Video conversion (so you need a smaller file...)

When recording lectures I use one of two tools:

1) The automated lecture recording software provided by the university
2) Bbflashback on my surface

The first option has the advantage everything is done for you and an email turns up in your inbox with links to whatever you might want (a low quality, high quality and audio only recording).  The disadvantage is that even the low quality recording is pretty large, at around 100Mb for a 50 minute lecture.  For students based on campus the large file size isn't a problem.  For extramural students it is a different story, as their internet connection isn't necessarily reliable or fast.

The second option works well if you want a smaller recording and gives much more control (but I am having problems getting decent noise-free audio).  As bbflashback records only changes to the screen (rather than multiple frames a second) you can end up with a much smaller file size (e.g. 15 Mb for a 50 minute lecture).  This assumes you export with a very low frame rate and relatively low quality (but it makes for a perfectly viewable recording).  It also assumes you are using something like power point or writing on the tablet, rather tha playing video footage.

For some courses I use both, using the automated recording as a backup.  This was helpful this week when I accidentally hit the "discard" rather than "save" button after recording a bbflashback lecture.
All was not lost because of the automated recording but I really wanted to convert it from a 100Mb file to something smaller.

After a bit of research I settled on a video conversion tool called Handbrake: http://handbrake.fr/  (open source and available for free).

This read my mp4 recording in with no issues and then I set about to tweak settings to see if I could export it as a smaller file.  Almost everything I tried in terms of optimisation resulted in an approximately 60Mb file.  Tweaking different video settings didn't make much difference (I tried scaling the video size to half the original size, going to greyscale, using higher compression, longer encoding time, lower quality and nothing brought the size down by more than a Mb or two).

In the end I concluded that if altering the video didn't change things much then maybe I should play with the audio instead.  After all, a 3 minute song can easily be 3Mb, so an hour of audio could account for a lot of that 60Mb file size.  Turns out this hunch was right on the money.  By dropping down from 128bps to 64bps I was able to reduce the file size to 33Mb. 

The lesson is if you want to reduce your video recording file size, try downgrading the audio quality, you may be pleasantly surprised how much of a space saving that gives you (with no loss of intelligibility for spoken word)