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5th August 2020, 11:32 | #1 | Link |
Broadcast Encoder
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Blackmagic DeckLink Audio out of Sync
Hi there,
I've been capturing a lot a tapes ever since I began the Remastering and Digitalization project and I'm using a BlackMagic DeckLink card, however I'm facing an issue now: every now and then there are dropped fields which generate orphan fields and make the audio go out of sync. I'm capturing as lossless 720x576 25i BT601 directly from the SDI output of the VTR, as suggested by Derek but sometimes when there are channel conditions or when the tape isn't playing smoothly, I get those horrible drops that make the audio go out of sync and I have to capture the very same tape again and again 'till it works. Do you have any idea why? It's particularly annoying 'cause I couldn't care less about drops, but at least I expect audio to be in sync... The Sony VTR is auto-referenced, which means that the reference SDI isn't connected to the Blackmagic card, could that be the problem? I thought it was because I was writing directly to one of our 35 TB RAID6 systems and that perhaps there were networking problems, but that wasn't the case 'cause I saved the file locally this time and out of 6 tapes, 1 still had out of sync audio due to dropped fields... Any idea why? Sample: https://we.tl/t-0EWmlA8Tgw You can easily see at TC: 0:00:25.600, frame 640 marks the beginning of the drops. There's the speaker talking and you may not notice it 'cause you can't see his lips, but believe me, audio gets out of sync from there on. Last but not least, I'm connecting the Reference to the BlackMagic card. I connected it from the BlackMagic Decklink card to the "Ref Video" of the VTR (Blue Cable). Did I do it correctly? And what about the 75 Ohm resistance inside? Is it needed or not? I mean, do I have to keep the switch on or set it to off? I'm sorry but VTR are really not something from my era. VTR without SDI output only: https://i.imgur.com/oRuLDjT.jpg VTR with the Reference SDI connected (top left, blue cable): https://i.imgur.com/H3HrlbY.jpg Blackmagic Decklink card with SDI input (green cable, left) and Reference (blue cable, right): https://i.imgur.com/tOa6TcA.jpg |
5th August 2020, 12:35 | #2 | Link |
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I'm not an expert and never used professional material but I believe a TBC could help (if you find one with SDI).
I noticed that when I put a standalone dvd-recorder between my camera and my capture card, the signal is much better, the video is more stable and there are much less dropped frames. I guess it has a built-in TBC which is quite good. |
5th August 2020, 15:00 | #3 | Link | |
Broadcast Encoder
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I just digged into old ancient documentations and apparently just like we manually use Bars-note to make sure our waveform monitors are working correctly and that our signal is in Limited TV Range during live events, that very same signal was used as "Reference" by old TBC to make sure levels were matching and that there weren't any dodgy things going on like sudden timecode changes and so on. I didn't know VTR were so clever. So now all I need to do is to bring the old SD bars-note reference to the office in which I'm doing the Remastering and connect it to the VTR so that it's gonna be referenced! |
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10th August 2020, 18:02 | #4 | Link |
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Just throwing this in:
https://forum.doom9.org/showthread.p...43#post1873943 https://forum.doom9.org/showthread.p...80#post1873980 boils down to: The Blackmagic Decklink Shuttle at least has no frame nor field TBC, just line TBC. If the Decklink has, you may deduct from your specs/PCB. Your video playback machine SONY DVW-A500P (a 35kg beast) should have all it needs to get the best out of analog and digital Betacam tapes. Maybe it is more than one TBCs involved and these interfere? I had that once in CVBS S-Video land.
