FAQ: Using BigBlueButton

Adapted from the official BigBlueButton Documentation.


Does BigBlueButton offer permanent sessions?

The BigBlueButton server does not support persistent or permanent sessions where users can leave and return the next day, for example, and have their slides and chat messages persist.

This is by design. Why is this the case? This design makes it easy for system administrators to upgrade or replace a BigBlueButton server without migrating/updating any database. As an analogy, the BigBlueButton server works like a web server. When loading content from web server, you don’t tell a web server “I need to load a file at 2:00 PM tomorrow”; rather, you just load a file when needed. The web server responds to the request and, when finished, it forgets about the request and moves onto the next.

It’s similar with the BigBlueButton server. The lifespan of a session on the BigBlueButton server begins when a front-end sends a create API request to the BigBlueButton server. Once a room is created (the create request succeeded), users can join the session and interact within the session. The session ends (and is cleared from the server’s memory) when the last person leaves, whereupon BigBlueButton clears the session from memory.

Screen Sharing

What is needed to run desktop sharing?

BigBlueButton using WebRTC for sharing audio, video, and screen. You should be able to share your screen using Chrome, FireFox, and the newest version of Edge (based on Chromium). You don’t need to install any plugin or download any additional binary to share your screen.

At the time of this writing, you can view the presenter’s screen on mobile devices, but not share the mobile screen.

Can I share a specific window when sharing my desktop?

While you can’t choose a specific window, on Windows you can share a specific region of your desktop and place the window within that region.


Can I upload Microsoft Office documents to BigBlueButton?

Yes. BigBlueButton uses LibreOffice 4.3 for converting Microsoft Office documents into PDF for display in BigBlueButton.

If possible, for best results, save your Word or PowerPoint document as PDF. If you are using Office 2007, we recommend using Microsoft’s free download to enable Office 2007 to save any document to PDF.

You’ll always get the best results with PDF.

Will my animations in PowerPoint convert when uploading to BigBlueButton?

Since BigBlueButton must convert your PowerPoint document to PDF (using LibreOffice), none of the animations (visual or audio) will be converted. What you’ll see is a PDF page corresponding to the final state of each slide.

I uploaded a document but some fonts are missing after conversion!

If you upload a PDF document, all your fonts will come through with the document. In other words, for best results, if possible always create a PDF and upload it for conversion.

If you upload a Word or Power Point document that has special fonts, such as Chinese language, the document must first be converted by LibreOffice into PDF. Unless you’ve configured the LibreOffice server running within BigBlueButton to have the necessary fonts, then you will see empty spaces (or boxes) for the missing fonts.

Does BigBlueButton support mulit-user whiteboard?



I’m on Ubuntu and I can’t share my webcam!

See Ubuntu’s documentation for Webcam Troubleshooting.

Voice Conference

Why can’t others hear me in the voice conference?

If others in the voice conference don’t hear you when you speak, it’s likely that the browser has picked the wrong microphone on your computer. You can click the phone icon twice – once to leave and a second time to rejoin – to try joiing the audio again. When you see the echo test, if you can’t hear yourself, click “no” and select a different microphone.

Why do others only hear part of my audio?

FreeSWITCH has automatic audio clipping, which means it will not transmit a speaker’s audio if the volume is too low. If the speaker’s audio is low, FreeSWITCH might take a moment to recognize that someone is speaking before transmitting, causing others to hear your audio only after you have started speaking a few words.

Why is there an echo in the voice conference?

In BigBlueButton, the built-in acoustic echo cancellation is used, so in most cases, you should not hear any echo from remote users.

In any event, we always recommend that you have your remote users use a headset with microphone. This will ensure the best audio in a session.

If a remote user is using a laptop with a built-in microphone, you should not hear an echo. However, if two remote users are using laptops with built-in microphones and neither is using a headset and both are sitting close to each other (close enough for the microphone in one laptop to pickup the audio from the speakers in the other laptop), then you will hear an echo. The reason is the built-in echo cancellation only works with the audio coming from the host laptop – the audio coming from the second laptop will be picked up as an external audio source.

If a student is causing echo, the best way to solve this problem, if you are logged in as a moderator, is to mute the user by clicking the microphone icon to the left of their name.

Overall, the best solution is ask all users to use a headset – this will ensure no background noise or echo.

How do I get the best audio?

Use FireFox or Chrome.

Both these browsers support web real-time communications (WebRTC) audio. BigBlueButton will use WebRTC for audio if the user is on FireFox or Chrome browser.

Record and Playback

What parts of the session does BigBlueButton record?

BigBlueButton records all activity in the presentation, chat, webcams, and desktop sharing for playback.

What browsers support playback?

BigBlueButton supports playback in Chrome and FireFox.

In BigBlueButton, the audio from a recorded session is encoded into Vorbis, an open source audio format that is not patent encumbered. Playback of Vorbis audio is supported in FireFox and Chrome, but not IE and Safari.

BigBlueButton will playback the webcams from a session using the WebM container, which, thanks to Google, provides a high-quality open source video codec VP8. Playback of video in VP8 is supported by FireFox and Chrome, but not IE and Safari. See HTML5 video Wikipedia article.

What is the disk space usage for storing 1 hour of recordings?

The file sizes are for a one hour session. When a recorded session ends, BigBlueButton archives all the raw content, then runs the recording scripts to create a publish format (presentation).

Media Shared Archive Publish Total
audio 111 MiB/h 11 MiB/h 122 MiB/h
audio + webcam (1 webcam) 131 MiB/h 51 MiB/h 182 MiB/h
audio + desktop sharing 236 MiB/h 73 MiB/h 309 MiB/h


For audio, the storage of the audio stream is 110 MiB/h. The storage is a .wav file

For audio + webcam, the additional storage is for saving each individual webcam stream. A one hour webcam stream at the default resolution (320x240) is 20MiB.

For audio + deskshare, the additional storage is for the desktop sharing stream (there will only be one stream at any one time). A one hour desktop sharing stream is 125MiB.


For playback, the audio, webcams, and desktop share are processed into a single playback file WebM (VP8 Codec).

For audio only, the WebM file is 5.4MiB. There is an additional Vorbis Audio File that is 5MiB.

For audio + webcam only, there is a single webM file that is 51MiB

For audio + desktop sharing, there is a single WebM that is 72MiB.

Can I see the total time of the session?

The information displayed during playback is browser specific.

In Chrome, the audio playback component shows only the current time index for the playback. To see the overall length of the session, you can scrub to the end of the audio after the audio file has loaded.

In FireFox, the audio playback component shows both the current time index and total time of the audio file.

How do I download a recorded session?

When looking to download a recorded session, most expect a single link to download the video file.

In contrast, BigBlueButton does not create a video file for playback. Video files for a three hour lecture can get very large. Instead, BigBlueButton creates an HTML5 page that references PNG images and audio, and time indexes the PNG images against the audio to match their display in the session. The result is the source playback files are very small and can be hosted on any web server. The drawback is there will be a pause for the browser to download all this content, but, once downloaded, there is no more load on the web server.


BigBlueButton is designed to be accessible to users with visual and/or audible disabilities.

BigBlueButton supports both JAWS and NVDA screen readers. When using a screen reader, we recommend using Internet Explorer or the 32-bit version of FireFox. The 64-bit versions of FireFox and Chrome make it harder for screen readers to interact with the BigBlueButton client.

BigBlueButton supports live closed captioning. A stenographer can join the session and provide a live caption stream to all users (you can have multiple stenographers simultaneously providing captioning in multiple languages). Later on, when BigBlueButton processes the recording, it will convert the closed captions to subtitles in the playback.