How to record your Zoom meetings (for free) — Part 1

Part 1 explains how to record your Zoom webinars for free.

Photo by James Kovin on Unsplash

The pandemic has caused an explosion of webinars as professors and speakers are unable to travel to conference venues. But often times the webinars are held near midnight for your timezone, or at other times of the day where you just can’t be watching them. The best way to save them for later is to record them on your computer. You can also share them with colleagues who didn’t get a chance to attend. This is a 2 part article with part two here.

What you’ll need to have installed:

• Windows 10
• OBS Studio, download at the official page here.
• At least 2 GB disk space free for recording (1 hr can reach 1 GB before compression)

Setting up OBS PROFILE:

Create a new profile and name it, then go to Settings and ensure:

• Output format mkv. This is so that if the recording is interrupted by a computer crash, you won’t lose the whole recording, unlike mp4 files that need the recording to complete.
• Audio sample rate 48 kHz
• Set Desktop Audio to whatever speakers you are using. For example, mine was Conexant SmartAudio HD , which is what my computer comes with.
• Video set to 1280x720 for both Base Resolution and Output Resolution. Even if your screen is bigger, we are going to compress down to 1280x720 anyway.
• Downscale Filter set to Bicubic
• FPS 30. Later, we are going to downsample to 24 FPS, which is the mininum for human eyesight.

My profile can be downloaded here https://github.com/glycoaddict/obs-settings/blob/main/middle_res/middle_res.zip (click view raw to download)

Setting up OBS SOURCES:

First, create a Display Capture, which you can use to capture the whole screen. This is useful when the Zoom webinar is switching between many shared screens and the dimensions keep shifting, because OBS sometimes has trouble keeping track of the Zoom window.

Second, create a Window Capture, setting the window to your Zoom meeting. Note that each time you start OBS to begin a new recording, you may have to edit this Window Capture to ensure the correct Zoom window is selected. This is because Zoom calls its meetings and webinars by different names.

Your video sources should look like this. You can use the eye icons to choose which you are wanting to show.

Audio is a bit trickier. You need to record desktop audio to get the sound coming from the Zoom meeting. And you also need to record your Microphone if you are going to be speaking.

To configure your desktop audio, start playing a Youtube video in the background to check that you can detect the desktop audio. If the sound levels aren’t dancing about, click the cog icon and choose the correct device. Do the same for the Microphone and test to make sure it is working.

The Secret Sauce for microphone recording is in the filters. Click the cog and choose Filters. Using the plus “+” icon, create these three filters with the following settings. First, the Compressor will smooth out spikes in volume. Read the details here. The key parameter is the Ratio, which works well at 3:1, which can be thought of as “loud sounds will be dampened by 3x”. In practice this keeps the volume levels consistent so you don’t have to fiddle with the volume settings as you listen.

If you have a noisy background, you can actually set up an Expander filter that will “make quiet sounds quieter”. I.e. it focuses on the louder sounds. However, a simple noise suppression filter worked well for me because my environment was not so noisy, so we will use that.

Finally, you almost always need a Limiter, which ensures that any sound above a threshold is dampened. This irons out mic bumps and loud noises that cause distortion or pain to your ears.

By now, your Sources are all set up.

Test Recording

To validate our setup, create a Zoom meeting, hit Start Recording, and speak into the Mic.

To access the Video file, go to File > Show Recordings. By default it will open your Videos folder where your new .mkv file is saved. OBS uses date time stamps as file names so if you cannot find your video file, just sort by date and find the latest file. Play that .mkv file (you may need VLC) and check the video and audio are working as expected.

Next Step — Video Format

Before you archive this video or share this video with others, you need to fix two things.

• We recorded as .mkv so that interruptions wouldn’t destroy the whole recording. But phones and computers don’t like .mkv files. They prefer a more common format like .mp4
• At about 1 GB/hour filesize, the file is too large for sharing over whatsapp and you don’t want to be “wasting” disk space when there are more efficient file formats.

We’ll solve this in the next post by converting the video file to .mp4 and with a reduced filesize.

Take note of the file size of your video. Generally the video is

OBS to record. Settings. mkv format to protect against interruption.

But problem is of large size. So, sending via whatsapp is not possible.

01:07:44 -> flv 821 MB -> mp4 105 MB

00:51:00 -> mkv 978 MB-> mp4 90 MB -> split into 1/2

Compress using ffmpeg takes just a few minutes. inspired by https://superuser.com/a/960721 and this, and some tweaks I added myself, like setting the variable in Powershell.

Set-Variable -Name "filename" -Value '.\myfile.mkv'; Set-Variable -Name "outfile" -Value ([System.IO.Path]::GetFileNameWithoutExtension($filename) + ".mp4") ; ffmpeg -i "$filename"  -vcodec libx264 -preset slow -acodec libmp3lame -s hd720 -crf 18 -r 24 "$outfile"

How to get ffmpeg https://www.gyan.dev/ffmpeg/builds/ https://www.wikihow.com/Install-FFmpeg-on-Windows

Formats natively supported for Mac https://support.apple.com/en-us/HT201290 “QuickTime movie files (.mov), most MPEG files (.mp4, .m4v, .m4a, .mp3, .mpg), some AVI and WAV files”

This copy is an instant split! takes no time at all.

ffmpeg -ss 00:25:00 -i .\input.mp4 -vcodec copy -acodec copy .\output.mp4

For more reading https://opensource.com/article/17/6/ffmpeg-convert-media-file-formats

ffmpeg -to 01:02:00 -i '.\2021-04-21 16-29-11.mkv' -vcodec libx264 -preset medium -acodec libmp3lame -s 1024x576 -r 24  'neerja_preso.mp4'

The above was able to compress a 1 hour 3.6 GB mkv file that was recorded at high resolution 1600x900 and 30 fps and bitrate 7119 kb/s into a 96 MB mp4 file at 1024x576 and 24 fps with bitrate 79 kb/s. Worked fine on my 1600x900 screen resolution with no perceptible loss of quality!

Original file was 1376 MB

1600x900 -> 50 MB

1024x576 -> 37 MB