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50fps capture on PC!
13.09.08 at 21:59:23
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Well, I didn't have any better ideas on how to name this thread, so let me describe the situation:

Lately I've been having some discussions with Christos about capturing video from the Ataris for his YouTube channel ( if you don't know it yet Smiley). Mainly the problem was that he was getting interlacing artifacts or low frame rate capturing (25-30 fps). Acquiring a newer capturing card didn't solve his problems.

At the same time I was tinkering with the idea of getting a capture card or a new monitor for my MegaSTE, with the later preferable as I don't have enough desk space to accomodate yet another monitor!

Then I had some discussions with my brother about this and he borrowed a capture card so we could play around. As I don't have a composite cable atm my experiments were conducted with a good old RF cable. After a quick run of some programs we were disappointed to say the least:

  • The built in software refused to capture at a rate faster than 25 (or 30 for ntsc) fps, resulting in choppy performance.
  • DScaler had problems reckognising the card, so I didn't really have much to do - it just didn't work.
  • Virtualdub could be forced to 50fps, but what it actually did was to capture one frame in two (in 50fps) and interleave their scanlines, so it gave us a 320x400 window (this we assumed was because the image is progressive and not interlaced, and because of that, the capture hardware was baffled. Or maybe because of the 313/313 mode the ST uses instead of 313/312).
  • We tried a commercial software too, ChrisTV, and we almost had what we wanted (i.e. 50fps). But then we got strong interlacing artefacts, which we kinda solved by turning on the ffdshow deinterlacing filter. But that led us to performance problems because we had to turn on some other filters too in order for it to still have 50fps capture rate.

In the end my brother had to take the card back to its rightful owner.

By sheer luck though he discussed this with another friend who gave him an old capture card he wasn't using for free. Bringing this card home, I found out that it was one of the old Hauppage PCI cards that have the bt878/9 chip, which is famous for being very flexible with its programminng.

Immediately I fired up DScaler, tuned the MegaSTE channel and was blown away - 50fps out of the box, no tinkering required! Hooray!

One final hurdle had to be overcome though, and that was the PC monitor vertical refresh. This I had done in the past and is easily solvable, as long as you have a CRT monitor (Wink). Download powerstrip, set a custom resolution with 50hz refresh rate, and presto! Flickering screen, but 50hz action. I swtiched fullscreen on in DScaler and never looked back since!

Well, there are some things that can be improved, notably:

  • I still use an RF cable. Using composite directly from the monitor output should give magnitues better picture quality (I guess I can use Aly's scart cable with a scart->svhs converter)
  • Because of the above, pictue quality atm leaves a bit to be desired. Of course a temopal solution is to switch on some filters which reduce noise to very low levels (almost not noticable).
  • As of writing I still haven't tried capturing to disk, so I can see if 50fps sustained capture is possible on my system (and I guess that should be interesting to people that make videos Wink). Well, not enough hours in the day I guess.... Smiley
« Last Edit: 13.09.08 at 22:02:57 by ggn »  
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Re: 50fps capture on PC!
Reply #1 - 11.02.09 at 13:35:59
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I suspect you used the progressive scan option in Dscaler. Though my pctv rave has the bt878, it seems that progressive scan isn't supported. Any ideas?
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