Strangely inflating file sizes for Canvas Studio recordings

[daschaich]

When I record roughly 10-minute videos in Canvas Studio and download them as soon as they are processed, each one is roughly 40--50MB in size.  If I forget to do this immediately and come back to it later (specifically once the captions are generated), the same video somehow always inflates to a much larger file size, typically ~200--300MB.  This not only wastes large amounts of storage space and bandwidth, but more significantly may be an obstacle for students with limited connectivity.

Is this a known problem?  Is there any way to prevent or correct it?

In case it may be relevant, I am using Canvas Studio in Chrome 85.0.4183.83 on Slackware Linux, so the only video recording option it gives me is Webcam capture.  I am an instructor recording asynchronous material for a university course.

[Chris_Hofer]

Hello there, @daschaich ...

This is interesting.  I am going to take a wild guess here...and that's all it is...a guess.  After you have recorded your video in Studio and it has processed, do you ever play the video to see what it looks like?  If so, does the video picture quality appear somewhat blurry/pixelated and not real clear?  Then, if you come back to that same video later on (let's say a day later), does the video quality look much better?  I've found that when I first upload videos to Canvas Studio, the video quality isn't as sharp as I'd expect it to be.  But, if I wait a day, then the video quality is much better, and I've just chalked this up to the Studio servers needing a bit of extra time to fully process the video.  So, if your download file size is somewhat small initially but then larger later on, I wonder if it has to do with the video quality that I've described.  Again, just a hunch on my part.  Hope it might be of some help to you.  Take care...

[daschaich]

Thanks for the guess @Chris_Hofer .  At least to my eye there is no visible change in quality, which is why I'm eager to reduce the inflated file sizes.  A colleague of mine recommended HandBrake as a tool to reduce file bloat, but so far I've only been able to gain ~30--40% decreases with that program.  (For example, the ~260MB vs. ~45MB pre-HandBrake comparison above turns into ~170MB vs. ~30M post-HandBrake---still an apparently wasted factor of 6.)  This colleague reported "perfect videos" for less than 200MB per hour of recorded material (so ~30MB per 10minutes).

As another benchmark, for my previous (pre-Canvas) course I recorded Zoom calls, which gave me comparable quality from file sizes around 10MB for ~10minutes!  This is not really a fair comparison because the Zoom recordings focused on screenshared slides rather than Webcam capture, so I was content with the initial ~40--50MB from Canvas Studio.  But if the danger of ending up with ~200--300MB is ever-present, I will probably go back to Zoom for recordings and upload the resulting file to Canvas Studio for auto-captioning.

[daschaich]

I sent this question off to my institution's Canvas Support Team over the weekend, and just received this explanation:

The reason for the inflated file size actually has to do with the quality of transcoding. We first transcode the video when its uploaded to studio at its lowest setting and then go on and transcode the video to its higher settings. If you download the video early on you will get a smaller video file because of the lower transcoding quality. If you download it later like after the captions have been generated which in this case is after the higher quality transcoding setting has been generated then the file will be larger and better quality. Studio Defaults to downloading the highest possible quality of video when downloading. This won't have any effect on streaming the video through canvas as there are multiple quality settings for different connections.

While the streaming adjustability is reassuring, I plan to stick with Zoom recordings going forward.  I ran some (fair) comparisons over the weekend, finding that the files produced by Zoom remain ~5x smaller than those produced by Canvas Studio---even after I upload the Zoom file to Canvas Studio for captioning.  (As always, this is with no visible change in video quality to my eye.)  Zoom will also allow me to record screen-capture videos, which Canvas Studio doesn't seem able to handle on my system.

I'll leave the question 'unsolved' in case somebody might come along in the future to explain how to choose between the different video sizes when downloading.

[Chris_Hofer]

@daschaich ...

Thanks for posting that feedback from Canvas Support.  I'm glad to see that my suspicions were confirmed by that information.  Very helpful!

As far as I know, there is no way to choose what video file size to download.  It sounds like it's more of a timing thing on the end-user side at this point.