Help with lines on capture (but not preview)

[arjones]

Hi all

I've just begun converting VHS and camcorder (DV) tapes to DVD. I've read many guides and downloaded a lot and in general it's going pretty well.

I have one problem though. When I view the input from the camera in the capture software, it's perfect, but as soon as I actually start to capture it, I get lines on the screen. Sometimes they're worse than others, but there's almost always something there, even if it's barely noticeable.



You can see it's pretty bad in this example (as is the focus...)

My setup is as follows:

Panasonic mini-DV video camera connected to AV inputs on VCR
VCR aerial cable connected to input of TV Capture card
VCR audio line out connected to line in of (onboard nVidia) sound card in PC

The PC is an Athlon 3200+, 1GB, 300GB Maxtor drive used for the capture
The capture card is a Medion 7134 (Philips SAA7134 chipset)

I'm currently using VirtualVCR to capture, and compressing with PICVideo M-JPEG, but this seems to happen irrespective of software and compression.

Just to repeat: when I watch the input video in the preview window, it's fine. It's only once I hit capture that the lines appear. I tried turning off the preview during capture in case it was related to that but the lines are still in the avi on disk.

If anybody has any ideas, I'd be very grateful

Andrew

[FulciLives]

A mini-DV cam has IEEE-1394 output (this is also called FIREWIRE). That is how you should connect the mini-DV cam to the computer. Then use a program such as WinDV to capture.

That will give you a perfect digital bit-for-bit copy of the mini-DV cam stuff.

If you want to capture from another source like a VHS video then you have to use your capture card UNLESS your mini-DV cam support analog input (but supposedly most European models do not support this).

As for the lines when you capture with your capture card ... that is rather bizarre. I'm not sure how to explain it because it looks like it is more than just "interlaced artifacts" as are to be expected but instead appears to be some sort of ... error for lack of a better word.

Like I said you should have the mni-DV cam hooked up via IEEE-1394 (or FIREWIRE as it is also known) but these "lines" that you do get ... are they only from the mini-DV cam or also from VHS captures? What about another source like cable or satellite TV?

Maybe you can edit a capture file so it is very short (file size of 99MB or less) and post the AVI file on the RAPID SHARE WEBSITE which is free. That way we can download it and see exactly what you see. Sometimes having a video sample instead of a still image helps when trying to figure out problems.

- John "FulciLives" Coleman

[arjones]

OK thanks I'm now capturing from my camera using Firewire after a cable-shopping trip.

No lines, predictably!

I still have to do the VHS tapes so I'll upload a short capture later (maybe not today) with an example of the lines.

I think it might actually be related to I/O activity on my motherboard. I figured out that I CAN make the lines appear during the preview, if I perform some activity on my PC. It doesn't seem to be strictly linked to disk access, but I think it's related... e.g. if I start a defrag then it will create the lines in the preview window to start with, and then they'll reduce to almost nothing even though the disk is still going crazy.

I bought a new filtered/shielded aerial cable today. Probably won't fix it (haven't tried yet) but surely can't make it worse

I'll post again with an update, but thanks for your help so far, and if what I wrote above gives any more clues in the meantime then please let me know!

Andrew

[Bjs]

Seperate the feeds from the vcr .

1: Audio to line-in on sound card (rca to stereo headphone socket cable)
2: Video to capture device input (via rca connector / convertor) ... never use rf cable (cause's interference) .

This should clear it up from the vcr .

[FulciLives]

All I can really say for now is that you should leave the computer alone and do nothing in the "background" (i.e., defragging) when you capture.

This applies to using the capture card as well as FIREWIRE capture (really a file transfer) when using the mini-DV cam.

Using the computer for ... whatever ... when also capturing/transferring is a bad thing that can cause all sorts of errors.

Also shut down or close the preview prior to capture (if your software supports that). This is probably more important to do with the capture card than the FIREWIRE transfer.

- John "FulciLives" Coleman

[edDV]

...

...
I think it might actually be related to I/O activity on my motherboard. I figured out that I CAN make the lines appear during the preview, if I perform some activity on my PC. It doesn't seem to be strictly linked to disk access, but I think it's related... e.g. if I start a defrag then it will create the lines in the preview window to start with, and then they'll reduce to almost nothing even though the disk is still going crazy.
...

You have discovered the problem. Those lines in the upper third are the result of lost sequential pixels (dropouts) in one field. These can be caused by tape problems (e.g. dirty heads or chipped tape) but MiniDV camcorders are designed to mask those by substituting information from the previous line to mask the error. What you are seeing is pixel data being discarded because the path to the hard drive is blocked by the CPU asserting priority on the drive. DV is a constant stream. If the drive isn't ready to accept the data, the data are discarded. This differs from a network file copy, where there would be a request to resend the missing data packets.

[FulciLives]

...

...
I think it might actually be related to I/O activity on my motherboard. I figured out that I CAN make the lines appear during the preview, if I perform some activity on my PC. It doesn't seem to be strictly linked to disk access, but I think it's related... e.g. if I start a defrag then it will create the lines in the preview window to start with, and then they'll reduce to almost nothing even though the disk is still going crazy.
...

You have discovered the problem. Those lines in the upper third are the result of lost sequential pixels (dropouts) in one field. These can be caused by tape problems but MiniDV camcorders are designed to mask those by substituting information from the previous line to mask the error. What you are seeing is pixel data being discarded because the path to the hard drive is blocked by the CPU asserting priority on the drive. DV is a constant stream. If the drive isn't ready to accept the data, the data is discarded. This differs from a network file copy, where there would be a request to resend the missing data packets.

My understanding edDV is that he was having this problem when using a PCI TV tuner type capture card. He switched to FIREWIRE for the mini-DV cam and says it is now capturing/transferring A-OK but ... he still has some VHS videos to capture and the capture card is still "acting up" in this way from the VHS VCR input.

At least that is how I read it to be.

- John "FulciLives" Coleman

[edDV]

...

...
I think it might actually be related to I/O activity on my motherboard. I figured out that I CAN make the lines appear during the preview, if I perform some activity on my PC. It doesn't seem to be strictly linked to disk access, but I think it's related... e.g. if I start a defrag then it will create the lines in the preview window to start with, and then they'll reduce to almost nothing even though the disk is still going crazy.
...

You have discovered the problem. Those lines in the upper third are the result of lost sequential pixels (dropouts) in one field. These can be caused by tape problems but MiniDV camcorders are designed to mask those by substituting information from the previous line to mask the error. What you are seeing is pixel data being discarded because the path to the hard drive is blocked by the CPU asserting priority on the drive. DV is a constant stream. If the drive isn't ready to accept the data, the data is discarded. This differs from a network file copy, where there would be a request to resend the missing data packets.

My understanding edDV is that he was having this problem when using a PCI TV tuner type capture card. He switched to FIREWIRE for the mini-DV cam and says it is now capturing/transferring A-OK but ... he still has some VHS videos to capture and the capture card is still "acting up" in this way from the VHS VCR input.

At least that is how I read it to be.

- John "FulciLives" Coleman

I see. It is the same issue of sharing a single drive for capture and OS activity. Capture off a non-encoding tuner card results in higher data rates to the hard drive than DV so the problem is worse.

Also some DV capture software like WinDV have buffers set in memory to store small amounts of data overflow to the drive but at datarates near 4MB/sec this buffer will fill quickly.