more than 4 video inputs? (redux)

[thatmattrogers]

I know that this has come up before but it it was a VERY old thread so I thought I'd just start again.

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Isadora has a hard limit on video inputs. so I can only capture streams from 4 cameras at a time.

that seems fine. I don't have unlimited USB ports and things tend to go wrong whenever I've tried using a hub for video.

the only way I can see to extend that number is to have one of the inputs actually be an output from a second computer running another instance of Isadora which in turn has 4 cameras being input into it.

in my head that second computer has a simple patch which allows me to select any of the video streams that I want using a simple osc command. it would introduce a little bit of extra lag but it's definitely workable.

the only problem I see is if I want to use all 7 camera feeds at the same time meaning it might end up being a bit of a headache.

is there a more streamlined way to go about this... or is this basically THE WAY to work with lots of cameras?

[Juriaan]

@thatmattrogers

Hi there!

It depends a lot on your OS. You are right that Isadora right now can only handle 4 Live inputs at the same time. This is basically because back in the day when we released this feature computers were not as powerful as they are now. 16Gb of RAM for example was something that was not as common.

Anyhow, it will take a while before we lift this. If you could share some details we might be able to give you a temporary workaround that doesn't require a second machine.

Let us know :)

[thatmattrogers]

@juriaan

Hi,

on this project the main production machine runs windows. It's not the most powerful machine you'll ever come across; its got 16gb of Ram and is running an AMD 5900HX 8core APU.

The tricky thing about this one is that its a research project playing with live video production and simultaneous live performance and streaming; so as I'm building the initial setup I'm trying to work in as much flexibility as I can in terms of available camera angles, there's also been a suggestion of using a kinect so that's a hole other video feed as well.

In terms of available USB ports; I've got 6 without having 2 video inputs sharing the same bus, so the limits would be 5 capture cards and a kinect.

of course things get a little easier if we don't end up needing to use a feed from every single camera at once, because i can just use a usb video switcher like an ATEM mini or something; but at this stage, like I said, it's all about creating maximum flexibility so there's as little friction between ideas and the tech as possible.

[Fred]

@thatmattrogers You have some options, if you are using HD inputs you can use a 4k capture device and a 4k quad splitter (watchout for latency it varies betwen devices) with 4 HD inputs. You then need to crop each input to treat them individually. You can also use another computer and send the signal via NDI over the network. Or you can capture internally and use something like blacksyphon (there is a spout eqiuvalent) to send extra video streams to Isadora. 

Just a note, live video capture is a computationally expensive task, difference capture systems have different overheads, some cheap USB capture cards have a higher overhead as they send compresed streams that need to be decompressed (generally on the CPU) before they can be used. Blackmagic and other higher end capture cards often have less overhead, but either way 7 live inputs is a heavy task just to get the data from the capture device and on the GPU where Isadora can do something with it.

[thatmattrogers]

@fred I'm a complete novice at this so bare with me.

I've never used NDI so I'm coming in a bit blind, but from a cursory reading it could easily handle 4 video streams over a network. which seems great.

the thing I can't quite get my head around is 2 things:

1: how does isadora interface with NDI, is it though a video in type watcher? I don't know.

2: would it be possible to pre process the video into a friendlier codec on one machine before sending it to a second in order to reduce the overhead on the production machine? obviously that would increase lag... but it is it even theoretically possible?

[Fred]

@thatmattrogers 

1.There is an NDI watcher, again this is CPU decoded so there is a reasonable overhead.

2. Generally no, the overhead comes from the capture process, what capture card are you using?  If you were using some cheap capture dongle that sends a compressed H264 stream you ***may get less overhead on one machine by sending NDI from a second, but at that point it would be a far from optimal setup and getting a proper capture device would be advisable. There are blackmagic cards that have 4 adn 8 inputs, AJA cards that have similar, Bluefish cards that also have multiple inputs.

To do 7 HD inputs I would be looking at a threadripper machine and a beefy GPU like the 3080.