Converting BBB recordings to MP4 with Webcam on Deskshare Movie

Convert your BBB recordings to a compressed MP4 stream with webcam overlay and logo.

Similar to several other academic institutions, we are hosting our own Big Blue Button Server (BBB). This is an open-source and free conference and teaching server tailored for academic environments. The standard player showing recorded teaching session is fairly simple and does not allow to download a video stream (e.g. MP4). However, the necessary files - movie of the shared desktop/presentation and webcamera - are stored on the BBB server and can be converted with ffmpeg to a combined stream. Also, ffmpeg allows to apply audio-filtering steps that will enhance audio quality.

The next steps are tailored towards combining shared desktops and webcameras and applying a FFT-based noise canceling and speech filter (afftdn). We experimented with different low- and high-pass filtering options, but found this to be most useful. If you have a particularly noisy audio stream, you may need to filter this manually or use audacity.

These steps also allow you to convert existing recordings. If you plan to record new, high resolution recording, please look at OBS.

On the BBB server change to the directory that contains the processed and published recordings. These are usually stored in /var/bigbluebutton/published/presentation/. Change directory to the meeting id of the recording - these are usually long digits and number combinations that you see in the http address when playing the recording (e.g., bda894a68f6d2aa38dc62dd788e19d357e17948c-1603807633429.)

First, extract audio from webcam stream (stored in video/webcams.webm), filter audio with afftdn, and combine with desktop stream (stored in deskshare/deskshare.webm). We convert the WEBM format to MP4.

ffmpeg -nostdin -threads 4 -i video/webcams.webm -i deskshare/deskshare.webm -af afftdn deskshare_with_sound.mp4

Next, reduce size of video recording by 1/4 (scale by 4). This depends on your video resolution, we are currently using a resolution of

video_output_width: 640
video_output_height: 480

set in /usr/local/bigbluebutton/core/scripts/presentation.yml.

ffmpeg -nostdin -threads 4 -i video/webcams.webm -vf "scale=iw/4:ih/4" webcams_sc4.mp4

Add scaled webcam stream and deskshare video and place webcam stream in upper right corner (often referred to as ‘picture in picture’):

ffmpeg -nostdin -i deskshare_with_sound.mp4 -vf "movie=webcams_sc4.mp4[inner]; [in][inner] overlay=W-w:0 [out]" completed_ur.mp4

We also add the Institute of Geoscience logo to the upper left corner. We scale the (almost) squared logo to 100x100 pixels.

ffmpeg -nostdin -i completed_ur.mp4 -i geowiss__cmyk_blue_2000px.png -filter_complex "[1:v]scale=100:100[v1];[0:v][v1]overlay[outv]" -map "[outv]" -c:a copy -map 0:a completed_ur_logo.mp4

This file is now ready to be uploaded to a media server for further distribution!

Note that the following video has been downscaled to 640x360 (from 1280x720) with ffmpeg: ffmpeg -nostdin -ss 00:18:06 -i completed_afftdn_ll.mp4 -t 00:05:00 -vf scale=640:360 -vc copy NB_linearregression.mp4

Here is a high-res link to a Media-UP recording of an entire lecture:

A Shell script combining these steps:

#!/bin/sh
# Convert the deskshare and webcam to a combined video stream including logo
# cd /var/bigbluebutton/published/presentation/
meetingId=$1
cd $meetingId

# add webcam sound to deskshare
ffmpeg -nostdin -threads 4 -i video/webcams.webm -i deskshare/deskshare.webm -af afftdn deskshare_with_sound.mp4
ffmpeg -nostdin -threads 4 -i video/webcams.webm -vf "scale=iw/4:ih/4" webcams_sc4.mp4

#add picture in picture
ffmpeg -nostdin -i deskshare_with_sound.mp4 -vf "movie=webcams_sc4.mp4[inner]; [in][inner] overlay=W-w:0 [out]" completed_ur.mp4

# add logo in upper right corner (could be combined with previous command)
ffmpeg -nostdin -i completed_ur.mp4 -i /var/bigbluebutton/published/presentation/geowiss__cmyk_blue_2000px.png -filter_complex "[1:v]scale=100:100[v1];[0:v][v1]overlay[outv]" -map "[outv]" -c:a copy -map 0:a completed_afftdn_ll.mp4

rm -fr deskshare_with_sound.mp4 webcams_sc4.mp4 completed_ur.mp4