April | 2016 | brainwagon

I was trying to figure out how to screencast to twitch.tv using ffmpeg. A couple of hours of tinkering resulted in the following command line which does a bunch of stuff.

It captures the X desktop at 15 fps and 1920×1080 resolution.
It grabs frames from my webcam (a Logitech Pro 9000) at 320×240 resolution.
It then combines the two into a 1024×576 image, with the video overlayed at the top right and a banner at the bottom that displays a couple of lines of text.
It then ships it to the twitch.tv server. If you grab this code, you need to add your own streaming URL for your own channel.

[sourcecode lang=”bash”]
#!/bin/bash

/home/markv/bin/ffmpeg \
-y -thread_queue_size 64 -f x11grab -s 1920×1080 -framerate 15 -i :0.0+0,0 \
-thread_queue_size 64 -f v4l2 -input_format mjpeg -framerate 5 -video_size 320×240 -i /dev/video0 \
-filter_complex \
"[0:v] scale=1024:576, setpts=PTS-STARTPTS [bg]; \
[1:v] setpts=PTS-STARTPTS [fg]; \
color=0x336699cc:1024×64, drawtext=textfile=twitch.txt:fontfile=/usr/share/fonts/truetype/dejavu/DejaVuSansMono-Bold.ttf:x=10:y=16:fontsize=16:fontcolor=white [bottom] ; \
[bg][fg] overlay=W-w-16:16 [out2]; \
[out2][bottom] overlay=0:H-64, format=yuv420p [out]" \
-map "[out]" \
-vsync 1 \
-c:v libx264 -b:v 500k -maxrate 500k -bufsize 1000k -framerate 15 -g 30 -crf 30 -preset fast -pix_fmt yuv420p -tune zerolatency \
-f flv rtmp://live.twitch.tv/app/live_XXXXXXXX_XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
[/sourcecode]

A few additional notes:

The default DNS server for my ISP don’t serve DNS requests for the live.twitch.tv server. I fixed this by adding the Google DNS servers to my router (8.8.8.8 and 8.8.4.4).
The script appears to work pretty well, but sometimes has difficulty starting up. And, when the script crashes, the remote clients don’t time out for a considerable time.
I haven’t tested this extensively.

Buyer beware, but I hope it is useful.

Most of my hacking occurs in a vacuum: where I sit in my living room or in my home office and toil away silently on projects which occasionally get documented here, but which all too often are just my way of passing the time. On the way to work, I was asking myself what I could do to boost my own excitement about these projects, and provide some incentive to do more, and on a more regular basis.

So, I had an idea which is almost certainly not new: the idea of a virtual hackerspace.

For years, I used to donate my Friday evenings to the Chabot Amateur Telescope Makers workshop. I’d go down and spend three or four hours showing up, seeing who needed help on a telescope project, or I’d bring my own and work on that. I want to create a more generic “workshop network”, where people can meet regularly for a kind of hackerspace parallel play using video conferencing technology.

In some sense, it’s just an extension of Google Hangouts. The idea would be that each participant would have a webcam/microphone setup, and at the appointed time, we could all just open our cameras and mics, say “hi” to one another and then go about our business, potentially sharing our projects or asking questions of the group at large. I’ve mostly used Hangouts for simple one-to-one conversations, and have little experience with larger groups, and didn’t really find any obvious links about how to manage larger groups. Does anyone have any recommendations on how to setup such a network? I am not really interested in creating a “show”, but really more of a set of spaces which encourage mutual collaboration and interest.

I’m willing to entertain other technologies as well, if people have better suggestions.

And, if you would be interested in joining in this kind of “network”, drop me a note here or on twitter (@brainwagon). I’ll try to do an update of what I learn.