Qlab and Black Magic Ultrastudio 4k questions

[Anhtu Vu]

I'm testing out a new cylinder Mac Pro with the Ultrastudio 4k for a big upcoming show where video quality is priority.

1-We noticed that playing the same video (prores HQ, 24p, 1920x1080) in Qlab does not look as nice as playing it via any professional video apps (Avid, FCP, Première) or even the simple and free apps that comes with Black Magic using exactly the same setting (1080p @24) on the card. Any suggestions ?

2- Is there a way to create different setting output using the same surface ? Let me explain.... we want to playback a  playlist containing several  videos cues with different frame rate. Each video will access the same surface, the Ultrastudio 4k, but I want the frame rate of the card to reflect the video's original frame rate. Therefore I must create several Ultrastudio surface, each with a different frame rate.... unfortunately, it does not work... any work around ? Thx

[Chris Ashworth]

On October 30, 2014 at 12:16:05 AM, Anhtu Vu (mia.s...@gmail.com) wrote:

I'm testing out a new cylinder Mac Pro with the Ultrastudio 4k for a big upcoming show where video quality is priority.

1-We noticed that playing the same video (prores HQ, 24p, 1920x1080) in Qlab does not look as nice as playing it via any professional video apps (Avid, FCP, Première) or even the simple and free apps that comes with Black Magic using exactly the same setting (1080p @24) on the card. Any suggestions ?

Can you provide a quantified version (i.e. recording of the output) of what “does not look as nice” means?

If not quantified, can you describe in words what’s wrong? Resolution? Frame rate? Color profile? Other?

2- Is there a way to create different setting output using the same surface ? Let me explain.... we want to playback a  playlist containing several  videos cues with different frame rate. Each video will access the same surface, the Ultrastudio 4k, but I want the frame rate of the card to reflect the video's original frame rate. Therefore I must create several Ultrastudio surface, each with a different frame rate.... unfortunately, it does not work... any work around ? Thx

QLab does nothing to set frame rates of external video devices. The CoreVideo thread that runs for each attached screen will run at a framerate, and QLab follows that. Whatever rate a given screen is running is the rate that QLab will update that screen, on whatever surfaces it appears. The concept of “surfaces" is unrelated to the frame rate of the devices used in the surfaces.

Best,

Chris

[Anhtu Vu]

Can you provide a quantified version (i.e. recording of the output) of what “does not look as nice” means?

If not quantified, can you describe in words what’s wrong? Resolution? Frame rate? Color profile? Other?

I'm testing using material that i know very well. It's basically an animation video....when i play it via Avid, Premiere, FCP and even Smoke. The animation looked exactly the same on all softwares...as expected. But when playing via Qlab, the outside edge of the of the animation subjects looked slight jagged as oppose to smooth compare to the above apps.

Aside from the playback software tested, all the harwarde and settings were EXACTLY the same:

Mac Pro Cylinder, Black Magic Ultrastudio 4 K with the card set at HD 1080p 24 - 1920x1080 in all applications including Qlab (see attachment). 

I'm using this professional broadcast monitor via SDI:

http://www.bhphotovideo.com/c/product/758921-REG/Sony_BVM_E250_BVM_E250_Trimaster_EL_OLED.html

There is also a slight gamma shift when playback videos within Qlab. 

QLab does nothing to set frame rates of external video devices. The CoreVideo thread that runs for each attached screen will run at a framerate, and QLab follows that. Whatever rate a given screen is running is the rate that QLab will update that screen, on whatever surfaces it appears. The concept of “surfaces" is unrelated to the frame rate of the devices used in the surfaces.

I'm not too sure what you mean here...again please reference to the attachment....when using the Ultrastudio with Qlab, one must set within Qlab the resolution and frame rate. Now for example, if my video cue in Qlab is referencing to a native 59.94i clip and i set  the Ultrastudio 4K in Qlab to HD 1080p 24, who is doing the pull up ? 

--
--
Change your preferences or unsubscribe here:
http://groups.google.com/group/qlab
 
Follow Figure 53 on Twitter: http://twitter.com/Figure53

---
You received this message because you are subscribed to a topic in the Google Groups "QLab" group.
To unsubscribe from this topic, visit https://groups.google.com/d/topic/qlab/l0DQLpoZR_g/unsubscribe.
To unsubscribe from this group and all its topics, send an email to qlab+uns...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[Sean Dougall]

On Oct 30, 2014, at 7:07 PM, Anhtu Vu <mia.s...@gmail.com> wrote:

the outside edge of the of the animation subjects looked slight jagged as oppose to smooth compare to the above apps.

Thanks, that’s helpful detail to have. We’ll see if we can recreate anything like this. Just to check, you don’t have any corner pins adjusted, right?

There is also a slight gamma shift when playback videos within Qlab. 

That’s difficult to explain, since QLab is simply passing pixel data to the Blackmagic device. I’m curious if anybody else on the list has encountered a similar issue.

