TV/Video Capture Card

[Bowser]

I just purchased a TV/Video Capture Card and am curious about the technology and file types. I've noticed that the motion is more fluid at 15 fps than 30 fps, and I'm wondering if anyone can tell me the reason for this. I would think that 30 fps would be the best setting, but it is proving to be staggered and out of sync with the audio. I presume that the cause for this is the amount of data being pumped through the system--it's probably more of a hardware deficiency.

Does anyone have a firm handle on these video capturing cards and the various formats which I can use for improved viewing?

 

[Cris]

15fps is not considered acceptable.

The most common issue will be the speed of the hard disks. 5400 rpm disks are unlikely to make the grade unless they are of the high packing density type, e.g. 80GB+ disks with a 9ms response time.

The efects are worse if the video is analog. DV data via a firewire capture card will typically transfer less data but at a much higher quality than analog.

If you have slow disks then your best solution is to either buy faster disks, 7200rpm at least or buy an ide raid card and an additional slow disk. The ide raid cards allow the data to be interleaved across multiple disks and give an effective transfer rate of twice or better the rate of a single slow disk.

Going to SCSI might help but you will still need faster disks, and SCSI is much more expensive and really not needed with the latest faster IDE disks.

An even better solution is to obtain a firewire disk that gives some 400Mbits+ per second, that is 50MB/sec. To achieve 30fps with no dropped frames you need to maintain a steady transfer rate (not burst) of at least 5MB/sec. A firewire disk is more than perfect, and their prices are now quite acceptable. And they are external devices.

Lots of other isues here like turning off read ahead and read behind buffering on the disks. Accepting a faster fps but allowing more dropped frames, etc.

Hope this might help a little.
Cris

PS. Don't try capturing to your C drive if that is also a slow disk (5400rpm or less). Windows normally sets up a C drive with a small block size, and that is bad news for video capture.

 

[Boris]

Bowser,

Cris clearly knows more than I do concerning this issue, but there's something he forgot to mention. Depending on color depth and resolution of your captured video stream, as well as the video format (and therefore degree of compression) the actual bandwidth needed for playback varies. Your disk or memory subsystem may not be the bottleneck; rather it might be your CPU or video card.

For example, if you are playing a highly compressed video, the CPU has to do a lot of work to decompress each frame before displaying it. A good video card may offload some of that work (depending on compression algorithm.) For example, there are MPEG-1 and MPEG-2 hardware accelerators.

In general, the more frames per second -- the better. However, at around 30 fps any further increase becomes unnoticeable even to experts. That's why TV, for example, does 30 fps. So if with increased frame rate you get decreased performance, blame the hardware and not the frame rate.

I've got a simple (though very crude) test to see whether it's your CPU or your disk that's a limiting factor. Create a very large video file (multi-GB if you can) with a known number of video frames in it. Then open up the time window to see the seconds as they pass, and copy the large file to another location on the same disk, timing the operation to the nearest second. Take that time and divide it by 2. Then divide the result by the number of frames in the video file. This should give you a rather rough fraction of a second your computer needs to simply read one frame of video from its hard disk. If you want a more reliable figure, repeat the test several times and average the results across the trials. You can further compute standard deviation, or even the error margin, if you want. Naturally, to playback at 30 fps, the computer must be able to read 1 frame in 1/30th of a second. If there's extensive processing involved with each frame, then it would be nice if your computer can read 1 frame in as little as 1/60th of a second or less. Anyway, if the time you get is very small, then your disk is not to blame; rather you need a CPU upgrade (or a memory upgrade, or both -- depending on your CPU brand and model).

My 2 kopecks

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I am; therefore I think.

[This message has been edited by Boris (edited January 16, 2001).]

 

[Bowser]

Cris and Boris,

Thank you, gentlemen. My hard drive spins at 5400rpm and it has a 2 meg buffer, and the CPU is an AMD Athalon (I will try your test, Boris). I am using a Diamond stealth III video card with 16 megs, and I have 128 megs of system RAM.

"Windows normally sets up a C drive with a small block size, and that is bad news for video capture"

That might be it right there. The motion does pulse when I run at 30fps and high resolution.

"If you have slow disks then your best solution is to either buy faster disks, 7200rpm..."

When I built the system I was short on cash, so I went with the least expensive hard drive. I should have used my Visa, eh. A faster drive was always one of those things which would be nice, but wasn't needed, until now.

My one serious concern is that I want to burn family movies to CD and then send them to the grandparents, but I fear that they will not play well. How can I provide a movie on CD wich will work well on a many systems? Does anyone know which format/compression will work best for this effort?

"For example, if you are playing a highly compressed video, the CPU has to do a lot of work to decompress each frame before displaying it. A good video card may offload some of that work (depending on compression algorithm.) For example, there are MPEG-1 and MPEG-2 hardware accelerators."

Hmm, I need to investigate that issue more.

