Odd audio dropout during capture.

farss wrote on 9/9/2004, 3:11 AM
Been capturing more hours than I care to remember of sports tapes to go our on DVD. Anyway decided to have a break from that and work on a short video to be converted to NTSC DVD needed in a hurry.
Anyway this client had me do this job before but didn't realise he needed a NTSC DVD for his clients in the USA to be able to view it. Previously as his VCR was out of action he bought over his hard drive, plugged it into my system and we were away, DVD done in less than an hour. Only problem was in about two places we had some really bad judders in the video, almost like dropped frames and Vegas was none two happy about the audio. I wrote it off to some oddity in his ULead software and how it wrote the AVI file.
So this time he prints the thing to tape and I start capturing it on my new DSR-11.
Now tape looks and sounds just fine on my 'monitor' but monitoring the audio thru vidcap there are some bad dropouts and yes they're in the captured file. But here's the truly wierd bit, they're in the same spot as we had trouble with the AVI I'd loaded from the hard drive last time.
Now I can probably get around this by doing another capture of the sound track only from the audio o/ps of the VCR and recording into Vegas and patching the missing bits in, it's only a demo tape so 100% perfection isn't a high priority.
But what the heck is going on? It seems, OK, his rendered AVI file had something really odd in it, that 'oddity' made it into the tape and is somehow screwing up either Vidcap or the digital circuits in my VCR yet the data stream is good enough for the VCR to decode it and produce good audio and video on the analogue outputs.
Man this is wierd, only reason I'm sweating on this a bit is this is a new client who already has a good market for his product so an opportunity not to be missed. I promised him to fix up a few things he knows is wrong in his editing but this isn't making the job any easier and I really need to get to the bottom of it before he gives me the real stuff to work on.

Bob.

Comments

farss wrote on 9/9/2004, 5:09 AM
So I recaptured just the audio via analogue and its 100%. Looking carefully at the footage the audio dropouts in the DV captured track last the duration of a clip and from what I can see it seems only to affect clips that have had some intense FX applied such as SloMo and the SloMo looks pretty bad.
Maybe I should take this to a ULead MSP forum!
But even if it has something to with MSP the question remains, how can it get onto a DV25 tape that plays out fine as analogue and yet VidCap drops the audio (or does the VCR loose it?). Could it be that the audio has become some unlocked that something in the chain gives up and drops it altogether?

So many questions and no real way to analyse it. I could try copying the tape via firewire to another VCR and see what happens I guess or I could just be glad I've fixed it up well enough and get on with it.
Except I'm going to be taking other videos from this guy and authoring them for DVD replication and I'm pretty certain there's also something very subtle wrong with the video and the mpeg encoder is going to have a dummy spit.

This is this guys first go at releasing on DVD, everything before was on VHS which is a much more forgiving format, if the duplication house was just going composite to composite from his DV master it probably would have looked OK.

Bob.
farss wrote on 9/9/2004, 2:50 PM
Bump!
No one maybe with some MSP background have any ideas on this?
farss wrote on 9/9/2004, 8:42 PM
Thinking all was now well I encoded this clip to mpeg-2 and onto DVD. Looking at it on a studio monitor all the 'untouched' footage looks perfect but something has gone seriously wrong in other sections. The SloMo footage stutters BIG time and there's one pan that looks a bit shaky in DV but totally falls apart on the DVD. I'll run it through a PC to check the bit rate, maybe its too high for the player but I don't think that's the problem. I'm more inclined to think something has gone wrong in the clients system giving effectively a situation where the entire frame is changing every frame and the encoder is simply unable to cope. It looks worse than it did last attempt where I'd used a two pass encode which might help explain it.
Still cannot really see how this got onto a MiniDV tape in such poor shape.

One suggestion I've had is that one of the pans has been reversed! This can cause nasty field order problems and certainly looking at it frame by frame on the Vegas TL the pan seems to advance two frames then go back one then foreward two!

Bob.