About to start capturing... trying to confirm some ideas

[PaulJBis]

Hi all:

I'm about to buy my first capture card, and after reading this forum for a while, I'd like to post here some of my conclusions, to see if I'm in the right track or there is something I misunderstood:

1) I want to use the card mostly to capture stuff from TV/VHS and edit it later, which means that I won't be needing a card with hardware MPEG2 encoding. Instead, I should buy anything with a BT878 (like a Hauppauge WinTV) and capture using the Pegasus MJPEG codec (I do have the registered version). My computer is a Pentium 4 2.6 Ghz with 1 Gb. of RAM, and my media disk is a 250GB SATA 7200 rpm. Maxtor. Would this be enough to capture full resolution PAL (720x576) using MJPEG, with a quality setting of say 18-19?

2) From what I've seen, audio sync problems are caused in 99% of cases by dropped frames, which are caused by the computer not being able to keep up (which means that hardware-based MPEG2 cards don't have those problems; am I right?). Is there any secret to avoid sync problems, other than "don't drop frames"? (and therefore, have a fast enough computer to avoid dropping frames). Any particular kind of capture card to avid/pursue? Is the above mentioned computer fast enough to capture without problems in this regard?


Thanks in advance.

[drcl]

yes your specs should be well able to capture with those settings.

dropped frames are caused by audio synch problems usually, not the other way around. the audio synch problem is caused by the video capture and the audio capture running off differnt timing circuits/oscillators

the only adequate solution to this i have found on bt878(a) captures is to use virtual dub sync, which resamples the audio to fit the video length on the fly.

the one caveat of this... if there is a major bottleneck on the pci or the cpu bus the audio can will be dropped and you will have a major audio sync problem. best to have no other programs running.

[PaulJBis]

I see. Thanks for your reply.

So what can I do to make sure that the capture card and the sound card are in sync? My sound "card" is an on-board Realtek AC97 chip (and my mainboard is a Gigabyte 8IPE1000-L); are those known for being problematic? Should I look for a capture card with a chipset other than the 878? I know about not using any other program when capturing, but other than that, what can I do to make sure? I hadn't heard of VirtualDubSync before reading this board, and I'd rather not install *yet* another version of Vdub... :) (I already have the normal version and Nandub).

[ppera2]

With your hardware and Mjpeg you will not have async problems due to overload.


But problems may happen by VHS tapes in bad condition. Solution is usage of mentioned VCR version of V Dub, or probably better try latest versions of genuine Virtual Dub (1.65 at moment). BT 8x8 tweaker can help to make sync better too. Usable only in Virtual Dub and mods.

[PaulJBis]

I see. And what about capturing from live TV? I'm not really that interested in capturing from VHS, actually.

And, please correct me if I'm wrong, but if audio sync issues are caused by the capture card and the sound card having oscillators running at different frecuencies/speed/whatever, that could be a problem regardless of how powerful my computer is, right?

[drcl]

yes, its nothing to do with the power of your system.

Most people on here use virtual dub or virtual vcr, both of which deal with this problem, either by dropping/adding duplicate frames to maintain a/v sync or by audio resampling. The number of frames dropped per hour will be individual to your system. if you are lucky it might be none.

dropping/adding frames isnt so noticeable on progressive material but on interlaced a very noticeable field flutter will occur if a frame is repeated.

its impossible to know if your ystem will cause repeat frames or actual drop frames to maintain sync until you actually try it out.

my own setup uses realtek onboard also and i use a pinnacle pctv rave. it adds about 20 frames per hour when i use standard virtual dub. so that is 1 field flutter every 3 minutes, therefore i use virtual dub sync.

everything you need to know is here:

http://www.doom9.org/capture/start.html

or

http://www.geocities.com/wilbertdijkhof/ACG41.zip