Wednesday, February 27, 2008

Success with gstreamer

A few weeks ago I nearly threw my laptop down the hallway at work out of frustration with Kino and Pitivi. All I wished to do was create a simple screencast using open source software. I later tried some tips I found on the Fedora Screencasting wiki only to find the recommended splice script out of date.

Though the script was broken on F8 it did give me insight into the power of the gstreamer framework. I knew that whenever I had the time I should dig in a little deeper. With the help of this Linux Conf Austrailia talk I was able to figure out what needed to be changed in order to get the splice script working again on F8.

Here's how I spliced my theora video (made with istanbul) with a wav file recorded in audacity:
gst-launch oggmux name=mux ! filesink location=ldap-gst.ogg { filesrc location=ldap.ogg ! decodebin name=v } { filesrc location=ldap-audio.wav ! decodebin name=a } { v. ! queue ! ffmpegcolorspace ! theoraenc ! queue ! mux. } { a. ! queue ! audioconvert ! vorbisenc ! queue ! mux. }

As a big fan of golfing on the command line I can appreciate convoluted oneliners. The big trick to getting the script running was:
  1. Remove the version number from the 'gst-launch' executable (why hard-code that anyway?)
  2. Corrected syntax (honestly, I mostly cargo-culted this from examples I found on the interweb)
  3. Changed 'rawvorbisenc' to plain old 'vorbisenc'. The talk mentioned 'gst-inspect' which for me was the key to finding out what my system could do.
Now what I would like to do is update the Fedora wiki. Sadly, I can't figure out how to edit It appears to be an 'Immutable Page'. How should this get updated? Do I email the mailling list? There's probably a doc explaining this on the wiki somewhere so I'll just have to dig for it sometime (unless some knowledgeable reader can enlighten me).


Jef Spaleta said...

Okay so the original splice script on that wiki page was totally my fault. I put that page together when I first got istanbul into the repository. I sort of assumed that it being a wiki, people would come behind me and keep it updated.

I don't know why the wiki page is immutable now. if I get a chance I'll take a look at it.

If you want you can send me the updated script and I'll get it in the wiki.


Till Maas said...

I can edit the wiki page, maybe you need to follow this procedure:

brenton said...

Thanks for the help! I read through the info on gaining access to the edit the Fedora wiki. I'll have to go through those steps this weekend.

Jef, in the meantime I'm emailing you the updated script. Thanks for the original script since that was what pointed me in the right direction.


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