Platform reference · BigBlueButton · Moodle · Greenlight · EU Public Sector · EAA · GDPR

BigBlueButton captions: open-source web conferencing, Moodle integration, EU public-sector compliance

BigBlueButton (BBB) is the dominant open-source web conferencing platform for universities, Moodle LMS deployments, EU public-sector institutions, and organisations that need GDPR-compliant self-hosted or managed-SaaS meeting infrastructure. Where Zoom and Webex are commercial SaaS, BigBlueButton is open-source software that institutions deploy on their own servers (or via managed hosting through partners such as Scalelite, HostBBB, or edu-sharing) with full control over where meeting data and recordings live. The captioning surfaces — live CART integration, presentation recording, Greenlight scheduling portal, and the Moodle/LTI plugin — all feed into the same training-video compliance obligations that apply to any institutional webinar or lecture-recording surface: EAA, AODA, ADA Title II, and Section 504. The open-source model gives institutions maximum control over recording workflows — which means the captioning workflow is also the institution's responsibility to implement correctly.

TL;DR

A BigBlueButton captioning workflow spans four surfaces. (1) Live closed-caption room — BBB's built-in live CART caption panel, where a designated captioner types in real time and the captions display to all room participants. (2) Presentation recording — BBB records the presenter's slides, webcam, screen share, and audio; the recording plays back in the BBB playback portal with a built-in subtitle capability that requires a separately uploaded WebVTT or SRT file. (3) Greenlight — BBB's scheduling and room-management frontend; recordings published through Greenlight inherit the playback portal's caption handling. (4) Moodle BigBlueButton plugin — Moodle's native BBB integration (available since Moodle 4.0 as a core activity module) launches BBB rooms from within a Moodle course and can surface recordings inside the Moodle course interface. The caption file attached to the BBB playback recording is what displays in Moodle's embedded recording. The proper-noun failure mode is structural: BBB does not have its own built-in STT auto-captioning engine (unlike Zoom or Teams); captions must be either typed by a live CART captioner or produced and uploaded as a post-meeting caption file. Which means the captioning quality is entirely determined by the institution's post-meeting workflow.

BigBlueButton deployment types and their caption implications

BigBlueButton's open-source model means the deployment shape varies widely:

Self-hosted single-node (common at SMB universities and EU research institutes). The institution runs BBB on its own Ubuntu server(s). Recordings are stored on the BBB server's local filesystem. The institution controls all recording data and caption files. GDPR data residency: recordings never leave the institution's infrastructure, which is the strongest possible data-residency posture. Captioning workflow is entirely the institution's responsibility.
Self-hosted Scalelite load-balanced cluster (common at large universities and multi-campus institutions). Scalelite pools multiple BBB servers behind a load balancer, with shared NFS storage for recordings. Used by large-deployment institutions where dozens or hundreds of concurrent rooms are needed for live lectures. The recording and captioning workflow is the same as single-node; Scalelite adds operational complexity but not captioning-workflow differences.
Managed hosting (HostBBB, blindsidenetworks, eduSHARE, ISN, Netcup, etc.). Managed-SaaS BigBlueButton where the institution does not manage servers but retains data-residency guarantees because the managed host runs within the institution's or country's data boundary. Common in Germany (DSGVO-compliance-focused), Netherlands (AVG-compliance-focused), and EU public-sector tenants who need GDPR Article 28 data-processor agreements with their hosting provider. The captioning workflow is identical to self-hosted; the DPA governs recording data handling.
LTI-embedded via Moodle, Canvas, or Brightspace. BBB accessed through an LMS's LTI integration, where the LMS is the front door and BBB is the conferencing backend. Recordings surface back in the LMS course. Moodle's native BBB activity module is the most common form. Canvas and Brightspace use LTI 1.3 external tool configurations to embed BBB. The caption file on the BBB recording is what displays in the LMS-embedded recording player.

Surface 1 — Live closed-caption room (CART integration)

BigBlueButton has a built-in Closed Captions panel that any room participant with the caption-typer role can type into. The typed captions display in real time to all participants who have the closed-caption panel open in their BBB UI. This is the standard CART pathway in BBB:

The meeting organiser (via the BBB API or Greenlight) designates a participant as a caption typist before or during the session.
The caption typist opens the Closed Captions panel and selects a language.
The typist types live captions as the presenter speaks. All room participants can toggle the CC panel to see the captions.
Multiple language caption streams can run simultaneously (multiple typists, one per language).

