[Esug-list] To improve the quality of the ESUG videos

Steven Kelly stevek at metacase.com
Wed Nov 1 10:11:12 EDT 2017

NDI has Linux support; it’s just that they don’t make the prebuilt Tools download for it. The Linux SDK contains code for sending video, but not for screen capture.

Before I’ve just sent done Linux screen capture with ffmpeg’s x11grab:
ffmpeg -f x11grab -video_size cif -framerate 25 -i :0.0 /tmp/out.mpg

Rather than saving to a file, ffmpeg can also stream e.g. as an RTMP stream (that Livestream Studio, vMix and OBS can pick up):
E.g. from a Raspberry Pi’s camera, encoded in the Pi GPU to H.264 and sent by ffmpeg as a flv RTMP stream:
raspivid -n -vf -hf -t 0 -w 960 -h 540 -fps 25 -b 500000 -o - | ffmpeg -i - -vcodec copy -an -metadata title="Streaming from raspberry pi camera" -f flv $RTMP_URL/$STREAM_KEY

Looks like ffmpeg has now also implemented NDI: https://www.ffmpeg.org/ffmpeg-devices.html#libndi_005fnewtek-1
So presumably just merging the above commands to take the input from x11grab rather than piped from raspivid, and changing the output from flv to libndi_newtek $NDI_NAME would work on Linux.


From: David Mason [mailto:dmason at ryerson.ca]
Sent: Wednesday, November 1, 2017 2:05 PM
To: Steven Kelly
Cc: Stéphane Ducasse; ESUG Mailing list
Subject: Re: [Esug-list] To improve the quality of the ESUG videos

NDI looks cool, except no Linux support, and quite a few ESUG presenters use Linux, if I remember correctly.

On 31 October 2017 at 13:21, Steven Kelly <stevek at metacase.com<mailto:stevek at metacase.com>> wrote:
Hi Stef,

I’ve not used that particular capture card, but a few others certainly – from low end to high end, mostly for live streaming of cameras and PC screen. I use Livestream Producer and Livestream Studio for that, but they are more expensive that vMix and OBS Studio that I recommend below.

That AV.io HD is pretty high end, but has the possible problem that there’s no video output, so you couldn’t put it directly between the presenter’s PC and projector. You’d need splitters for whatever inputs you might have from the PCs. One option may be if the projector has an output, generally VGA, and you could get the signal to capture from there, always in the same format regardless of the presenter’s PC. I haven’t tried that enough to know how much quality etc. varies.

How are you recording currently, and with what products?

-          webcam?

-          An SD card in the camera?

-          A video cable from the camera to a video capture card on a PC?

-          Some computer video format sent by the camera to the PC via USB/IP?

If you want to improve the videos, I’d suggest:

-          using the camera to film the speaker rather than the slides. The current camera is really suffering trying to record the screen, but contrast improves quite a bit when it occasionally films the speaker, e.g. here<https://youtu.be/lBxwaUvortA?t=8m26s>.

-          using a capture card as suggested to grab the projector input.

-          using something like vMix<https://www.vmix.com/purchase/> or OBS Studio<https://obsproject.com/> on a separate PC to take the audio and video inputs and mix them into a stream, which could go live to YouTube. (Not so much because I think ESUG should be live, but because it’s less time consuming to do the video mixing live at the conference, rather than having to mix and upload everything in the evening or after the conference.)
An alternative approach: The cool way to do this these days is to use NDI<https://www.newtek.com/ndi> – a fast video codec, that in this case could capture the screen on the presenter’s PC (NDI Scan Converter<https://www.newtek.com/ndi/tools/>, simple install) and be picked up over the (preferably wired) network by the PC used to record the camera. Cost: $0, and no fiddling about with extra video cables. The downside is of course the install. Mind you, if you had the video PC connected to the projector, showing the presenter’s video output as it is received via NDI, that means you avoid the normal problems of trying to get each PC working with the projector.

All the best,

From: Esug-list [mailto:esug-list-bounces at lists.esug.org<mailto:esug-list-bounces at lists.esug.org>] On Behalf Of Stéphane Ducasse
Sent: Tuesday, October 31, 2017 5:02 PM
To: ESUG Mailing list
Subject: [Esug-list] To improve the quality of the ESUG videos

Hello Smalltalk Friends

We would like to improve the capture of screen for the

I googled a bit after talking with peter uhnak and we could capture the screen output (on the way to the


I would like to know if one of you got experience with such devices.


Stéphane Ducasse
http://www.synectique.eu / http://www.pharo.org
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S. Ducasse - Inria
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