Screencasting on Linux

I've been wanting to do screencasts on Linux for some time now, and my big stumbling block has been determining what tools to use.

The tl;dr:

  • Use recordMyDesktop to record video clips, but afterwards, re-encode them to AVI (see the script I used)
  • Record audio to WAV, or convert compressed audio to WAV format afterwards.
  • Use OpenShot to stitch clips together and layer audio and video tracks.
  • Remember to reset the video length if you change the playback rate.
  • Export to a Web + Vimeo profile for best results.

Stumbling Blocks

recordMyDesktop is a fairly simple tool, and allows you to record actions you're taking, and simultaneously capture audio. However, it creates an ".ogv" (Ogg Vorbis video file) -- which is basically useless for anybody not on Linux or FreeBSD. Additionally, I often like to record in segments; this makes it less likely that I'll make mistakes, and, if I do, I only need to record a small segment again, not the entire thing. recordMyDesktop is only for creating screencasts, not merging them.

So, recordMyDesktop went into my toolbox for the purpose of recording the video portion of my screencasts.

Which brings me to the next point: I also prefer to record the audio separately from the screencast portion itself; this way I don't get typing sounds in the recording, and I'm less likely to lose my train of thought as I'm speaking. To this end, I ended up using quite simply the "Sound Recorder" utility (gnome-sound-recorder). It's not great, but with a reasonable microphone, it gets the job done. I chose to record the audio as MP3 files.

However, this means that I now have video and audio tracks. So my toolbox needed a utility for overlaying tracks and laying them out on a timeline independently.

I looked at a few different free tools for Linux, including Avidemux, Cinelerra, and PiTiVi. Avidemux was not featurful enough, Cinelerra was too difficult to learn (it's more of an advanced user's tool), and PiTiVi kept crashing on me. So, I used the lazyweb, and tweeted a question asking what others were using -- and the unanimous response was OpenShot (http://www.openshotvideo.com/).

OpenShot hit the sweet spot for me -- it was easy to pick up, and didn't crash. However, I discovered problems when I exported my project to a video file. My video, regardless of whether or not I changed the playback rate, always played at about 2X normal speed. The audio always truncated 1 to 2 seconds before completion.

In doing some research, I discovered:

  • There are known issues with Ogg Vorbis video files. Evidently, the compression creates issues when re-encoding the video to another format.
  • Similarly, compressed audio can lead to issues such as truncation.

Since recordMyDesktop doesn't allow you to select an alternate video codec, I had to use mencoder to transcode it to another format. I chose AVI (Audio Video Interleave, a video container format developed by Microsoft), as I knew it had widespread support, using an mpeg4 codec (also widely supported). I used the following script, found at http://askubuntu.com/questions/17309/video-converter-ogv-to-avi-or-another-more-common-format, in order to encode my files:


for f in *.ogv;do
newFile=${f%.*}
mencoder "$f" -o "$newFile.avi" -oac mp3lame -lameopts fast:preset=standard -ovc lavc -lavcopts vcodec=mpeg4:vbitrate=4000
done

That solved the video issue, but I still had to solve the audio issues. I quickly re-recorded one audio segment in Sound Recorder, and told it to use the "Voice,Lossless (.wav type)". When I used this version of the audio, I had no issues, other than the audio length being mis-reported within OpenShot. Instead of re-recording all segments, I installed the "Sound Converter" utility (`sudo aptitude isntall soundconverter`), and used that to convert all my MP3 files to WAV. Interestingly, OpenShot reported the audio lengths correctly this time; go figure.

Once that was done, I was able to start stitching everything together. A few notes, in the hopes others learn from my mistakes:

  • Several times, I wanted my video to playback slower. This is very easy to do: right click on the clip, select "Properties", and select the "Speed" tab, and adjust as necessary. However, that's not all you need to do; you need to also re-adjust the length of the clip. Simply take the existing length, and divide it by the rate of play. As an example, if the length is 44 seconds, and you specify a 1/2 rate (0.5), you'd do 44 / 0.5 = 88, and set the length of the clip to 88s.
  • If you find that OpenShot is reporting your audio clip lengths incorrectly, use another tool to find the accurate length, and then set the length to that. I typically rounded up to the next second, as most tools were giving the floor value from rounding.
  • I chose to export using the Web + Vimeo HD profile. This worked perfectly for me. It created an mpeg4 file that I could preview in a browser, and then upload without issues. Your mileage may vary.

Hopefully, this will serve as a reasonable guide for others foraying into screencasts on Linux!

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