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Blackmagic io questions

Discuss graphics hardware, computer hardware, and input/output devices to use with TouchDesigner

Blackmagic io questions

Postby monty_python » Tue Jul 02, 2019 8:54 am


I am using Touchdesigner (2019.16600) with Blackmagic io devices and have few questions.

1. Is there a way to somehow minimize delay of input video stream? Utilizing Nvidia Direct transport I am seeing delay of approximately 8 frames (when using 50fps). In video normal_state.mov are four Ultrastudio 4K Extreme 3 devices. Bottom one is outputting SDI signal which is sent as input to top 3 devices. Is there anything that could be done in order to lower delay visible on input? In my tests also other Blackmagic io devices performed similarly to these results. Does someone know if other io devices (such as Aja) have smaller delay?

2. All other attached videos have the same setup, except the fact that I disable and back enable output from top 3 devices in Toughdesigner (by setting active toggle in all three Video Device Out nodes to off and back on). When Touchdesigner starts-up, top 3 devices are in sync. However when I disable and enable their outputs, they randomly get different delay per device (as you can see in random_delay.mov). It is kind of unfortunate in scenarios when outputs must be in sync. Outputs could always be synced by closing Touchdesigner and opening it back up, but it would be great if disabling and enabling output won't make outputs asynchronous.

3. Outputs on top 3 devices get flipped halframes randomly. There is a 50% chance to get them right and also to get them wrong. This could be seen on random_flipped_halfframes.mov. This is directly related to SDI input from bottom device, as it is outputting interlaced signal. When Video Device In has deinterlacing enabled and set to Bob (Odd) this never happens (since input is deintarlaced and therefore output is always correct). However I guess it should work stable even when input signal is interlaced right? I guess it is not completely correct to sometimes get clean output and sometimes choppy output (due to flipped halframes). Again this is not an issue due to possibility to deinterlace, it is just something I noticed and thought developers might be interested in taking a look at why it behaves in such way.



[ Play Quicktime file ] random_flipped_halframes.mov [ 1.46 MiB | Viewed 594 times ]

[ Play Quicktime file ] random_delay.mov [ 857.4 KiB | Viewed 594 times ]

[ Play Quicktime file ] normal_state.mov [ 469.82 KiB | Viewed 594 times ]

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Re: Blackmagic io questions

Postby jmt4zj » Wed Jul 10, 2019 12:40 pm

Hi there,

I'm working with a setup with 2-4 inputs and 16-22 outputs in a single computer depending on the event configuration. I can only speak for question 1, but there was a HUGE difference in between blackmagic (decklink quad and duo) and AJA (Corvid 88) cards for the inputs. The outputs on the blackmagic aren't too bad (1-2 frames) but for the inputs my numbers for the blackmagic came close to yours at a whopping 8 frames of input latency. I haven't done a detailed latency analysis yet, but after installing an AJA card for the inputs I would estimate the input is at 1 frame latency - extremely fast. Also, I've had problems with certain very high end projectors (20,000 lumens) not liking native sdi signal from blackmagic outputs, but AJA cards work beautifully. In one case, this seemed like insufficient power for the length of sdi, but in a different scenario, it seemed like something with the signal itself.

In my opinion, there are big enough discrepancies that there should be some serious warnings on the wiki about which brand to buy. I would love to see more detailed data from more real life scenarios though!
Jonathan Thompson
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