Problem capturing damaged miniDV tapes

[alex-kas]

Hi, Folks,

I got a weired problem capturing some miniDV tapes. Well, I knew in advance tapes are damaged. The playback on the camera is distorted and the video is jumping, i.e. the movie is not smooth.
So, I tried to capture with two tools. dvgrab in linux and premiere pro in windows. I have analyzed a particular set of frames and paid attention to the original timecode (analyzed with the help of dvdate utility). What I got:
In premiere for some given second I have all 25 frames (I have PAL) but the original frame numbering goes like 0,1, 2, 3, 4, 5, 6, 7, 8, 8, 8, 11, 12, 13, 14, 15, 16, 22, 22, 19, 22, 22, 22, 23, 24. As the consequence I have a distorted playback BUT the average speed is OK. So, looks like a bad quality movie. Also the picture does not disappear on those repeated (broken) frames. Kind of premiere extrapolates it somehow.
After dvgrab, however, I only have the following sequence of frames: 0,1, 2, 3, 4, 5, 6, 7, 8, 11, 12, 13, 14, 15, 16, 22, 23, 24 and this clearly results in an overspeeding and hopping movie. Looks like a movie from the beginning of 20-s century.

Hence, both are not good but apparently premiere is a bit better. Nevertheless, dvgrab works way much better in splitting scenes. This is because it splits scenes how I would expect it to be while premiere splits EVERY place the timecode is broken, for me it is two times a second in average.

The question therefore is: is there a way to explain dvgrab NOT just to trash some damaged frames and fill in the DV stream with some fake frames (copies of the last good, maybe). This, as I understand, what premiere is doing. If it is not possible to make this for dvgrab (w/o source code hacking) then is there a way to first capture with dvgrab and then import into premiere, asking premiere filling the gaps? I mean, I tried to do this but then premiere just neglects the gaps in timecode and I have as the result exactly what I had already after dvgrab.

To give some info: the result is reproducible exactly few times on two computers, so, it is not just some artifact of the setup; I have only one camcorder (the one used for recording) and have no way to try another one; other tapes however are played well, so I believe this is a damaged tape; I'm sure I excluded all hardware possibilities for errors, the hardware is not bloody new but adequate to capture DV.

Finally, googling did not help.

Thanks in advance for your help, guys,
Alex

[aedipuss]

try capturing with windv. set it so it only splits on greater than a 1 second discontinuity.

[Cornucopia]

What is your hardware chain? Just Dv cam -> Firewire -> Pc?

What shows up on the cam's viewfinder - garbage? freezing/stuttering? good image throughout (with maybe a cinch line rolling down during the bad parts)?

Might be a reason to do an alternate cap via composite and just replace the bad frames.

Scott

[alex-kas]

Thanks, aedipuss, for the advise. I gave it a shot and it goes. I did not do it before since I'm more linux oriented and premiere was just by product on my friend's pc.

This, however, does not mean I restored the video since it was damaged. It is way better, however, than after dvgrab. And, it is split in the correct way compared to premiere. And, yes, surprisingly, it is NOT some magic extrapolation by premiere! windv gets the correct number of frames, all 25/second, just, for example at some point frame number 1 and 5 are good, and frames 2, 3, 4 have the image from 1 and wrong timecode (either 1 or 5).

Thanks to Cornucopia for the reply. I should think about. My chain is: dvcam(panasonic gs500)->1394->PC. The cam has the A/V output but pc does not have an input ... Fortunately, I have only 2 damaged tapes but than it means I'm hardly go to obtain a card to capture something apart from 1394. The viewfinder reproduces what I have after windv or premiere capture.

A question about: what do you mean by "replace the bad frames"? Do you have a hint which software can identify the described timecode distortion and then replace fake frames with some extrapolation? Or at least, to identify those broken timecode spots? Because it is not 1-2 places, it is few peaces of 15 minutes of recording, roughly, 50 timecode distortions in each peace ... Some batch procedure is needed. Weired.

This, btw, happened to a pack of sony miniDV tapes. One more global question: why? I have a tape: 30' good, 15' damaged and then 15' good. Each peace was done separately but not that long time ago (1 year) and the whole time range recorded on the tape is about 2 weeks, i.e. it was not for years in the cam. Would it be magnetic field, heat, etc than all the tape would be damaged. The cam is the same. It worked before and works now. How come? I just want to be sure next time I record I do not get garbage.

