3D postcards

Posted in Games

If you wink with alternate eyes ten times a second and stare into the distance, you can pretend you have a Rift!

Proteus Rift jitter gif

This was hand rolled, but we should be able to modify the postcard system to produce stereoscopic pairs to drop straight into an animated gif creation tool for 3d postcards!


Implementing HTTP Live Streaming using a Dropcam

Posted in General, Mobile

I’m posting this up as a helpful reference guide for anyone who is looking to implement HTTP Live Streaming using a Dropcam. This technique opens up Dropcam live streams to people on iOS devices without them being required to download and install a separate application.

Last week we got a WiFi-capable webcam from dropcam.com delivered to the office, as we wanted to have a method of people interacting with a Little Printer via the HTTP API, and for them to be able to see the results on the hardware itself.

As a fun interaction system this worked very well, and we’ve had a lot of people send us notes, but I was a little frustrated because Dropcam require you to download an app if you want to view it on mobile iOS devices. Apple’s HTTP Live Streaming protocol has been around for a while now, and still represents one of the more sane methods to standardise live streaming on the web (along with MPEG-DASH). Wouldn’t it be good if we could somehow construct a media pipeline to convert the raw Dropcam RTMP stream into a live stream, I thought.

The first step was to find details of the stream that the Flash player interacts with, and luckily this is already solved by the Dropcam Ruby gem. Firing this up in irb allows us to find exactly what we need.

dropcam = Dropcam::Dropcam.new("YOUR_USERNAME", "YOUR_PASSWORD")
camera = dropcam.cameras.first
puts camera.stream.rtmp_details

{:app=>"nexus", :host=>"stream.dropcam.com", :playpath=>"93475eb827f8ac7392a3c83a99241c433", :variables=>{"S:"=>"2747ca2b38f93475eb8277392a3ac4941339c832f8ac"}}

Looking at the information we get back we now we have an application name, a host, a path and some sort of session token. Having found this information it’s worth checking if the stream credentials are valid by piping the output of rtmpdump into VLC.

$ rtmpdump --live --app nexus --host stream.dropcam.com --playpath 93475eb827f8ac7392a3c83a99241c433 --conn S:2747ca2b38f93475eb827f8ac7392a3c83a99241c4 | /Applications/VLC.app/Contents/MacOS/VLC

Once the information gives us a valid RTMP stream from Dropcam’s servers, we can move onto constructing a ffmpeg invocation which will open the RTMP stream, transcode to h.264 and output video in HTTP live streaming format. After some research on the ffmpeg mailing list, the resulting command line is:

ffmpeg -rtmp_app nexus -rtmp_conn S:2747ca2b38f93475eb827f8ac7392a3c83a99241c433 -rtmp_playpath 93475eb827f8ac7392a3c83a99241c4 -i rtmp://stream.dropcam.com/ -s 400x224 -c:v libx264 -b:v 300000 -vprofile baseline -preset medium -x264opts level=41 -hls_time 3 -hls_list_size 10 -hls_wrap 30 -start_number 1 stream.m3u8

This opens the RTMP stream, re-encodes the video as a 300 x 224px h.264 stream at a data rate of 300k and automatically creates a filed called stream.m3u8 which will continually be updated by the streaming process to point to the most recent video files.

The last step is to create a master m3u8 playlist file and an HTML page which will implement the video tag to point at the master playlist. They look like:




HTTP Live Streaming Example


If you ensure that the directory you’re creating the video files in is served over HTTP, then if you browse to the index.html file on your iOS device you should be able to hit the play button and start watching, app free.

There’s more detail to be found on HLS in ffmpeg from this thread on the ffmpeg mailing list http://ffmpeg.org/pipermail/ffmpeg-user/2013-May/014932.html.