How to create a WebM video file?

I set this up recently, but it's kind of a pain. Here's what I had to do:

First, build ffmpeg from source to include the libvpx drivers (even if your using a version that has it, you need the newest ones (as of this month) to stream webm because they just did add the functionality to include global headers). I did this on an Ubuntu server and desktop, and this guide showed me how - instructions for other OSes can be found here.

Once you've gotten the appropriate version of ffmpeg/ffserver you can set them up for streaming, in my case this was done as follows.

On the video capture device:

ffmpeg -f video4linux2 -standard ntsc -i /dev/video0 http://<server_ip>:8090/0.ffm

• The "-f video4linux2 -standard ntsc -i /dev/video0" portion of that may change depending on your input source (mine is for a video capture card).

Relevant ffserver.conf excerpt:

Port 8090
#BindAddress <server_ip>
MaxHTTPConnections 2000
MAXClients 100
MaxBandwidth 1000000
CustomLog /var/log/ffserver
NoDaemon

<Feed 0.ffm>
File /tmp/0.ffm
FileMaxSize 5M
ACL allow <feeder_ip>
</Feed>
<Feed 0_webm.ffm>
File /tmp/0_webm.ffm
FileMaxSize 5M
ACL allow localhost
</Feed>

<Stream 0.mpg>
Feed 0.ffm
Format mpeg1video
NoAudio
VideoFrameRate 25
VideoBitRate 256
VideoSize cif
VideoBufferSize 40
VideoGopSize 12
</Stream>
<Stream 0.webm>
Feed 0_webm.ffm
Format webm
NoAudio
VideoCodec libvpx
VideoSize 320x240
VideoFrameRate 24
AVOptionVideo flags +global_header
AVOptionVideo cpu-used 0
AVOptionVideo qmin 1
AVOptionVideo qmax 31
AVOptionVideo quality good
PreRoll 0
StartSendOnKey
VideoBitRate 500K
</Stream>

<Stream index.html>
Format status
ACL allow <client_low_ip> <clie