Web Presenter and OBS Studio

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darin_allen_newberry

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Web Presenter and OBS Studio

PostMon Sep 04, 2017 11:32 pm

AUDIO AND VIDEO OUT OF SYNC: I use the Windows version of OBS Studio [version 20.0.1] with a Blackmagic Design Web Presenter with current firmware version, and do not stream with it but record its output to a Solid State Drive for editing. I use OBS's x264 encoder to create a QuickTime.Mov file, using a PC with 12 GB of RAM and a GeForce 940MX GPU. OBS says the CPU load is about 35% with the settings I now use. I run just a few other processes in the background while recording, but nothing that is also trying to use the SSD.

I know the Web Presenter will vary its framerate, which often moves between 27.97 fps and 29.97 fps, but am very frustrated because in many places in the created .MOV file, I find the audio and video out of sync, where it seems either the video or audio get ahead of one another, and I have to do a lot of editing of the audio to salvage the recording.

I don't know whether OBS or the Web Presenter is at fault, or if hardware and software settings are incorrect. Should I be using Constant Bit Rate, instead of Variable Bit Rate? I intend to soon use a pair of BMD Intensity Shuttle to ensure I always get 29.97 fps, but until that time, I need to have rock-solid sync between the video and audio being created.
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Tim Douglas

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Re: Web Presenter and OBS Studio

PostWed Sep 06, 2017 7:30 am

The 1.2 update solved it for me but if you're already on the latest firmware I'm not sure what could cause this. Just to cross it off completely I would downgrade to 1.1 and upgrade back to 1.2.

OBS also has audio delay settings, if you or someone else has been playing with various settings they maybe a delay was added at some point and not removed.

Hope this helps.
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darin_allen_newberry

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Re: Web Presenter and OBS Studio

PostThu Sep 07, 2017 7:00 pm

I just realized there is a ratio involved in the audio track editing I am doing, to keep it in sync with the video. Approximately every nine to ten seconds of audio--quiet spaces permitting--I have to make a cut and push the unplayed audio over to the right, six to nine frames. I take a spare audio segment of the approximate needed length, and shift it right, using it as a rough guide for where to make the next razor cut. OBS Studio records audio & video from the Web Presenter anywhere from 23 to 29 frames per second, regardless of what framerate I have set the software to. This is vexing, as well.
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Tim Douglas

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Re: Web Presenter and OBS Studio

PostFri Sep 08, 2017 9:32 am

That audio issue is weird. Looking back at your first post, the CPU usage seems high, especially for the specs you've got. I use a mid 2012 MBP (8GB RAM, dual core i7, integrated graphics, I'm not experiencing these issues (but I also don't record very often).
I have a possible diagnosis.

The WP heavily compresses the video but OBS isn't expecting this and will de-compress then re-compress this source, all on the fly, by default (as far as I can tell). So you may be having issues related to that. I think it's a pretty common issue when integrating the WP into a workflow, but usually it just results in dropped frames, I'm not familiar with this audio issue.

Depending on your settings you might also be encoding the video again for the .MOV file. (That's potentially 2 unnecessary times in OBS)

If this is the cause you will be getting: high CPU usage, choppy video or a different framerate than what the WP reports (it should be identical).




You have a few options to fix this:

1.
You could probably fix this by changing your OBS settings.
You need to make sure OBS does almost no encoding. Here is a link to another thread with some details for that:https://forum.blackmagicdesign.com/viewtopic.php?f=4&t=63743#p361438

You also need to match the streaming and save file settings so OBS doesn't encode the video twice. Maybe that doesn't apply if you don't actually hit stream.

2.
You could just record the WP input with another software. On a mac I've found the simplicity of Quicktime more reliable in a pinch rather than fiddling with OBS settings.

3.
However, since you aren't streaming and presumably want a higher quality file to edit, you should probably get the WP's compression out of the way altogether. That should also resolve this or any other weird issues.

You could add an UltraStudio HD Mini to the SDI PGM out from the WP and record to the format you want without the PC.

4.
You can go from the SDI PGM out of the WP to the PC with an Ultrastudio Mini Recorder, intensity Shuttle or a DeckLink card. This gives you higher quality source which you could record with a Quicktime equivalent on the PC.

5.
You could replace the WP with a couple of Decklink cards and switch inside of OBS without the WP. Again, you need to adjust the settings to only encode the footage once. But using OBS at all adds too many variables and other issues could pop up.

Apologies if this isn't clear. Hope it helps.
Give an update, I'd like to know how it works out.
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darin_allen_newberry

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Re: Web Presenter and OBS Studio

PostFri Sep 08, 2017 5:59 pm

Tim, thanks for your thoughtful response to my situation. The interplay between the WP encoder and OBS Studio that you describe, seems a good explanation. I am thinking of getting OBS Studio off the job, and using BMD Intensity Shuttle cards to iso each camera with, and hope my laptop has enough horsepower to do this. It has an i7 7500U 2.7 GHz CPU with 12 GB RAM and an NVidia GEForce 940MX 2GB GPU, with several USB 3.0 ports, a USB-C port, and an SSD. Would multiple copies of Media Express run?
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Tim Douglas

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Re: Web Presenter and OBS Studio

PostSat Sep 09, 2017 5:14 pm

This sounds like an interesting experiment. I have no experience with Media Express so I can only guess how this would work out.

You can raise/lower the compression to suit, but disk space might be an issue with just the SSD (or speed with an external drive). But I'm not sure you can run multiple instances of Media Express at all.

I might have misunderstood what you're trying to do though. It seems like you're just going to record each camera independently, if that's the case why use the laptop at all? Is it possible to record in-camera and import the footage later?
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darin_allen_newberry

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Re: Web Presenter and OBS Studio

PostSun Sep 10, 2017 5:49 pm

In-camera recording is not desirable, because it is only HDV [4:2:0] and I would rather use the analog component output from each camera.

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