Sound/video desynchronization in playback
 

Hi,
First of all, excuse my English, I hope I'll be understandable... I have a mixing auditorium with :
- Avid S4
- Avid MTRX in video ref
- Avid NEXIS
- MacPro with macOS Catalina
- Blackmagic Design Decklink Studio 4K
- MUTEC iclock dp (video ref)
- JVC video projector

I explain my problem to you, I work with a sound engineer for film mixing and here is the history of what happened :

First thing a little bit strange...
- Copy of the video on the NEXIS, copy session on intern SSD and opening session : ProTools frozen on opening without error message, nor milling...
- New session, import session data : same
- New session, import session data without video, and import video on NEXIS in a second step : PT OK

Here the big problem... :
Sound/image desynchronization on a continuous reading (8 to 12 de-synchronizations suddenly on a 1h50 reading)

Buffer size: 1024 samples
Delay Compensation : On
I restart iclock + MTRX + Mac : same result.
I uncheck GPU Enable in ProTools preference : same result.
Test with an Apple ProRes 422 video, Apple ProRes proxy, DNxHD video: same result.
I tried to pass the video track from FULL Quality to 10bit quality then to Draft : same result.
I can open the Decklink Video Setup preferences from the video track in ProTools, and the video ref is locked to PAL.
Changing the Decklink Video Setup “default video standard” setting to 1080p50 instead of 1080i50: same result.

I tested with another session, another film: everything works fine
Test in sound editing (mac mini) : work fine, so the codec video is fine.

Another problem maybe related...
Video doesn't start sometimes when starting playback, it remains frozen, it starts on the second playback start.

When the video freezes on the videoprojector, it also freezes in the video window of the PT (cmd+9)

I would like to Update 12.2.2 of the Decklink 4K Studio: would correct a problem preventing the synchro start of playback but not Catalina compatible and therefore protools...

Can iClock be at fault? Settings rather vague on the SD/HD settings... Not a lot of menus... but the settings/connections seem coherent.

Globally, I have big doubts about the Blackmagic video capture card...

Do you have any ideas ?

I remain at your disposal for any further information. Thanks in advance everyone !!!!

LST

Re: Sound/video desynchronization in playback
 

I’m not sure the iClock is doing anything for you. I don’t think Pro Tools will lock to any video ref except Sync HD or Sync X.

Even without video sync there should be no drift. Only a slight sync offset for every play. But Decklink cards especially with older Blackmagic software were notorious for random sync drift. I’m not sure which versions are acceptable. Hopefully somebody else can chime in. I switched to Aja.

That still does not explain Pro Tools freezing upon loading video from Nexis. There can be some stuttering and dropped frames if it is a high bitrate video and your bandwidth is suffering. I don’t know what could cause the freezing though. Do you have another SSD so you can play video locally?

Re: Sound/video desynchronization in playback
 

Thank you for your response. For me, iClock is a Ref Video HD.

I can try to play the video on another SSD locally, indeed. But I don't think it will be better.

But yes... I think that AJA would solve all my problems...

Re: Sound/video desynchronization in playback
 

As been said:

Without a SYNC HD or SYNC X your ref generator is not going to do anything. It might be feeding a clock to your video card but PT won't lock to it without a SYNC interface attached and set to video ref.

But it sounds like you are using a PAL sync signal (old school black burst) for the BM card or did I misunderstand?. Just asking because when running HD the card wants to see a trilevel HD sync signal, so maybe that's cause your problems? Just a thought. I think your MUTEC box is an old black burst generator, no? If yes I would disconnect that entirely and try again.

Re: Sound/video desynchronization in playback
 

having suffered similar issues I found Video Sync by non lethal applications very useful - you can try it for free for 14 days

may solve your problems.

Re: Sound/video desynchronization in playback
 

Thank you for your response.

So, for you MUTEC iclockdp is useless ? Indeed, the clock uses a PAL sync signal for the Decklink BM and you're right... in Session setup ProTools > Sync Setup > no avid synchronization peripheral present.

The link for the iclock manual : https://www.manualslib.com/manual/13...ec-Iclock.html

Here are the iclock settings (generator sync) :
VIDEO OUT1 & VIDEO OUT2 :
REF : INTERN
FORMAT : PAL
VIDEO TYPE : BLACK + BURST
SD/HD Video Out 1 is connected to MTRX
SD/HD Video Out 2 is connected to BM Decklink Studio 4K

Here are the DADman (MTRX) sync. settings : LOCKED
Sync source : Video
Sync out : Work Clock
Sync term : High Z
Digi dli (smpls) : 5

I did a lot of other tests today.

1_try to switch "REF : INTERN" to "REF : HD-P-1"

2_completely disconnect the MUTEC iclock and switch to the DADman (MTRX) sync source in "internal" mode, instead of "video ref"

3_increase cache size to 54GB instead of 40GB in playback engine (ProTools)

4_disable compensation delay in Pro Tools

5_Desktop Video Setup 12.2 not being Catalina compatible. I close Pro Tools, uninstall Desktop Video Setup 12.1, and downgrade to 11.7

I still have to try to play the video on another external SSD and try Video Sync by non lethal applications, but I'm starting to despair. I feel like I'm going to have to change the iClock to a SYNC X and change the BM to an AJA !