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"To bypass shortcuts and find suffering...is called QUALity" (Die toten Augen von Friedrichshain) "Data reduction ? Yep, Sir. We're that issue working on. Synce invntoin uf lingöage..." Last edited by Emulgator; 10th August 2020 at 18:52. |
15th August 2020, 15:57 | #5 | Link | ||
Broadcast Encoder
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Same goes for the VTR, it's currently set on "Ref Video" and in fact the stop sign blinks as it's complaining that it doesn't have a reference connected. I already asked to bring the bars-note signal there, I hope they'll do it soon, but at the moment, I'm capturing without a reference. As to an external TBC, I don't have any. Should I purchase one or am I gonna be fine without it as long as the card and the VTR are referenced ('cause they have an internal one)? Quote:
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16th August 2020, 00:13 | #6 | Link |
Derek Prestegard IRL
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I don't believe a TBC is of any use when you're working with an SDI output. I think it's solely useful when capturing analog video, but I could be wrong about that
Even if you're capturing from an analog Beta(SP) your VTR will do a great job of digitizing it. The DVW-A500 is a monster . I.. A frame sync on the other hand is often useful, but generally not for cases like this, especially with short cable runs. If you have one laying around like an AJA FS1 it might not hurt to throw it inline... You shouldn't need to do anything more than connect SDI out from the VTR to SDI in on the capture card, plus an RS422 serial port for deck control if you care to use it. That should literally be it. I'd makes sure you're on the latest stable driver and firmware for your card to start. Also maybe use a different SDI cable just in case. Also, are you sure your local storage can keep up quite reliably with the video format you're capturing? Uncompressed 576i 4:2:2 10 bit is still like 220 Mbps, which isn't much, but may be a challenge if your disks are nearly full or there's other stuff happening on your system Try capturing into H.264 or something as a validation. Do you have a different VTR you can try with as well? As a last resort you _might_ get better results using a second VTR to dub to a fresh Digibeta tape, and then capturing that. Last edited by Blue_MiSfit; 16th August 2020 at 00:19. |
16th August 2020, 22:28 | #7 | Link | ||||
Broadcast Encoder
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Yeah, it really is xD Quote:
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Well it only happens once in a while, so it's really hard to spot. For instance, it happened several times during the hours-long Agassi vs Ivanisevic tennis game, but only 1 time on 24 episodes of "Juke Box" which last 30 minutes each. I could leave it to record something for several hours and see if it loses the sync, but still... As to the CPU is generally 12% when capturing in lossless uncompressed yv16 8bit 'cause it isn't something intensive... (it's a very old 4c/4th Xeon with 32 GB of RAM, but it seems to deal with it just fine). Speaking of which, I'm capturing in 8bit which is 160 Mbit/s; do you think 10bit would really be better given that the content doesn't really have much detail or critical gradients? I mean, banding is literally the last of my problems on those tapes full of spots, scratches, raimbowning, dot crawl, grain and many other things... I mean, should I change and capture in 10bit instead? Plenty of them (where plenty is a number ranging from 35 to 100 'cause some of them may or may not work anymore), but I would need to see if they're working and carry them all the way up to the third floor where I'm currently located... and it's summer... I don't wanna make my life miserable again by sweating the hell out of my shirt, carrying a 77 pound beast from -2 Building 1 to the 3rd floor of Building 2 xD |
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18th August 2020, 19:28 | #8 | Link |
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If I had such a wealth of playback machines:
I would have like 4 set up, swap machines as I find dropouts and have at least 2..3 good captures per source left. And have fun with the exhaust of those 2kW X-}. A bit safer than having someone finding faults later in the process and blaming the capture guy. Are those orphaned fields at the same place everytime ? One machine may find its way better than another. ...And well I may be in the queue for a working machine for the few beta tapes I will have to capture myself. Around 250 to 450.-€ for a DVW-A500 now.
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"To bypass shortcuts and find suffering...is called QUALity" (Die toten Augen von Friedrichshain) "Data reduction ? Yep, Sir. We're that issue working on. Synce invntoin uf lingöage..." Last edited by Emulgator; 18th August 2020 at 19:31. |
20th August 2020, 02:40 | #9 | Link |
Derek Prestegard IRL
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Yes, you should do everything in 10 bit 4:2:2 these days unless you really don't care Minimize those format conversions, keep everything SDI compatible.
