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Jim_C  
#1 Posted : Monday, March 25, 2019 2:35:55 AM(UTC)
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The issue is that the analog audio Line In to vMix will, with no warning, start stuttering, or cutting in and out on about 1/2 second intervals, through the HDMI external output. Video is fine.

If I were to play a video from vMix while the Line In audio is stuttering, the recorded audio is fine.
The NDI connection carrying the same feed between the same machines does not stutter.

Closing and reopening the audio Line In will fix as will restarting vMix completely.
Closing/reopening the external or reseating the HDMI cable does not fix.
The stuttering audio is received by all software on the recording PC so it's not one in particular.

Anyone have ideas where to troubleshoot? It's hard to duplicate as it starts randomly.
All drivers are up to date.

I know using the 3.5mm Line In on the motherboard is not ideal but I have several vMixs in the field using this method and never had this stutter issue.

I've attached a simple diagram of the setup. Thanks for any direction one might have.

EDIT: I only turned on the NDI to test if it also stutters when the HDMI does. The actual setup is HDMI only.


Signal Flow
mgrayeb  
#2 Posted : Monday, March 25, 2019 4:37:30 AM(UTC)
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I wonder if the 3.5mm port is the issue. Is it one of those combo headphone/microphone ports? I've had trouble with those periodically in the past and switched to using a USB audio dongle without issue since: https://www.amazon.com/S...+%2Caps%2C131&sr=8-7

Not sure if that is relevant in this case or not.
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Jim_C on 3/25/2019(UTC)
Jim_C  
#3 Posted : Monday, March 25, 2019 5:01:50 AM(UTC)
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Hey, thanks for the input.

It's a dedicated Line Level In but it is a 3.5mm yes.

I think the fact that the audio in the NDI output is fine points to something going with the embedding of the analog into the HDMI external output signal.

Audio input must be fine in the circuitry as its OK in NDI and also the meters on the Line In do not show the stuttering, they are OK, but meters on the recording PC are flshing on and off with the signal.
Jim_C  
#4 Posted : Monday, March 25, 2019 5:20:48 AM(UTC)
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I've got 3 days before next gig to figure it out and at this point unless I can replicate and fix I believe my options are:

1 - Cross fingers and hope it doesn't happen as it will go hours and sometimes a full day and not happen.

2 - Use NDI into recording PC but that scares me as we also auto transfer the recorded files from the vMix and the recording PC to a NAS as soon as they finish (every 3 minutes). So guessing I would want to throttle those transfers.?

3 - Embed the audio into one of the camera's SDI signal and use it from there.

4 - Use some type of external sound card/device/mixer and come in USB as gray mentioned.



sinc747  
#5 Posted : Monday, March 25, 2019 7:09:23 AM(UTC)
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Had a similar problem several years ago, ended up being a motherboard in the process of failing.. Hope that's not the case for you.

- Tom
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Jim_C on 3/25/2019(UTC)
raugert  
#6 Posted : Monday, March 25, 2019 7:31:25 AM(UTC)
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Does the HDMI embedded audio stutter if you disconnect the NDI feed ?

I looks like you have two simultaneous embedded audio sources in your recording PC carrying the same signal on (NDI and HDMI). Could it be something in OBS that is not decoding the embedded audio properly from the HDMI stream when the NDI stream is active and contains the same audio. Just a thought...
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Jim_C on 3/25/2019(UTC)
Jim_C  
#7 Posted : Monday, March 25, 2019 8:45:48 AM(UTC)
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Originally Posted by: sinc747 Go to Quoted Post
Had a similar problem several years ago, ended up being a motherboard in the process of failing.. Hope that's not the case for you.

- Tom


Hey Tom,

eeegaad, I hope so too. System is only a couple months old and only used in the field 3 times.


Originally Posted by: raugert Go to Quoted Post
Does the HDMI embedded audio stutter if you disconnect the NDI feed ?

I looks like you have two simultaneous embedded audio sources in your recording PC carrying the same signal on (NDI and HDMI). Could it be something in OBS that is not decoding the embedded audio properly from the HDMI stream when the NDI stream is active and contains the same audio. Just a thought...



Thanks raugert,

I should have mentioned in the OP but I am only using the NDI now as a test to see if it stutters when the HDMI does. Originally when the problem began it was just the single HDMI connecting the machines. Once when it was stuttering (hdmi only, no NDI turned on) I opened up Flash Media Live Encoder and it was receiving the bad audio also.

I have no real knowledge to base it on but my gut is telling me something is losing timing or "glitching" out in the embedding of the analog audio into the BM Intensity card for output. Closing and reopening the Line In input resyncs it. Or something. :/

If I could reproduce it easily I would probably start playing the BM driver shuffle. But so far it's been running all day with no issues.


Jim_C  
#8 Posted : Monday, March 25, 2019 11:48:12 PM(UTC)
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Well it started doing it sometime overnight with no interaction on either machine.
Here's what I know.

-The 'stutter' is in the HDMI audio output of the vMix but not the NDI.
-The issue is only in the audio Line In of the vMix, playing videos or other sources are fine in the HDMI audio output.
-It is not being caused by the Osprey capture card as I plugged the vMix Intensity Pro output directly into an HDMI monitor and you can hear it on the monitor.
-I used FMLE to record the external output of the vMix on the vMix machine itself and it is clean.

So it definitely seems like an interaction with the analog audio input, the vMix and the Intensity Pro 4k card somehow. If I were to close the Line In and re-add it I bet it would be fine, but I kinda want to leave it broken for a while to try and troubleshoot. Troubleshoot what I'm not sure, but if I fix it it could be minutes, hours or days before it breaks again.

Jim_C  
#9 Posted : Wednesday, March 27, 2019 12:15:40 AM(UTC)
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The plot thickens.

The HDMI output of the BM Intensity Pro 4k is being sent MA audio.
The Line In audio is routed to Bus A output only.
Bus A output is routed directly to the BM card.

Stuttering happened again overnight HOWEVER if I change Line In to send out M instead of Bus A, the BM card sends it cleanly.
M = Clean Audio
A = Stutter
M+A = Both clean and stutter.

My earlier finding that videos played internally where fine and that it was ONLY the line in stuttering is wrong. The reason they played fine is that they were defaulting to M out to the BM card. Which is clean. Once the stutter starts on Line In, if I play anything thru A it stutters out the BM card, but playing it out M is fine.




external1

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admin  
#10 Posted : Wednesday, March 27, 2019 12:34:24 AM(UTC)
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Hi,

Blackmagic devices only support outputting audio via one method at a time reliably. So using both Audio Outputs and External Output is likely the cause if the issue
so disabling the Blackmagic Speakers assignment in Audio Outputs is strongly recommended.

Regards,

Martin
vMix
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Jim_C on 3/27/2019(UTC), sinc747 on 3/27/2019(UTC)
Jim_C  
#11 Posted : Wednesday, March 27, 2019 2:45:28 AM(UTC)
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Woohoo! Thanks Martin!

Since Line In comes from FOH and the Master Out out goes back to FOH we were using that setup as a mix minus, but I'm sure there is another way to skin that cat.

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