Thank for your help !!

LST

Re: Sound/video desynchronization in playback
 

It's not a useless device per se but in your setup it's not doing anything because it's an old black burst sync clock which is useless for a workflow using HD video (so basically everything done nowadays). And PT will only frame lock with an AVID sync attached.

You will need a TriLevel sync clock generator like a AJA Gen10 or Nanosyncs plus an AVID SYNC HD or an AVID SYN X (which essentially if a SYNC HD with built in clock generator).

My theory is that the BB that you are feeding to your BM card is tripping the card so my tip was to remove the Mutec from the setup, clock internally and then try again what happens. Unless the BM 4K can cross-lock between PAL BB and HD video. The Decklink SDI that I have can only lock the same format as the video. So maybe I am wrong there. Not sure.

Ultimately your old back-burst box is a "door stop" in a HD video based setup I think.

Sorry to say.

For what it's worth: I'm using BM driver 11.4.1 (the last one compatible with Mojave) with the below setup and picture works flawless and is sync. No drift or other issues.

Re: Sound/video desynchronization in playback
 

But remember: If your setup has problems running video in a stable way even without any sync clocks attached, the clock and sync box won't help. The latter will only make sure everything is sync. Even without the sync gear the video should not freeze obviously.

Re: Sound/video desynchronization in playback
 

With your investment in the console, Matrix, and Nexis I think you really should plan to get a SyncHD or Sync X. There is no way to ensure absolute sync without and with large scale mixing you need it.

HOWEVER I agree with Frank. You'd need to finish trouble shooting the video playback first. Definitely using only the Matrix internal sync and local video would be my first step. That removes all external factors.

What version of Pro Tools?

Re: Sound/video desynchronization in playback
 

hi,

sorry for my late reply... I try some stuffs...

As a reminder, here is my initial workflow :
ProTools 2021.12 / macOS Catalina
Video played on the NEXIS, ProTools session in LOCAL disk.
The MTRX and the Decklink BlackMagic are powered by the MUTEC “SD/HD Video Out” outputs (PAL signal, Blackburst).
The DADman is well locked in video ref, and the ProTools video track gives access to the output settings of the BM card: "Locked PAL (SD)"
The video provided by the client is a ProRes 422, 25fps (clock and ProTools project at 25fps as well).

TEST 1: Disable GPU in ProTools preferences ❌
TEST 2: Deactivate the compensation delay ❌
TEST 3: Increase cache size from 40 to 56GB ❌
TEST 4: Deleting ProTools preferences ❌
TEST 5: Switch the ProTools video track from Full Quality to Draft ❌
TEST 6: Video transcoding of the client's video in ProRes422 HQ ❌
TEST 7: Video transcoding of the client's video in ProRes422 proxy ❌
TEST 8: Video transcoding of the client's video in ProRes422 i ❌
TEST 9: Video transcoding of the client's video in DNxHQ ❌ (3 desynchronizations over 1h50 of film instead of 8 to 12).
TEST 10: Video transcoding of the customer's video in DNx36 ❌
TEST 11: Switch the clock internally (mutec off, DADman in internal source sync) ❌
TEST 12: Connect the MTRX and the BM to the MUTEC in Word Clock and change the source sync of the DADman to word clock ❌
TEST 13: Go back to Decklink BM driver 11.7 (the higher version is not compatible with macOS Catalina) ❌
TEST 14: Replacement of the MUTEC by an AVID SYNC X in video ref and in word clock. DADman/ProTools/Decklink locked in HD ❌
TEST 15: Instead of playing the video on the NEXIS, play it on another external SSD ❌
TEST 16: Opening another project with video exported directly from DaVinci Resolve Studio in DNxHD36, then imported into ProTools ❌ (1 desync on a 1h20 film)
TEST 17: Exchange of BM card with that of the calibration room (BM Decklink 4K Extreme 12G) ❌
TEST 18: Playing video from an external drive (LaCie Big6 Thunderbolt 3) connected directly to the MacPro ❌
TEST 19: Opening sound editing sessions on a Mac mini and in the mixer's home studio ✅

I had several technicians/mixers/trainers on the phone who advised me to stop with ProRes anyway and to work only in native AVID format, and to favor work on two discs in LOCAL (1 for the video and 1 for the ProTools session), but that doesn't solve the problem.


Findings:
- The clock problem would be surprising because the SYNC X don't fix the problem.
- It is not a session problem because it is transferred to another project and it is read without worries on a Mac mini.
- This is not a reading problem on the Nexis, because the problem appears with reading on an external disk in Thunderbolt 3.
- This is not a codec problem but DNxHD still causes less synchronization than Apple ProRes.
- It is not video card problem because the Extreme 12G postpones the problem. Is an AJA card a solution?