BBB does not generate automated speech-to-text captions in the live session natively. A third-party STT integration (using the BBB API and a WebSocket connection) can inject automated captions into the CC panel — some institutions run a self-hosted Whisper or Vosk STT service that pushes automated captions into BBB's live CC panel. These automated-STT integrations have the same proper-noun failure modes as all generic STT systems, compounded by the latency and word-error-rate of the particular STT model chosen. A self-hosted Whisper large-v3 model running on the institution's GPU produces better accuracy than the defaults but still requires a glossary pass for technical proper nouns.

Live CART captions in BBB are the accommodation surface — the real-time caption display for participants who need captioning during the session. They are not, by default, stored as a caption file on the recording. The recording caption workflow (Surface 2) is the compliance artefact.

Surface 2 — Presentation recording and subtitle track

BigBlueButton records the presentation in its native format: a synchronised playback of the presenter's slides, screen share, webcam video, and audio. The recording plays back through BBB's HTML5 playback portal at a URL like https://bbb.institution.edu/playback/presentation/2.3/{meeting-id}. BBB playback supports a caption/subtitle track that the institution adds by uploading a WebVTT file to the recording's caption directory on the BBB server.

The caption upload workflow:

Produce a WebVTT caption file for the recording. BBB recordings have a downloadable audio track that can be used as the source for captioning. The audio track is the full session audio; the caption file must be time-coded to the recording's timeline (which typically starts at the moment the presenter began, accounting for pre-join and technical-check time).
Upload the VTT file to the BBB server. BBB recordings are stored under /var/bigbluebutton/published/presentation/{meeting-id}/. The caption file goes in the recording directory alongside the metadata.xml, shapes.svg, and the audio/video components. The specific path varies with BBB version; BBB 2.6+ and BBB 3.0 store captions under captions/ within the recording directory.
Update the recording's captions.json manifest (in BBB 2.6+) or the equivalent metadata in the recording directory to register the new caption track. The BBB playback player reads this manifest to know whether a caption track is available.
Verify in the BBB playback portal. Open the recording URL, click the CC button in the playback player (if visible), and confirm the caption track displays and is correctly timed.

For managed-hosting tenants, the caption-upload step typically requires SSH access to the BBB server or a hosting-partner API. Many managed-hosting providers offer a web panel for managing recordings; caption upload may or may not be exposed in the panel. Check with the managed-hosting provider for their recommended workflow.

For Moodle-embedded recordings, the caption track uploaded to the BBB recording directory is what displays in the Moodle BBB activity player when the recording is accessed from the course. The Moodle interface shows the BBB playback portal embedded via iframe; the caption file in the BBB recording directory is what the iframe-embedded player reads.

Surface 3 — Greenlight scheduling portal

Greenlight is BigBlueButton's official room-management and scheduling frontend, providing a web interface for creating BBB rooms, managing recordings, and sharing room links — replacing the need to interact with the BBB API directly. In Greenlight v3 (the current version), recordings published through Greenlight appear in the Greenlight recordings list and can be accessed via the BBB playback portal. Greenlight does not add a separate caption-management UI — the caption track is managed at the BBB recording-directory level (Surface 2). The Greenlight recordings list links to the playback portal URL, where the CC button will appear if a caption track has been uploaded.

For institutions using Greenlight as their primary BBB frontend (typical at SMB universities and research institutes that are not deep Moodle users), the caption workflow is: produce VTT from recording audio → upload to BBB recording directory → verify in Greenlight playback link.

Surface 4 — Moodle BigBlueButton plugin integration

The Moodle BigBlueButton activity module (core since Moodle 4.0; available as a plugin for earlier versions) integrates BBB rooms directly into Moodle courses. Students join BBB sessions by clicking the activity in their Moodle course; they are launched into the BBB room. Recordings from Moodle-launched BBB sessions surface back in the Moodle activity as "Recordings" that students can access from the course. The recording player embedded in Moodle is the BBB HTML5 playback portal, displayed in an iframe.

The caption state in Moodle-embedded BBB recordings is determined by the BBB recording directory, not by Moodle. Moodle does not have a separate caption-upload UI for BBB recordings; the caption must be added to the BBB recording directory (Surface 2). When a student clicks a recording in the Moodle course activity, the iframe loads the BBB playback portal URL; if a caption track was uploaded to the recording directory, the CC button appears in the player and the caption track is accessible.

The connection to the Moodle captions reference: Moodle supports multiple video surfaces in a course — the H5P interactive video module, URL/oEmbed external video, and the file-resource sidecar VTT path — but the BBB activity module's recordings are a distinct fourth surface, handled through the BBB recording directory rather than Moodle's file manager or H5P. For a Moodle deployment where BBB provides the primary live-session recording surface, the BBB caption workflow is the most important captioning workflow for instructional video in that deployment.

