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Feasibility of using vMix for live events
Rank: Newbie
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Joined: 11/14/2012(UTC) Posts: 2
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Hello,
Please forgive me if this answer has already been answered, but I am considering putting together a system for doing live productions using vMix and the following hardware:
Motherboard: Asus P9X79WS CPU: Intel i7 3930K Sandy Bridge RAM: 32 GB G.Skill Ripjawz DD3 2400 (PC19200 Unbuffered) Video Card: GeForce GTX 670GC 4GB 256bit GDDR3 Main Drive: Plextor M5P PX-512M5P 512GB SATA III Additional Drives: Hitachi 3TB SATA drives Video Capture/Output: BlackMagic Design Decklink Quad
This will be used in a live production environment mostly for speeches/presentations etc. with 3x Sony EX3 HD cameras normally.
My question is, what kind of a delay if any would I expect from a system above? If it is the stated 2 frames, then that shouldn't be a problem. However, I think our audiences will have a real issue if what they hear and see is out of sync.
Any advice and help is appreciated here.
Thanks in advance!
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Rank: Advanced Member
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Joined: 8/23/2012(UTC) Posts: 71 Location: Bangkok
Thanks: 1 times Was thanked: 2 time(s) in 2 post(s)
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Hi,
My system is quite similar in specifications, except for that graphics card, where I use a ATI 7850 and my MB is a Gigabyte Sniper
The vMix is configured for output using the 4th channel from the Decklink Quad as well as the HDMI output from the ATI card.
I found the following results: When using the internal graphics of my MB for the application screen , the delay on the Quad output is approx. 0,3-0,4 seconds, so between 8 and 9 frames on PAL input.
I found improvement when using only the ATI card for the application (On DVI) AND the output using the HDMI connection and then the latency dropped to about 4-5 frames (0,2 sec.). In the BIOS I disabled the use of the internal graphics. The Decklink Out was still a bit slower between 5-6 frames.(0,25sec)
I measured this by placing the iPhone in front a lower corner of the LCD screen and then recording this with the EX-3,with the feedback that it will create: you can make a whole string of iPhones with the stopwatch running on the screen. Record this for some seconds and then playback and pause. You can easily see and count the "round-trip duration"
But we have to take into account that even the output of the EX-3 as well as the input of an HD-screen might introduce a small delay, probably 1 frame or less but it still adds up in the whole chain. HDMI to SDI converters can also have their own delay. According to Martin, the Decklink might also buffer 1 or 2 frames before sending it out again, which might explain the small increase compared to the HDMI output.
All in all I think that Martin's claim of approx. 2 frames delay introduced by vMix could be correct: EX-3: 1 frame vMix: 2 frames HDMI-SDI: 1 frame LCD: 1 frame
Total 5 frames...... That seems to me the minimum possible, but I love to hear about other's improvements.
Oh, this is only the video delay, I have not research the audio yet.
Rob
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Rank: Newbie
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Joined: 11/14/2012(UTC) Posts: 2
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Rob,
Thanks a bunch, this is exactly what I was looking for. The numbers that you have posted are somewhat comparable to a For-A Hanabi HVS300HS mixer that goes for around $15K here in the USA with only 4-inputs, each expansion board is around $2K on top.
This is a bit of a gamble, but I think I will just have to try this out and see how its received. The slight delay may be worth the quality and features that we get in the end with my proposed setup.
Thanks again for posting this, it was a great help!
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Rank: Advanced Member
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Joined: 8/23/2012(UTC) Posts: 71 Location: Bangkok
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I tested the low latency option today with the newest software release and found that there is indeed a slight improvement in the total delay. When the low latency setting is selected and the program restarted I found a total delay of approx. 0.17 seconds, that translates to 4.25 frames on 25P, while in the normal mode it is 0.2 seconds = 5 frames @ 25P. With al the conversions going on from SDI-in to SDI-out I think that is perfect.
we still have to take all the other steps into account: Camera EX-3: 1 frame vMix: 1 to 1.25 frames converter HDMI-SDI: 1 frame LCD screen: 1 frame
So I think overall delay cannot be much less then 4 frames ( 16 millisec) from origin to display.
I am quite impressed!
Now if only I had a job for this machine.....
Rob
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Rank: Advanced Member
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Joined: 6/29/2011(UTC) Posts: 311 Location: Florida Thanks: 6 times Was thanked: 33 time(s) in 32 post(s)
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Other systems I have worked with accomplish low latency by not completely bringing the video signal in to the computer but rather use an external switching router which the software controls. I have had this though for a while now. What if vMix could not only switch between onboard cards but also control a external router switcher such as the BMD video hubs. Probably should put this in the feature request area :-)
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Joined: 1/28/2013(UTC) Posts: 6 Location: Slovenia
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I have exactly the same problem with latency. However my measurements are different (measured at 30fps).
The camera(Sony NX30)adds 2 frames of delay, the vMix another 4-5 frames. Capturing without audio reduces delay by 1 frame. Adding Blackmagic SDI external output adds another 3-4 frames. All together 10 frames or more, I got variable results.
HDMI to SDI converter only adds a few lines of delay, as there is no real conversion, uncompressed video is just repackaged.
I could live with 6-7 frames of delay, but once BM output kicks in with 3-4 frames or more it is just too much. I tried to use DVI output from graphic card but the video quality is not good enough (vertical tearing). It looks much better on the SDI output. Maybe is time for a switcher control, as Egriswold suggests.
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Joined: 1/13/2010(UTC) Posts: 5,228 Location: Gold Coast, Australia Was thanked: 4332 time(s) in 1528 post(s)
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Hi Peter,
The tearing you describe on the DVI output can be eliminated by using Windows 7 in Aero mode, or Windows 8/8.1 Also make sure the refresh rate of the second output is the same as the first in the Windows display settings.
Regards,
Martin vMix
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Rank: Member
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Joined: 10/8/2013(UTC) Posts: 20 Location: Australia
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Would it be feasible to consider adding a slight delay effect to the actual audio at the live event? Not so much that the audience would notice, but enough to lessen the gap between the audio and video feeds?
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Rank: Newbie
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Joined: 1/28/2013(UTC) Posts: 6 Location: Slovenia
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Hi Martin,
thank you very much for your Aero suggestion. It works indeed, tearing is gone completely, and those nasty spikes also.
Another good news is that when I connect Sony LCD TV to Nvidia GTS450 DVI out I have the option to select 50 HZ for Sony in Nvidia settings. Now even camera pan is smooth. This was not the case with computer LCD display with no EDID.
Peter
Jup, it is quite common to insert audio delay to reduce the gap, perhaps 30-50 msec. You can buy a cheap Behringer delay line for that and insert it into PA line. Additionaly, if the audience is at least 10m from the screen, there will be another 30 msec of delay and the gap will be even less.
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