Jump to content

Decklink Duo & No Latency from CPU's PCIe Lanes

Thomas Leong

Recommended Posts

Instead of furthering the question of latency from the Decklink Duo inadvertently diverted within another discussion

( http://forum.dataton.com/topic/1617-blackmagic-decklink-duo-problems/ )

thought it would be better to start a fresh one here.


Recently, I used the Decklink Duo and noticed no latency between the live IMAG video and the stage mics on the LED panels used. To date, I have not received a reply from the audio guy as to whether any audio delay was used. Personally, I doubt if audio delay was applied since -

1. It is not usual in my country for the audio desk to be so equipped unless specifically asked for BEFORE equipment is brought to the venue, and in this case, the venue was about 1 hour away from the city up in a mountain casino resort; and

2. As I was only present as a consultant to Watchout, any latency involving Watchout's use would have been referred to me to solve as the operator/user is new to Watchout, and no such questions were raised during rehearsals and showtime (by final client, the event organizer, nor anyone else).


Here are the installation facts:

Watchout Production PC: Mac laptop running Bootcamp; no live video feed; used built-in webcam as guide.

Watchout Display PC: ASRock Z97 Extreme6 motherboard, i7 4770K at 4.2GHz, 16GB 1600MHz RAM, ASUS HD7970 Matrix Platinum graphics card with 4 of the Display Ports used to output to the LED's Processor-Sending Card. HD7970 occupied the first x16 slot; Decklink Duo occupied the second x16 slot, but since this was a Z97 + 4770K, the 16 available PCIe 3.0 lanes were re-distributed to x8/x8 for both slots.

Live Video: Decklink Duo with only 1 input used, fed by a DataVideo mixer via a 100m cable (3 Sony cameras to mixer)

Result: I did not see any latency. Neither did the Watchout operator when I pointed out that there was no latency, and he concurred.


Question: Could it be that, in our case above, because the Decklink Duo was installed in a slot with lanes direct from the cpu rather than from the PCH, there is significantly less latency than should be expected, to the extent that the human eye cannot detect the latency, if any.


I do not have a SDI camera to test. If someone who has, can test and report back, it would be appreciated. Try a PCIe 3.0 slot that has lanes direct from the cpu rather than from the PCH (Platform Controller Hub; a'ka Z87, Z97, X79 or X99).


Thomas Leong



Link to comment
Share on other sites

  • 6 months later...

Yes, but need tests to confirm. If you have the equipment, please test with a PCIe 3.0 slot versus a 2.0 and appreciate if you can report back.


Additionally, with the new Z170 chipset, the pch (platform controller hub; read: essentially motherboard) now has 20 PCIe 3.0 lanes instead of 8 PCIe 2.0 for its peripherals, and a new higher speed DMI 3.0 communication link between the cpu and the motherboard peripherals. The Z97 and X99 use DMI 2.0.


How these new developments affect latency in live video capture need tests and feedback.

Link to comment
Share on other sites

  • 2 weeks later...

How distant was the stage from the place you was looking at the screens?

The sound is not so quick (approx 343 m/s).

If you was at 50m from the stage the sound reached you with a delay of approx 146ms, equivalent to 3.46 video frames @25 fps.

Maybe the natural intrinsic sound delay was just matching the delay introduced by vision mixer and decklink at your point of observation...

Link to comment
Share on other sites

  • 2 months later...

Hi Everyone

I have a 4 FHD projector setup. Video in the timeline is WMV9. originally a 4k video but i divided it into 4 parts as individual video files and played simultaneously in the timeline. I have SDI input in decklink at 1080p25. Along with that, I have a PPT captured through Datapath.
Im having a delay in Camera IMAG in watchout. Im using 
motherboard- Asus P8-z77-v LK
Intel i7 3.5GHz 3rd gen
16Gb ram
Datapath VisionRGB-E2S
Decklink 2k studio
Nvidia nvs 510 2GB
Watchout 5.5.2
Normally, there is a delay which is very minimal but the delay i experienced in this particular situation was about a quarter to half of a second and it varies from time to time. I tried to offline and re-online during the show and the problem still occurs. it happened to me twice with the same camera team. 
Can you please give me an explanation to this, is this really happening? And how can I prevent it from happeninga again? What could be the cause of this?
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...