Compliance regimes — BigBlueButton at EU public-sector and university tenants

EAA (European Accessibility Act). EU public-sector institutions using BBB for training or public services are bound by the EAA since 2025-06-28. Video published to employees or the public via BBB recording URLs falls within EAA product/service scope if it constitutes an "audiovisual media service" or an accessible-information service. The captioning standard is EN 301 549 clause 7.1.1–7.1.5 — synchronised captions on prerecorded video, with substantive accuracy and proper presentation characteristics.
GDPR / national implementing law. BBB's self-hosted deployment is the strongest GDPR data-residency posture: recordings and caption files never leave the institution's infrastructure. Managed-hosting deployments require a GDPR Article 28 DPA with the managed-hosting provider. The external captioning service that produces the caption VTT (when recordings are shared with a captioning vendor) is a sub-processor and requires its own DPA addendum. GlossCap's DPA addendum for GDPR Article 28 sub-processing is available on request.
AODA. Canadian universities using BBB (common among open-source-LMS-preferring Canadian institutions using Moodle + BBB) are bound by the Ontario IASR § 14 captioning obligation. Three-year compliance reporting cycle; next major large-organisation filing window 2026.
ADA Title II. US public universities using BBB — particularly those running self-hosted Moodle + BBB for GDPR-aware distance-education programmes or international partnerships — bound to WCAG 2.1 AA on web content including training video. OCR has sampled recording captions from LMS-embedded video in investigations; BBB recordings embedded in Moodle courses are in scope.
Section 504. US institutions receiving federal financial assistance. BBB recordings used in instructional, training, or programme-relevant contexts must have substantively accurate captions. Individual accommodation needs (documented hearing-related needs in an IEP or 504 plan) trigger immediate captioning obligations for BBB sessions that student attends.

Proper-noun failure modes in BigBlueButton recording content

BBB recording content spans the university and EU public-sector spectrum. The most common proper-noun failure categories:

EU legal and regulatory vocabulary. GDPR and implementing legislation (DSGVO, Loi Informatique et Libertés, LGPD), ePrivacy Regulation, PSD2, NIS2, DSA, DMA, DORA, MiFID II, EMIR, Schrems II. EU regulatory body names (EUIPO, ENISA, EBA, EIOPA, ESMA, EDPB, EFSA, EMA, ERA, ERA). Citation patterns (Regulation (EU) 2016/679, Directive 2019/882, Implementing Decision (EU) 2018/1523). These appear in EU public-law, regulatory-affairs, and compliance-training BBB sessions.
Member-state regulatory vocabulary. Germany: DSGVO, TTDSG, Datenschutzkonferenz, BfDI, BDSG, BSI Grundschutz, Sozialgesetzbuch. Netherlands: AVG, Autoriteit Persoonsgegevens, Wmo, Wet langdurige zorg. France: Loi Informatique et Libertés, CNIL, DSA national enforcement. These appear in member-state-specific compliance-training content.
Higher-ed discipline-specific vocabulary. Physics and chemistry nomenclature (IUPAC names, molecular formula pronunciation), mathematics notation (eigenvalues, Lagrangians, manifolds), computer science (algorithms, data structures, specific programming languages and frameworks), medical and life-science vocabulary when used in university research training. Detailed by discipline in the Canvas LMS captions reference.
Open-source software ecosystem. BBB is commonly used by institutions that prefer open-source software broadly — Moodle, NextCloud, Jitsi, Nextcloud, Collabora Online, LibreOffice Online. The corresponding vocabulary: Moodle module names, Nextcloud app names, LDAP/Shibboleth/eduGAIN identity-federation terms, OAI-PMH, DSpace, OpenMRS, OMERO. These appear in IT-administrator training sessions and open-source-community educational content.
Language diversity. EU public-sector BBB deployments frequently operate in multiple languages — German, French, Dutch, Italian, Spanish, Polish, Swedish — with code-switching between languages in multilingual sessions. Self-hosted STT integrations face compounded accuracy challenges when the language switches mid-session.