Thanks, Alex

[fvisagie]

A question about: what do you mean by "replace the bad frames"? Do you have a hint which software can identify the described timecode distortion and then replace fake frames with some extrapolation? Or at least, to identify those broken timecode spots? Because it is not 1-2 places, it is few peaces of 15 minutes of recording, roughly, 50 timecode distortions in each peace ... Some batch procedure is needed. Weired.

I'm not sure what your level of experience is or how much these tapes mean to you, but there's a whole bunch of Avisynth tools dedicated to fixing bad frames and video repair in general (not that I have any experience of those myself). Something else that may be worth looking into is an Avisynth-based utility I made for identifying timecode discontinuities (looking for edit cuts in my case).

This, btw, happened to a pack of sony miniDV tapes. One more global question: why? I have a tape: 30' good, 15' damaged and then 15' good. Each peace was done separately but not that long time ago (1 year) and the whole time range recorded on the tape is about 2 weeks, i.e. it was not for years in the cam. Would it be magnetic field, heat, etc than all the tape would be damaged. The cam is the same. It worked before and works now. How come? I just want to be sure next time I record I do not get garbage.

When this happened with my camera, the cause was intermittent head misalignment. That in turn was caused by damage to the head mount, probably due to some kind of mechanical shock according to the repairman. He replaced the necessary part and it didn't cost too much. So I'd definitely have the camera serviced and checked if I were you.

Cheers,
Francois

[alex-kas]

I'll definitely look in avisynth, thanks for the point, fvisagie. My experience is not that great but I feel myself smart enough to follow some reading and discover things The camera will be serviced, no question in this but I have an impression it is good, since a bunch of tapes was filmed after w/o any glitch. Or at least I hope it is good since I cannot imagine finding a good place in Brussels to do the job. My overall experience about technical guys here is very bad

[fvisagie]

In a similar situation regarding workshops, I found the largest photo/video retailer in Cape Town (who also refurbishes and sells 2nd-hand equipment), and found out who THEY contract in turn for doing specialist service and repairs. This way I found myself an excellent German.

[Cornucopia]

If the viewfinder duplicates what you see after the capping, then the problem is most certainly on the tape, and bad enough that even the cam can't correct for it. So you have to face the fact that those missing frames are truly GONE. What to do?
1. Leave it as-is. (Using the premiere type version that has the correct framerate)
2. Use an AVISynth script similar to what fvisagie mentioned to find, and then correct - through interpolation - the missing/bad frames.

The replacement method I was hinting at would only have worked if your viewfinder output (should be mirrored by Analog out) were still GOOD, which it isn't in your case. So, never mind.

Good luck,

Scott

[Brad]

good image throughout (with maybe a cinch line rolling down during the bad parts)?

I have zero experience directly with MiniDV, so this is a genuine question: how would that happen? I would think damaged frames could only show digital errors.

[fvisagie]

I have zero experience directly with MiniDV, so this is a genuine question: how would that happen? I would think damaged frames could only show digital errors.

I'm not sure what you mean by digital errors, but error frames from my camera display partly with new lines and partly with old lines from the previous frame. Usually the new lines are the top ones, i.e. in scenes with movement you'd see horizontal tearing on the frame, with the top part moving from the previous frame and the bottom not.

@alex-kas, another utility I highly recommend you try is ScenalyzerLive. I recently started running into DV capturing problems on a new computer. Amongst others I evaluated all the capturing tools I could lay my hands on (I'd been using Stoik Capturer for years). If memory serves, ScenalyzerLive was the only one that 1) distinguishes between damaged frames and frames dropped for some other reason, 2) still captures the damaged frames, and 3) shows you at what timecode/frame count the drop or error occurred.

The fact that it still captures error frames and shows you where they are opens up many possibilities, like multi-capturing and accurately replacing error frames that were captured correctly on another pass, or even deciding to keep the frame if damage is negligible. Bear in mind that even frames with over-driven audio may be flagged as damaged apparently.

After trying all the usual cures like fast-forwarding/rewinding and so on, I'm currently experimenting with 'repairing' a damaged tape . It involves winding the tape to each error position, removing it from the camera, lifting up the cassette lid to expose the tape and blowing hard on it with a lens cleaner. I haven't finished yet to evaluate results, but I do have 2 fairly good multi-captures to fall back upon.

Good luck!

Cheers,
Francois

[SixFiftyThree]

I believe there are high-end DV decks that are better equipped to resolve drop outs and errors, particularly Sony models with the Dynamic Motion Control feature. This is apparently the go-to option when nothing else works. I bet a pro service would be using one of those, might be better just sending in whichever tapes can't be fixed by consumer means.