Screencast production: Lessons learned from the making of my first screencasting

1) Setup

Install software: You first have to setup your toolset (audacity, xvidcap, ffmpeg, avidemux).

Create screencasting environment: I didn't want the screencast to show all the peculiarities of my work environment (e.g., filesystem contents, virtualbox machines, browser bookmarks and extensions, etc.) so I started fresh by creating a new demo user just for that.

2) Rehearsal

This is where you walk through the various things you would like to show while thinking about what you want to communicate.

Tips:

• Try to logically segment the action into easily defined scenes
• Write an outline of the script

3) Shoot video

You shoot the video at the highest possible quality. Flash Video Screen is lossless but the captured frame rate is poor. MP4 at the highest quality settings has a slightly lower picture quality but the frame rate is much better.

You're not trying to get things perfect and with the correct timing because that's very difficult.

Instead you want to shoot in a way that allows you to redo bad parts and cut out mistakes later in editing without having to start over.

The trick is to remember the approximate mouse position at the beginning of a scene (e.g., middle of the screen) and if you want to start over just bring the mouse back to that location and redo it.

Pausing: Pause as much as you want if it helps you think things through. That can be easily edited out and it seems to work better then trying to rush through everything.

xvidcap complicates things with it's tendency to crash unpredictably.

To get around this every so often I make note of the mouse position, stop capture, and click on the next button to start recapture in a new file (e.g., take-0002.avi instead of take-0001). I then return the mouse to the original position and when I stitch the files together I will edit out the connecting tissue so it looks like one smooth seamless video.

4) Convert captured video to workprints

To edit the video in avidemux you'll want to use ffmpeg to convert the raw footage into a fast, lossless format with no key-frames such as FF HuffYuv (ffvhuff):

		ffmpeg -i path/to/file.avi -vcodec ffvhuff hugefile.avi

This allows you to edit with frame precision and save as many times as you want without loosing any video quality in the process.

The trade off is disk space, and at a 114Mbps bitrate (14MB/s) you'll need lots of it. 1 minute equals 860MB.

5) Edit the workprint

In a nutshell you use avidemux to:

1. stitch the pieces together to create the illusion of one seamless video.
2. cut out the bad parts / retakes but don't cut out pauses yet, they'll be useful during audio/video synchronization.

A big gotcha is that Avidemux doesn't provide an Undo and is easy to make serious mistakes in so you'll want to save frequently. Avidemux allows you to save your edits in a "project" file (basically a script that records your actions) but sometimes this doesn't seem to work very well so you will want to save your progress by actually saving your edits into a new video which will take a while but is still much faster with FFVHUFF than with other formats (e.g., especially in "Copy" mode).

6) Script "narration"

This is the part where you play back a section of the video, pause it and then write down notes on useful things you would want to say. Rinse, repeat. Then you translate your notes into a script that doesn't sound too contrived.

At the beginning you may want to introduce yourself and provide a short overview of what you are going to show, to prime the expectations of your viewers, motivate them to see the entire video and make it easier for them to follow you.

Of course, there are many ways to narrate a screencast. The natural tendency is to grunt your way through it while thinking out loud, but I think it's best to make the most of the audio channel to add:

• audio titles: a spoken summary of what you are doing or going to do. Of course, the user has eyes so you don't have to replicate the information, but it does help to set the context up and help him interpret what they are seeing.
• provide useful commentary and insights that you think would help users "get it".

7) Record narration

Naturally, you'll want to start with a sound test. Especially if you're using amateurish equipment.

For best results, don't try to do this while watching the video, and forget about timing issues altogether. Just focus on reading the narration script in a natural, friendly tone.

Tips:

• Don't start over: If you make a mistake, or don't like how something sounds don't worry about it, just pause and continue and redo it. It's easy to edit out the mis-steps later.

• Speak in a consistent tone and volume unless you want the listener to start noticing the characteristics of your voice, and usually you just want them processing what your saying without any distractions.

• Pause and breathe:

  This may sound trivial but if you forget to breathe your voice won't sound as good and you will eventually run out of breath.

  Also, audio is easier to edit when there are pauses between sections because you can identify that in the graph of the waveform.

• Try to do it in one take.

  Especially if you're using unprofessional equipment.

  I use headphones and every time I took them off and put them back on the positioning of the microphone was a bit different and my voice sounded different.

  Also at different times you'll likely be in a different mood and this too can effect how your voice sounds.

  BTW, I discovered this a bit late and so I think it's possible to make out the different sections in the video.

8) Video/audio syncing

How long it takes: doing this right is a significant amount of work. Once you get the hang of it, expect this to take 20-30 minutes per minute of synchronized video.

Order: you start at the beginning of the audio/video, and work your way gradually through the soundtrack and video track until you reach the end. Doing it in a different order can screw up your synchronization and you'll have to redo it or at least check that it still works.

Editing primitives: I managed to do all of my synchronization done using only two basic primitives - removing and inserting pauses in the audio and video, in a way that synchronizes key audio landmarks (e.g., the start and end of an audio section or an important part in the middle) to what is happening at same time in the video.

In both Avidemux and Audacity this is easily accomplished, though it is somewhat easier in Audacity because the timeline of audio is a bit easier to visualize (I.e., you can see where a section begins and ends without having to play through it).

Most of the time I just took count of the common timeline counters (e.g., number of seconds since video/audio began) to do this but if you want to actually see and hear the result in progress you can export the soundtrack into wav (takes a couple of seconds) and then tell avidemux to load the track from an external file.

I didn't do that very often though and in some cases it shows but usually I didn't need to.

9) Audio cleanup

Played with a lot of options (including the Audacity CleanSpeech chain). Noticed that heavy processing tends to diminish the quality of the speech so that some parts can become difficult to understand.

In the end, I cleaned up the sound using only two basic Audacity filters:

1. Noise removal
2. Amplification

10) Encoding

Use Avidemux to encode as configuring of all the codec options is much easier. By contrast with ffmpeg I always got very high bitrates at a lower quality.

Encoded the master video in lossless FFV1 and WAV codecs. That comes out to 1GB (4:1 compression ratio).

Encoded the published video in H264 and MP3. Note that you will pay for narrower bitrates with a longer encoding time.

H264 configuration options:

• motion estimation

  • partition decision - 6B (very high)
  • method - uneven multi-hexagon

• partition & frames

  • check all partition macroblocks and b-frame options
  • b-frame direct mode - auto

• bitrate

  • depends highly on the nature of the content (e.g., cartoons / screencasts achieve much smaller bitrates for the same quality settings)

  • alternatives methods:

    1. single pass - QQ (average):

       20 is very good 30 is aggressive (no noticeable artifacts)

    2. twopass - average bitrate (e.g., note that this is more of a recommendation than a hard setting. I think the first pass analyzes the variable bit rate for various parts and second pass sets the QQ to line up with your expectations)

Note that the final encoding is very CPU intensive. On my system, utilizing 2 cores the encoding with these settings is 20 fps.

11) Uploading

Blip.tv lets you upload pre-encoded video files directly, bypassing their transcoder. You'll need to repackage the AVI into an FLV file. At the time of writing, Avidemux didn't support H264 in FLV so you'll need to save as an AVI and then use ffmpeg to repackage the stream into an FLV:

		ffmpeg -i path/to/file.avi -vcodec copy file.flv