Now for example, if my video cue in Qlab is referencing to a native 59.94i clip and i set  the Ultrastudio 4K in Qlab to HD 1080p 24, who is doing the pull up ? 

Live playback is fundamentally a different process from editing. Pull-up and pull-down are editing-specific terms, and describe frame-to-frame processes that don’t exist in the world QLab inhabits.

When you play media in an NLE like Avid, FCP, etc., it buffers a number of frames (usually a second or so, I believe) on the Blackmagic device, and allows the Blackmagic to drive both the framerate of the outgoing signal and the framerate of the media playback. Since the device is only ever outputting one single, pre-rendered, linear piece of media at a time, that allows it to guarantee a one-to-one correspondence between a media frame and an output signal frame. In that situation, the software could pull the media up or down 0.1% to match the outgoing framerate if necessary by simply telling the Blackmagic hardware to use a 0.1% faster or slower framerate. 

In a theatrical setting, a latency of one full second would be disastrous, as would a timing drift of 0.1%, so QLab cannot simply follow that one-to-one correspondence. QLab also has to assume that multiple media sources may be running at once on the same display, possibly with a mix of different framerates, and that they may have rate adjustments. Plus they may have audio tracks going to a separate interface, to which the video needs to stay synced. And multiple Blackmagic devices can also be assigned to the same surface, but they have no way to genlock to each other or clock to audio hardware (as far as I’m aware), so QLab can’t use two devices simultaneously to clock playback.

Instead QLab follows the computer's internal clock (or the audio clock, if there’s an audio track in the file in question), renders out the video at its native speed according to that clock, and sends each device the current frame each time a frame is needed. Since it’s not buffering any video as preroll, it’s using a completely different part of the Blackmagic code than an NLE would, which may account in part for the discrepancy.

But no matter what framerate the output signal is at, that’s not physically driving the refresh rate of the monitor, which will typically have a much higher native refresh rate. That’s what Chris was getting at; the result is that, as long as the framerate you’re outputting isn’t slower than the media framerate (which would result in dropped frames), all that changing around of formats isn’t necessary in order to match the media files, and won’t fundamentally change what happens at the monitor’s end.

Hope that helps clarify!

Best,  

Sean

[Christopher Ashworth]

(mobile)

> On Oct 30, 2014, at 11:49 PM, Sean Dougall <se...@figure53.com> wrote:
>
> That’s what Chris was getting at

(Although I did a bad job of being clear about that popup for the blackmagic device. Thanks for the better explanation Sean )

[Ron Peer]

Another semi related Blackmagic hardware question:
I'm using three Blackmagic minirecorders and studio 4k on a Mac pro connected throughout thunderbot to 3xPCI board.
System works great in any resolution, frame rate, surfaces, you name it!
I'm trying to setup a preview windows on the operator screen for those three sdi/hdmi inputs that would work simultaneously with qlab camera cues running on projectors.
I've tryied using Quartz composer, ScopeBox and even CamTwist combination.
Results are every time I'm trying to address same input simultaneously from qlab and another app, one of them halts.
Can you think of a workaround or this is a hardware limit I will have to learn live with?

[Dave "luckydave" Memory]

This is a limitation for Blackmagic devices. Only one application at a time can use them. You could create a Syphon surface for each camera, and use Simple Client, or another Syphon-enabled application to create the preview windows.

-- 

luck...@figure53.com 

[Sean Dougall]

Quick update on this issue:

the outside edge of the of the animation subjects looked slight jagged as oppose to smooth compare to the above apps.

This turns out to be easy to reproduce—it’s an issue with interlaced display modes. It appears that the Blackmagic device is extracting the even field of each frame and sending it twice, skipping the odd field and effectively halving the vertical resolution. I have a support request in with Blackmagic to see if this is a bug on their end, or a step I’m missing in QLab’s code. I can verify that full frames are being sent out at the full frame rate (e.g. 1920x1080 every 1/29.97 second for the 1080i 59.94 mode), but the conversion from a full frame of pixels to a pair of interlaced fields is happening incorrectly.

In the meantime, if your gear supports progressive modes, those are outputting correctly.

--

Sean Dougall

se...@figure53.com

[Sean Dougall]

At long last, we have a culprit. Launch System Preferences, select the Blackmagic Design pane, and uncheck the checkbox that says “Remove field jitter when video is paused”.

That seems counterintuitive at first, since QLab’s video output is not actually paused, but it makes sense as a result of the fact that we’re doing synchronous (frame-by-frame) output instead of buffered output. For the vast majority of applications, playback means buffered output and paused video means synchronous output. QLab is the odd one out in that way, so the terminology doesn’t quite fit.

Blackmagic provides a method for unchecking that option programmatically, so we should be able to make QLab use the correct setting automatically. For now, unchecking it manually will restore your output to include both fields.

—

Sean Dougall

se...@figure53.com

[Greg Leeper]

Does anyone know if this has been fixed 'programmatically' or do we still need to go into BM prefs and check the box?