Full frame cap problem - HELP PLEASE!

[Triffid]

This may be a long one, but please bear with me. I need some help!

I have done a lot of video capturing, but it was mosty single field for VCD production. I've now moved up to DVD, so I am trying to get full frame capture working properly. For this most part this is no problem (my system is generally up to it, and I get no drops and vidoe that, on the surface looks great)

My problem is that I get field reversals when recording from VCR/camcorder. That is, after some time I must loose a field or something, and the orider reverses. I can see this happen if I split the fields in Virtualdub to veiw them, and TMPGEnc confirms it if I only run the effected parts through the 'filed order detector' independantly. Needless to say the resulting MPEG gets a bit choppy during the reversed part. At a later place it returns to normal again.

I have also tried capturing directly from TV. In this case, NO PROBLEMS occur.

My camcorder has a built in TBC. If I turn it on, the foeld reversal problem goes away BUT is replaced (at the approriate point) bay a messed up frame. Normally a field is shifted sideways, or there are major colour problems. It is possible that the TBC in the camera is not up to the task (but how would I know?)

Recapturing the the effected segmat of video (stating just before the problem area) always works OK, so it is not dependant on the actual recorded signal. However, it is not possible to predict or easily find where this happens so it is not an option for resolving the problem.

So what I wuld like is to hear any opinions on how to deal with this. Especially from anyone who has actually experienced the problem before.

Also, does anyone with TBC experience think that using an external TBC will fix my problem.

One more comment, this problem is independant of - OS, video signal type (S or C), capture drivers, compression codec, and occurs with both my VRC and my camcorder (but not direct TV).

The common bits of my system are:

ASUS V7700 deluxe capture card. Virtual dub (although I have also used Virtualdub - sync, but I believe the only diffence is in the handling of audio). The system is PIII 1GHz, 7200RPM UDMA5 drives, Win98/Win2k...

TIA.

[Triffid]

I'll give this one more try (please read the above post!!!!!)

So, has anyone here ever used a Time Base Corrector, and what did it do for you?

Also, anyone in Australia know a good Time Base Corrector for home capture use (and where to get it)?

More also, because I'm desperate, and not because I am giving up on my capture card. Has anyone with an ASUS video-in card (esp V7700 deluxe) captured significantly long video (eg greater than 1 hour) at full frame settings (ie both fields) and got it to work OK for them??

I really like doing this stuff, and this problem is really pissing me off!


HELP!!!!!!!

[RoopeT]

I have also tried capturing directly from TV. In this case, NO PROBLEMS occur.

So you already know there's nothing wrong with your capturing method, capture card drivers etc. BTW, I also use VirtualDub synch for capturing.

Some old VHS tapes are really impossible to capture with any kind of equipment (correct me if I'm wrong). I once tried to capture an n:th generation VHS copy and got 12000 dropped frames in an hour! No TBC can fix that.

My camcorder has a built in TBC. If I turn it on, the foeld reversal problem goes away BUT is replaced (at the approriate point) bay a messed up frame.

I believe my newly bought JVC SVHS with built in TBC does this too, and it's really thought to be the best VCR money can buy. Even a TBC can't fix everything.

My problem is that I get field reversals when recording from VCR/camcorder. That is, after some time I must loose a field or something, and the orider reverses.

I would try to deinterlace the capture and encode as progressive. Have you tried that and if yes, how did it come out?

[Triffid]

Thanks for the reply.

Yes, I'm pretty confident of the capture method. The only point that I can imagine a problem occuring is in the hardware interface. For one reason or another, it is not up to the job (ie I need to either fix what's coming in, or replace the card with something that will work). I put my hope in a Time Base Corrector because, a) it sounds feasible that this is some sort of timing issue and b) it's got to be useful for something anyway (even if I do need a new card...eventually).

I haven't tried deinterlacing, in this instance. From my previous experience with deinterlacing, I am not greatly impressed. The main reason I have moved from (S)VCD to DVD to be able to handle interlaced video with sufficient bitrate to get good quality. Deinterlacing would put me back where I was...un-smooth motion...not where I want to be.

I intend to try to get hold of a TBC from somewhere and give it a go, but if that fails (as I guess you are suggesting it may) I will need to look at new capture hardware. But, what is to stop the next unit I get having the same sorts of problems? ...................................

Thanks again for the reply!

[Triffid]

I found a process which appears to fix my problem, so I though I would post it in case anyone experiences anithing similar.

After looking carefully at lots of failed attempts, I realised that when a frame was dropped (due to correction for either audio sync or capture rate correction) then after the drop, instead of:

frame x Upper - frame X lower - frame X+1 Upper - frame X+1 lower ...

I got something like

frame X+1 upper - frame X lower - frame X+2 Upper - Frame X+1 lower ...

So I made a guess that there was some resynchronisation problem due to the receiving frame order the capture (or whatever). SO, I set Virtualdub to swap fields on capture, and now, after dropped frames, everything resynchs OK. However, the MPEG2 encodes were a little bit (not much) jittery, so I need to swap the fields back again before sending the video to TMPGE (either with a filter or in the compression codec).

The one annoyance now is that the 'swap field' setting in Virtualdub capture mode does not seem to get saved along with all the other values, so I need to remember to set it each time I capture. (Anyone who knows how to fix that, please let me know)

I have no idea where the fault really is, but this seems to fix it. (except when there is really a fault on the tape). SO for now, I will not be spending A$550 on a Time Base Corrector!