Editing and enconding Zoom recordings

Good morning to everyone,
I am currently recording my lectures using zoom. I record only audio and the my screen share of the powerpoint presentation. I do not record my own zoom video as this creates much larger files sizes. I record my screen as I use a pointer and scribble on my presentations too.
Anyhow, there are parts of the lecture i would like to cut out, the start, end and some bits in the middle where i may be interrupted by wife or kid!
To do this I found a tool called Lossless Cut. It works very well, however…
The way zoom encodes the films results in very small files sizes with excellent quality. There are very few key frames, but when these are generated they are are of high quality. However, the lossless cut means that video playback only starts at the keyframe so I have to either cut sometime before I want, or the lecture starts with a black screen until the next keyframe is reached (which can be several seconds!)
I’ve tried to reencode the films in shotcut, but i cannot get anywhere near the original file sizes.
The best i got was using:
constrained VBR
buffer size to 60s
GOP 999
B frames 8
qscale 31

The video output is perfect, in that slide transitions are perfect. however, the file size is still twice as large as what zoom manages.

Any idea what advanced parameters i should be using to decrease the number of key frames?

I think this is an important issue with more and more people recording their lessons and sharing these with their students. File size is always important.


in summary, do not use hardware encoder and “crf=30, gop=249, B frames=8”

Hi, thanks for the quick reply!

I can confirm that disabling hardware encoding, results in correct file sizes, whereby the constrained VBR results in average bitrate i am targeting, 0.1MBit/s resulting in a final file size of 0.7MB/minute (with video only).

I may find time to test what influence GOP and B frame number has on quality and encoding times.

Increasing GOP from 250 to 999 resulted in only a slight gain in compression (5%ish), so not worth it, as this negatively impacts the ability to scroll through the file when watching.

The encoder being used is Libx265. May test 265 vs 265.


Hi, I had some problems with the zoom program. During this quarantine period, I used a lot this platform but one day it just gave me an error. I couldn’t open it. I have updated it twice but I still couldn’t open it. Because of that, I had to make a lot of presentations. I found one that is a root cause analysis template. I was able to make my presentations and to create my analysis during the quarantine. To be honest this is the easiest way of analysis that I have made. I was surprised when I found out that even my big boss appreciated this. So can you guys tell me what can be the problem with my zoom, maybe I have to insert code or something like that?

Starting with Shotcut 20.06 (soon to be released), there will be two export presets built-in called “Slide Deck (H.264)” and “Slide Deck (HEVC)” that are optimized for encoding Zoom and PowerPoint recordings along with audio.

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