Wistia & Vimeo
captions and AD,
in plain language.

Short answer: Wistia accepts SRT and VTT only (TTML/DFXP/SCC are not accepted). Vimeo's official help-center docs list WebVTT and SRT. Both platforms have native audio description (AD) support, but in different ways and with different limits. Neither writes or mixes the AD audio for you; both expect a finished asset on upload.

Wistia (wistia.com) and Vimeo (vimeo.com) are the two largest hosted-video platforms outside YouTube for brand marketing. Both ship caption support out of the box and both publicly claim WCAG 2.1 AA conformance on their player. Where they differ is on audio description — the criterion most often misunderstood, and the one most likely to leave a brand short of the AA bar.

What caption file formats does Wistia actually accept?

SRT and VTT only. Wistia's troubleshooting help article is explicit: VTT files are converted to SRT on upload. DFXP, TTML, and SCC are not accepted. For brands that need a broadcast-deliverable caption file (SCC for FCC-regulated broadcast) or a premium-streaming master (TTML for Netflix-style delivery), the file has to come from somewhere other than Wistia.

Wistia's caption player ships with toggleable captions visible by default in the player chrome, which satisfies the WCAG 2.1 AA criterion 1.2.2 player-side requirements. The constraint is purely on what file formats the upload pipeline accepts. If the agency authored captions in TTML, the file has to be converted to SRT or VTT before it can land in Wistia.

Does Wistia support audio description natively?

Yes — with two caveats. Wistia offers both standard AD (narrates over existing audio) and extended AD (auto-pauses the video to narrate). Viewers can toggle the AD track from the player chrome; creators can set it to auto-enable for known accessibility-preferring users.

Caveat one: Wistia requires brands to upload a pre-mixed full-program audio file — that is, the AD upload must contain both the original audio of the video and the description narration, already blended. Wistia does not accept a description-only stem. The brand still has to do the mix; the platform just plays the result.

Caveat two: Wistia's audio description playback works only over HLS. If the player is serving an MP4 fallback (some older accounts, some browser configurations), the AD track will not play. The HLS-only constraint is documented in Wistia's help center and worth flagging in the QA pass after upload.

Accepted AD audio formats: MP3, OGG, WAV. Wistia's own managed AD service starts at $8/min human-reviewed (5-business-day turnaround) or $1/min AI-generated (completed within hours). That pricing applies if a brand opts into Wistia producing the AD; the underlying constraint — pre-mixed full-program file — applies regardless of whether the asset is produced by Wistia or by an outside vendor.

What caption file formats does Vimeo accept?

WebVTT and SRT. Vimeo's official help-center troubleshooting article lists those two formats; WebVTT is the recommended option. Some older third-party guides claim broader support (SCC, DFXP, SBV); the current Vimeo help center documents only the two.

Practical implication: a brand that needs a single caption asset that works on both Vimeo and a broadcast handoff still needs to author or export SCC separately. Vimeo will host the VTT for web; the broadcast vendor will need the SCC. Same captions, two formats — which is why authoring tools (Post Slate, and a few agency-side workflows) export multiple caption formats from one source.

How does Vimeo handle audio description?

Vimeo supports audio description via the platform's Multiple Audio Tracks feature. When uploading an alternate audio track, the creator picks a Type: Dubbed audio, Audio description, or Commentary. Viewers select the AD track from the player's audio menu.

Audio file formats accepted: WAV, M4A, AAC, MP3. MP4 also works — Vimeo extracts the audio. Unlike Wistia, Vimeo accepts a separate audio track (the description plus the original audio re-mixed, or the description in a complete program-replacement track) rather than requiring a pre-blended full-program file. Authors who write and mix AD themselves typically deliver the full alternate track here.

Plan caps matter. Vimeo's additional-audio-track caps are plan-gated: Free 1, Starter 5, Standard 10, Advanced 15, Enterprise 50 additional tracks per video. A brand on Vimeo Free can only carry one extra audio track — meaning the brand picks AD or a Spanish dub, not both. For a multilingual catalog, the plan upgrade is sometimes the real cost driver, not the AD production itself.

Do these platforms actually meet WCAG 2.1 AA?

Both platforms publicly claim WCAG 2.1 AA conformance on the player. Wistia's accessibility help page: "Our player complies with WCAG 2.1 AA." Vimeo's accessibility page: "Vimeo strives to conform to the Web Content Accessibility Guidelines (WCAG) 2.1 Level AA," with the new player engineered to meet WCAG 2.2 AA criteria. Wistia ships a 7-point accessibility grader covering screen reader compatibility, keyboard reachability, contrast, alt text, visible play, captions enabled, and AD support.

The catch: neither platform's accessibility page links to a current third-party-audited VPAT (Voluntary Product Accessibility Template) or ACR (Accessibility Conformance Report). Both use "strives to conform" / "complies with" language, which is the platform's self-assessment. That is fine for most brand procurement — both platforms have credible accessibility teams — but it is not the same as a third-party-audited report, and brand legal teams running formal procurement reviews sometimes ask for one.

What if my video airs on broadcast and lives on Vimeo?

You need different caption files. SCC for broadcast handoff (FCC-regulated under 47 CFR § 79.1, embedded CEA-608 or sidecar SCC). WebVTT for Vimeo and Wistia. TTML if the same content also ships to a premium SVOD platform. Same captions, three formats.

The authoring path that scales: write the captions once in a tool that exports all three (Post Slate's package is one option; some larger agencies have in-house pipelines that do this). Then upload the VTT to Vimeo, hand the SCC to the broadcast vendor, and the TTML to the streaming partner. Doing it that way avoids the conversion-bug surface that comes from authoring in one format and converting to others by hand.

Neither Vimeo nor Wistia accepts SCC. That is consistent with the broader pattern: web-video platforms speak VTT and SRT; broadcast-delivery vendors speak SCC; premium-SVOD speaks TTML. The platforms are not converging on a single format, and authoring tools have to bridge the gap.

Three things to check before you upload

1. Match the caption file to the platform's accepted formats. Wistia: SRT or VTT. Vimeo: WebVTT or SRT. If your authoring tool produced TTML or SCC, convert before upload — the upload pipeline will not.
2. If you are using Wistia's AD, pre-mix the full-program audio file. Wistia requires the AD upload to contain original audio plus description blended. A description-only stem will fail upload validation. Confirm the export is full-program before clicking through.
3. If you are using Vimeo's AD, check the plan's audio-track cap. Free is 1 additional track; Starter is 5; Standard is 10. If a brand has Spanish dubs and an AD track and a director's commentary track per video, the plan cap is the actual constraint — not the AD production.

Editor's note. Prepared by The Slate, Editorial. Published 11 May 2026. Reflects Wistia and Vimeo help-center documentation current as of writing. Platform specs change; confirm with the platform's current published spec before delivery. Wistia and Vimeo accessibility claims are platform self-assessments, not third-party VPAT reports.