"...blame the hardware and not the frame rate."

I am certain that the hardware is the culprit. Your test sounds like a good way to determine where that bottleneck is located. My guess is that it is with the hard drive.

I thank both of you for you help.<img src = "http://www.exosci.com/ubb/icons/icon7.gif">

BTW:
After stressing over the high prices for video editing software, I found and purchased a nifty, useful editing software package while combing the software shelves in the store yesterday. I paid $2.99 (sale price) for the CD. I wasn't expecting much in the way of functionality, but it is proving to be more than I expected. <img src = "http://www.exosci.com/ubb/icons/icon6.gif">

 

[Boris]

Bowser,

Glad to be of any help. In general, if you want to tailor your videos to a low common denominator in hardware, you do the following:

1) cut down resolution. Usually, playback at at around 200x200 pixels still preserves all the fine details nicely. Even 100x100 works well in most cases (these are ballpark estimates; your playback window probably should not be a square, to preserve the aspect ratio of your camera.) Sometimes this is called "downsampling".

2) lower color depth. Rather than 32-bit or 24-bit color, try 16-bit color. Some formats offer "palletized" color; it almost always results in more compact encoding with little or no loss in quality.

3) the level of compression... There is a tradeoff here; less compression means less work for a CPU, but larger file size. If you want to put your movies on a CD, you may feel the limitations of the 700 MB maximum. When you write a movie from some video editing suite, you usually have a choice of several formats. Some formats may offer options to adjust the level of compression. As a general rule of thumb, just about any format can deliver from near-perfect reproduction with little to no compression, to highly compressed output with loss of detail and artifacts. My best advice is to simply test these out. Take a movie and save it in each of the available formats. Compare the resulting file sizes and playback quality. Choose a promising subset of formats and play with their settings... It may take a couple of hours, but at the end you will know the rough characteristics of each format (you may want to write them down somewhere for future reference.) One thing to keep in mind when choosing a format, is whether this format will be supported by the software of whoever you want to see the videos. Formats such as AVI, Quicktime and MPEG-1 are supported by almost any modern player.

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I am; therefore I think.

 

[Cris]

Bowser,

Your video display card sounds fine, I think your version is an AGP 2 at least.

I have found that you should have enough CPU power with a chip rated at 300MHz or more. Slower than that and you might run into excessive cpu utilization with the software codecs you will be using. Professionals use hardware codecs to avoid such issues, but such capture cards start at around $1500 and go up fast.

Some other unpleasant characteristics come from IRQ sharing. Try to ensure that the Video capture card, Video display card, and the sound card are all using different IRQs. If you can’t change your CMOS settings to achieve this you can probably move one or more of the cards to different slots.

I work entirely in DV format for all my home movies, and because I like to show the movies full screen and at high quality I am not prepared to accept any significant compression. With this format I expect around 1GB of storage for 5 minutes of movie time. That means that a CD will hold around 3-4 minutes, and unless you have a high speed (72X+) CD-rom drive you would be unlikely to be able to play back fast enough.

For the moment I dump out my completed, edited, movies to another DV tape (becomes my master) – holds about 60 minutes. I then also produce VHS cassettes for distribution to anyone who doesn’t have DV playback devices.

My daughter often records entire local plays and shows, typically 2 hours per show, using multiple cameras. She then downloads all the raw footage to hard disk, usually about 70GB. She then edits that footage, merging scenes and close-ups from the different cameras, to produce a final cut. This requires quite a few more GBs for working storage. But this is quite serious stuff because she then produces some 30 copies on VHS tapes and sells them.

It took me quite a while to put my system together so that it would run smoothly with maximum quality. This is probably more than you plan, but it is great fun.

I do know that Compaq is about to release, or has already, a writable DVD drive designed specifically for the home movie enthusiast, and sorry I don’t know the prices yet. That is going to be perfect, I always hated the drop in quality of the VHS output compared to the digital masters I produce.

From your description I am quite sure your hard drive is too slow. I reckon the minimum you need is a new second hard drive such as the 30GB Maxtor 7200rpm that sells at around $150, I think. But the new firewire disks would be far better, at around $300 for 30GB.

I think you now have a view of the higher end solutions and Boris has described the lower end. I guess you’ll land somewhere in-between.

Have fun
Cris.

 

[Bowser]

Cris and Boris,

No doubt, I bought into the low-end of video editing. I think that I will be shooting more for quantity rather than for quality. The kid at Fry's was pushing one of the better cards ($350.00+), but I told him that the price didn't reflect my needs, even though it would be nice to have the best tools.

I did notice that Fry's was selling the recordable DVD's, but I haven't seen the Read/write drives yet. I suspect that they will start appearing on the retail shelves very soon. Nonetheless, I'm still trying to get some good use out of my CD burner. I was hoping that some family photo's and video clips would put it to good use.

Well, I will tinker with the system and see if I can get better performance. I thank you again for your help and expertise.