The BigBlueButton recordings retrofit pattern

For an institution sitting on a BBB server with a back-catalogue of recordings without caption tracks:

Inventory. Use the BBB API (getRecordings endpoint with appropriate filters) to enumerate all recordings by meeting name, room, date range, or metadata tag. BBB recordings have a playback URL and associated metadata. Most university BBB deployments find that 20–50% of recordings were from instructional sessions (courses, training workshops, orientation events) that have ongoing compliance obligations.
Triage. Prioritise by instructional exposure: recordings linked from an active Moodle course assignment, recordings accessible to students via a published Greenlight link, recordings from documented-accommodation-student sessions. Recordings from informal staff meetings with no student-facing distribution can be archived rather than captioned. The triage pass typically reduces retrofit scope by 40–60%.
Audio extraction. For each triage-selected recording, extract the audio track from the BBB recording package. BBB recordings store audio as a separate WebM or Opus/Ogg audio file in the recording directory (audio/audio.webm or similar in BBB 2.6+). The audio file is the input to the captioning service.
Caption production. Produce a glossary-biased WebVTT caption file from the audio. The institutional glossary — EU legal vocabulary, discipline-specific terms, open-source software names, member-state regulatory citations — is built once and applies to every recording in the catalogue.
Upload and verification. Upload the VTT to the BBB recording directory. Update the recording's captions manifest. Verify in the BBB playback portal that the CC button appears and the caption track is correctly timed. For Moodle-embedded recordings, verify in the Moodle course activity that the CC button is accessible.
Log. Asset register: BBB meeting ID, recording ID, Moodle course ID (if applicable), caption file version, caption source (GlossCap, CART, manual), upload date, reviewer name and date. The register is the EAA, AODA, and ADA Title II compliance artefact.

See pricing

FAQ — BigBlueButton captions

Does BigBlueButton have built-in auto-captioning?

Not natively in the standard BBB distribution. BBB's Closed Captions panel requires a human typist (CART captioner). Some institutions add a third-party STT integration via the BBB API — typically a self-hosted Whisper or Vosk model that pushes automated captions into the CC panel in real time. These integrations have the same generic-STT accuracy limitations (80–90% on conversational audio, materially lower on technical proper nouns) as any other auto-caption system, and require a glossary-biased correction pass for the recording caption file even if the live captions were automated.

How does the Moodle BBB plugin relate to Moodle's other video caption surfaces?

Moodle has several video surfaces: the file-resource sidecar VTT path (for video files uploaded directly to Moodle), the H5P interactive video module (which uses a WebVTT file inside the H5P package), URL/oEmbed external video (YouTube or Vimeo embeds), and the BigBlueButton activity module's recordings. Each surface has its own caption-delivery mechanism. The BBB recording caption is managed in the BBB recording directory and delivered through the BBB playback portal iframe. The Moodle captions reference covers all four surfaces together.

Is BigBlueButton GDPR-compliant for European institutions?

A self-hosted BBB deployment is fully GDPR-compatible — all recording and caption data stays within the institution's infrastructure, no cloud processing occurs by default, and there is no sub-processor to sign a DPA with for the recording storage itself. The only GDPR sub-processing obligation that arises is when the institution shares a recording with an external captioning service for post-meeting captioning. At that point, the captioning service is a sub-processor under GDPR Article 28 and must sign a DPA. GlossCap operates under a GDPR Article 28 DPA; your institution's legal or privacy team will need to review and sign the DPA before recordings can be shared.

Does the EAA apply to our BBB deployment if we are an EU public university?

If your institution is an EU public-sector body (Öffentliche Stelle in German law, organisme public in French, etc.), EAA requirements for public-sector digital services — which largely follow the EU Web Accessibility Directive (Directive 2016/2102) and the related Implementing Decision (EU) 2018/1523 — apply to your web-accessible video content. Additionally, if your institution offers services to private-sector customers or to the general public beyond the traditional public-service scope, the full EAA product/service scope under Directive (EU) 2019/882 may apply. In either case, video accessible via the BBB playback URL or embedded in a public-facing course platform must have substantively accurate captions per EN 301 549 clause 7.1.1–7.1.5 and the WCAG 2.1 AA captions criteria.

How does BigBlueButton compare to Zoom and Webex for university deployments?

The key differences for captioning: BigBlueButton's self-hosted model gives institutions maximum data-residency control (GDPR advantage, no recordings leave the institution's servers), but requires the institution to implement the captioning workflow entirely — BBB has no built-in STT auto-captioning. Zoom and Webex have built-in STT auto-captioning that produces a draft transcript automatically, but that draft has the proper-noun failure mode that requires correction. BBB institutions that implement a post-meeting captioning workflow (extract audio → glossary-biased caption → upload VTT) may end up with better-quality captions than institutions relying on Zoom or Webex auto-transcripts that are never corrected.