resolutions. Is this a result of the re-sizing you mentioned? Some folks have referred to interlacing artifacts, and I'm not 100% sure what they look like.

And since I mentioned codecs and interlacing, here is a related question; you mention on your site that Huffyuv is designed to capture TFF- which is apparently also what the 9600xt is designed to do. If I import TFF Huffyuv footage into a project in my NLE, I wonder if rendering out the final video as BFF (which I sometimes do when mixing analog 9600xt caps and firewire capped DV, for example) creates any quality loss?

Once again, thanks for all help....
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01-10-2005, 09:54 PM
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Resizing causes aliasing issues. Interlace is something entirely different, but it has always been my belief that interlace may cause aliasing to be worse. (Though keep note that retaining interlace, even with aliasing artifacts, will still be FAR BETTER quality than de-interlace artifacts.)

All capture chipsets (found in both capture cards, DVD recorders and other digital acquisition devices) grab video with a certain pre-determined resolution, based on the chipset. It can then resize to the specs as instructed by firmware or the user. Now the question is always: how well does it resize? And that is the problem... most hardware resizes poorly, with few exceptions.

A general rule of thumb in the image world is to try and only resize in quarters: 25%, 50%, 75%, 125%, 150%, etc. Aliasing is LEAST NOTICEABLE on these settings.

The ATI card plays nice with this philosophy. A 352x480 capture tends to look every bit as good as a 704x480 (at least in situations where the source is around or under 352x480 D/A equivalent... like VHS, cable, etc).

This is another reason "cropping" video is a bad idea. It causes both a resize and can introduce aliasing problems.

DV tends to be pretty sensitive to aliasing for some reason, at least the 4:1:1 NTSC consumer version. That aliasing is caused mostly by compression, and I've seen it infect even semi-professional Matrox cards.

Here's a sample of aliasing artifacts:

720x480 skewed image (blown up 300%):


704x480 native image (blown up 300%)


NOTE: Now, let there be no misunderstanding. These images are simulated in Photoshop (running actual tests would take quite a while). However, these are VERY CLOSE to what I have seen numerous times in the past 4 or so years of digital editing/conversion. And while you may be thinking "these are 300 percent, of course they're more obivious!" .... trust me, you can see them at 100% size too ... the upsize was so you could see them better.

To see what an INTERLACE artifact looks like, read this guide: http://www.digitalfaq.com/capture/interlace.htm

Adobe Premiere does not always play nice with HuffYUV compression. I use Adobe Premiere 6.5 most of the time here, and most often feed it 640x480 uncompressed YUY2 AVI captures or captures using the Morgan MJPEG compression codec (motion JPEG = MJPEG, not MPEG). Not free, but $30 is not much. MainConcept also has a MJPEG codec these days.

And you may now be thinking: Wouldn't 640x480 cause an alias skew? And then would re-encoding skew again? The answer is "not really". Skew is most often a problem in hardware. Software has any number of advanced algorithms available to resize, unlike hardware which needs fast-n-dirty methods, not advanced methods that would require large CPU/RAM. And a hardware DOWNSIZE is often fine (at least on a good card like an ATI), it's the UPSIZE that more often causes problems both in hardware or software. It's easier to throw away data than it is to create new data. Yet another reason to not try and capture too high above your source resolution.

The 640x480 is 1:1 and easy for Premiere to deal with. The software encoder should be able to re-encode the file with NO PROBLEM in high quality. Very nifty way to work with video, especially medium res sources like VHS, S-VHS, etc.

________

I've heard several times where people have reviewed an ATI MMC update as having improved the tuner quality, but it's always been very randomized, nobody ever agrees on it. My tests have NEVER shown any real difference between the 8.x and 9.x versions, regarding improved tuner quality. Not sure what to say here. If your cable is anything like mine, it's probably nothing but coincidence. Aerial signals can be affects by almost anything (moon phase, weather, cloud cover, sun activity, etc).

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