Any chance you could try a different computer in case it's some weird bus latency issue? I've seen problems relating to unstable capture on certain motherboards and had to disable bits of integrated crap or just use a different board alltogether. These types of issues can also cause latency / other problems in audio production apps. Believe it or not, this is one area where Apple generally does a very good job. |
20th August 2020, 17:42 | #10 | Link | |||||
Broadcast Encoder
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As you can see, the difference is ENORMOUS. I never expected Sony DVW-A500 to be so good, but apparently it really is, so hats off and a big fat "thank you" to Sony Engineers from the 70s/80s for their incredible electronic work. Quote:
EDIT: Oh, look at that, my 1'000 post on Doom9! I'm moved! :') Last edited by FranceBB; 20th August 2020 at 17:44. |
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21st August 2020, 08:46 | #11 | Link | |
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21st August 2020, 09:49 | #12 | Link |
Broadcast Encoder
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A capture...?
Oh you mean a screenshot! Sure thing! Thompson VTR on the left, Sony VTR on the right: As you can see, the Thompson VTR makes no effort at all on trying to compensate oxide fading occurred on the tape and it just outputs what it reads. Besides, in the parts in which the tape is completely ruined, it doesn't do any kind of smart correction using adjacent fields or anything, it just outputs crap. This includes, stuttering, shacking, channel conditions and some scenes in which there's chroma only but almost no luma at all for whatever reason, while the Sony VTR makes a HUGE effort in trying to compensate the deteriorated tape in the best possible way and if it's really completely spoiled and it can't read anything, it just outputs a duplicated field from the former one. |
21st August 2020, 11:43 | #13 | Link |
Big Bit Savings Now !
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Just downloaded your .mov sample.
Remarkable difference ! Many thanks for that comparison. That particular Thompson machine seems to be just defective, beside the tape-introduced artifacts I see AGC/PLL pumping heavily already in sawtooth manner within the colorbar intro. BTW, I see progressive frames, where has the interlacing gone ? Ah, I see, 50fps. You uploaded your results post QTGMC, I guess.
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"To bypass shortcuts and find suffering...is called QUALity" (Die toten Augen von Friedrichshain) "Data reduction ? Yep, Sir. We're that issue working on. Synce invntoin uf lingöage..." Last edited by Emulgator; 21st August 2020 at 11:49. |
21st August 2020, 11:55 | #14 | Link |
Broadcast Encoder
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Yes, it would have been a mess to make a side-by-side comparison keeping the original fields.
Not really. Those colorbars were recorded in the tape, they were not generated by the Thompson itself, so you can imagine that the problem was kinda persistent across the whole tape. As to the VTR being defective, it could be if it wasn't for the fact that I tried a Digital BetaCAM from 2007 on it and it played just fine. I think Thompson engineers only cared about Digital and didn't really pay much attention on the Analog counterpart which was older, so they limited their VTR to just play what was on the analog tape without any kind of adjustments. They probably thought that Digital BetaCAM were "the future" and focused on them only. Last edited by FranceBB; 22nd August 2020 at 02:32. |
28th August 2020, 10:28 | #17 | Link |
Broadcast Encoder
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Derek, out of curiosity, we're ready to move from the one with a single SDI (which was effectively a test) to the one with 4 SDI + a Reference.
The only thing I'm wondering, though, is: is there a way to remote all 4 VTRs connected to it? 'cause it looks like we can use 4 SDI but only remote 1 VTR, which isn't really ideal... Last edited by FranceBB; 28th August 2020 at 10:43. |
29th August 2020, 01:45 | #19 | Link | |
Broadcast Encoder
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I was looking at the card you suggested but it seems that I can't have a deck control for them all. I would really like to avoid to monitor 4 VTRs at the same time as I would rather pick the starting and ending timecodes and let them run automatically... |
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29th August 2020, 08:19 | #20 | Link |
Big Bit Savings Now !
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The Sony DVW-A500P user manual mentions the control panel BDKW-515 which can control 2 machines
and the Parallel Interface Kit BDKW-509 (50-pol (Centronics ?) cable). If equipped, maybe you can use that to hook up 4, at least 2 DVW-A500P machines in parallel...
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"To bypass shortcuts and find suffering...is called QUALity" (Die toten Augen von Friedrichshain) "Data reduction ? Yep, Sir. We're that issue working on. Synce invntoin uf lingöage..." Last edited by Emulgator; 29th August 2020 at 08:22. |
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