capturing hi8 video

Christ Reynolds · 05-09-2003, 02:38 PM

ive looked at the threads here about this, and they always stray towards which hardware to use. i already have a crappy capture card, and upgrading isnt an option. using my ati tv-wonder pci, i am trying to capture hi8 video from my camcorder. i use virtual dub, and everything works, but i read somewhere about getting all 400 scan lines, and if you do a normal capture, you only obtain 200. and i'm not sure about which bitrate to use, i dont want to use a ton more space than i need, and i dont want to use too little. anyone know which settings i should use for audio and video? my camera is a sony ccd-tr516, capturing with virtualdub and a divx 5.01 codec, thanks

CJ

Ken Chan · 05-09-2003, 08:08 PM

Scan lines are horizontal, so they actually determine the vertical resolution. All (NTSC) TVs have about 480 visible scan lines, and this number is fixed; it's the actual path taken by the electron beam when it "paints" the picture. The variation in different video formats is the amount of resolution within each scan line (i.e. the horizontal resolution), the color sampling and accuracy, and stuff like that.

Horizontal resolution is traditionally -- and confusingly -- expressed in "lines": how many alternating black and white vertical lines can be expressed in a width that is equal to screen height. This is so that vertical and horizontal resolution can be compared to each other, and sometimes called "television lines" or TVL. Hi8 and SVHS are 400 TVL; regular VHS is 240; broadcast (NTSC) television is 330.

Computer resolutions, including those for capture, express the actual number of pixels across the screen. So to convert a TVL value for a 4:3 aspect ratio into pixels, you must multiply by 4/3. 400 TVL yields 533. With 480 scan lines, that means that to capture a theoretically ideal Hi8 frame, you would need a minimum resolution of 533x480. Of course, things are rarely ideal so more horizontal resolution is a good idea. 640x480 has the advantage of being 4:3, so video is not squished in either axis when viewed on a computer. 720x480 is the common DV and DVD resolution, and many programs prefer it.

There really is no such thing as a "normal capture". Particular hardware will capture up to a certain resolution, and the capture program has to support it. I used an old non-PCI, non-Wonder ATI TV, and the ATI program only went up to 352x240. (It only captures every other scan line, or one field.) But when I used VirtualDub, it would do all the scan lines, 352x480. I vaguely recall some menu item to use "nonstandard" resolutions -- you might need to choose that. It's possible that the TV-Wonder doesn't do 720x480, but it might do 640x480.

Once you choose the resolution, the bitrate is a matter of being "enough". If it isn't, you should be able to see it. I'm not familiar with DivX, so I don't have any ballpark recommendations. If you choose too much compression (low bitrate), besides hurting the picture quality, it might be too much work for the CPU, and you'll drop frames because it can't encode them fast enough. If you choose too little compression, your drive might not be able to write all that data fast enough, and you'll drop frames that way. Obviously, fast CPUs and drives will solve those problems.

//Ken

Scott L · 05-09-2003, 09:46 PM

640x480 should be a safe resolution to capture at. Divx Pro 5.05 has a handy profile tab in its configuration menu which will automatically set the important settings for you.

For bit rate at tht res I'm thinking around 2000kbps, but raise or lower it to your liking. When capturing NTSC TV programs I do 320x240, Divx Pro 5, 1000kbps, 1-pass. Plus although multipass encoding takes up less space than 1-pass sometimes the video will get out of sync with the audio when advancing through the timeline. If you approach 4000kbps just for video look into using the HuffYUV codec which is lossless.

For audio just select 44/16 uncompressed.. later you can use RazorLame to encode it as a 192kbps MP3 if you need to conserve space. Oh and CBR over VBR to save yourself from syncing problems later.

Christ Reynolds · 05-10-2003, 01:02 PM

thanks for the great info, guys. i find that huffyuv works better than divx for me. when i import into premiere, huffyuv doesnt bog down the editing, but with divx, you could barely even use it. however, once i go above 352x288, i get these strange horizontal lines across the screen. they arent enough to prevent me from seeing the picture, but they are definitely not something i want in my finished product. think this sounds like it could be the capture card? i'm going to try to update my capture drivers, although i doubt that is the problem. prob just my low quality card. happens with all the codecs ive tried so far, so i'm guessing it is the card. ok off to try it once more, thanks again

CJ

Jeff Kleist · 05-10-2003, 01:16 PM

DivX is not designed as an editing codec, and Premiere only deals with whole-frame formats. I suggest you find and use an MJPEG codec

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Scott L · 05-10-2003, 02:05 PM

Oh you want to throw it into Premiere and edit? Scratch DivX then for capturing, Premiere works optimally when you import unompressed material (or semi-compressed in YUV's case). For archiving your finished product using less HD space then look at using DivX.

As for the capture card it pretty much sounds like it's the culprit. The FlyVideo 2000 let's us capture at up to 720x576 and has been getting good user reviews on AVS. I actually ordered one a couple days ago from Technobazaar and it's on its way here ($40 shipped). This will be capture card #3 after being dissatisfied with an XCapture and Asus TV Tuner card.

Ken Chan · 05-11-2003, 04:19 AM

Quote:

once i go above 352x288, i get these strange horizontal lines across the screen

Do you mean comb artifacts due to interlacing? The only decent sample I could find is near the bottom of this page, in the section titled "Combing", just above the section titled "Vertical Filtering". If that's what you see when things move on-screen, that's normal; when you play it back on a TV, it looks correct. If you intend to watch the video primarily on a computer, then you can try deinterlacing it.

//Ken

Jeff Kleist · 05-11-2003, 10:59 AM

Don't capture at 720x576 unless you live in PAL land. Just FYI

Christ Reynolds · 05-11-2003, 09:18 PM

Quote:

Do you mean comb artifacts due to interlacing?

well i checked out the link, and its definitely not like that. the lines seem to be at random, they are of different lengths, and they dont usually stretch across the whole screen. it must be the capture card, because everything else is fine at 320x240. i'll look up the card scott ordered, $40 shipped is attractive.

CJ

Christ Reynolds · 05-11-2003, 11:33 PM

also i forgot to mention, i am getting a decent amount of video noise during capture, would this go away if i upgrade to a better card, or could it be from my camera? i'm using a composite connection with throwaway cables. a better cable doesnt do much better of taking it away.

CJ