Chromecast Local Video Subtitles: Four Ways to Cast Your Own Files with Captions

Why your subtitles disappear when you cast

When you cast a file rather than mirror a screen, the Chromecast plays the video itself. Your phone or computer only tells it what to load. That means the subtitle file must be in a form the Chromecast's player understands, delivered in the way it expects. Google's Supported Media page for Cast spells out the limits:

Subtitle and caption formats

TTML, WebVTT and CEA-608/708; SRT, ASS and SUB are not on the list

Delivery

Subtitle resources must implement CORS, a web server permission that lets the Chromecast fetch the file

Containers

MP2T, MP3, MP4, OGG, WAV and WebM; MKV is not in the list

Video codecs

Vary by model: first and second generation Chromecasts list H.264 up to 1080p at 30 fps and VP8, while Chromecast with Google TV and Google TV Streamer add HEVC and VP9, and Google TV Streamer also AV1

So a typical downloaded film, an MKV with an SRT beside it, fails on two counts before anything else is checked. Apps that cast such files successfully are doing work behind the scenes: converting SRT to WebVTT, serving it from your device with the right headers, and often remuxing or transcoding the video.

Diagnose by symptom

• The video casts, the subtitle option is missing. The app didn't send a subtitle track, usually because it doesn't support sidecar files or couldn't find yours.
• The subtitle option is there, nothing appears. The track was offered in a format or way the Chromecast couldn't load; with a home-made setup this is often the CORS requirement.
• The video won't cast at all or only plays sound. A container or codec the Chromecast model doesn't support, such as HEVC on a first generation device or an MKV the app doesn't remux.
• Subtitles show on the phone or laptop but not on the TV. You're watching the sender's local player; only some apps pass subtitles on to the cast session.
• Accents or non-Latin text look wrong. WebVTT must be UTF-8, so a file saved in an old Windows code page breaks after conversion.

The four ways to get subtitles onto the TV

Each route has a different trade-off; which suits you depends on how often you do this and what devices you have.

1. Mirror a Chrome tab. Open the video in a browser player that shows your subtitles, then cast the tab from Chrome's Cast menu. The Chromecast receives the tab as a video stream, so whatever the page shows, subtitles included, appears on the TV. Picture smoothness depends on your computer and Wi-Fi, and the computer has to stay on and playing.
2. Use a casting app that supports sidecar subtitles. Several phone and desktop apps load a local video plus a subtitle file and cast both, handling the conversion to WebVTT for you. Support for formats, MKV and styling varies, so check the app's own documentation.
3. Use a media server such as Plex. Plex fully supports SRT, SMI, SSA/ASS and WebVTT, embedded or as sidecar files, and recommends saving text subtitles as UTF-8. Its naming pattern is Movie Name (Year).en.srt beside the video. For image-based PGS and VobSub tracks, Plex says most apps need the video transcoded to burn the subtitles in.
4. Burn the subtitles into the video. The text becomes part of the picture, so any casting method, app or Chromecast model that can play the MP4 shows them. They can't be switched off, and each language needs its own file.

On a Chromecast with Google TV or a Google TV Streamer there's a fifth option: install a player app on the device itself and play files from a network share, so nothing is cast at all. Subtitle support then depends entirely on that app.

Converting SRT to WebVTT or TTML

If your app or home-made setup accepts a WebVTT or TTML file but not SRT, convert the file rather than renaming it. The differences are small but strict: WebVTT starts with a WEBVTT header line, uses a full stop instead of a comma before milliseconds, and must be UTF-8. The walkthrough on converting SRT to VTT shows the changes line by line.

Three no-install ways to get the right file:

• Import the SRT into the free subtitle editor and export VTT. The editor reads imported files as UTF-8, so fix the encoding first if the text looks wrong in the line list.
• For TTML, the SRT to TTML converter writes a timed-text file in your browser and shows a preview of the first lines before you download.
• If the subtitles are in an old code page, run them through the SRT encoding converter first; it previews the text under the detected encoding and saves UTF-8.

If the subtitles are inside an MKV, the free extract subtitles tool lists the file's tracks and saves a chosen text track straight to VTT. Image tracks (PGS, VobSub) can't be saved as text.

Two examples

Burning subtitles in for casting

The same free subtitle editor renders an MP4 with the subtitles drawn into the frames, in your browser and without uploading the video. Open the video (MP4, MOV, M4V, WebM or MKV), import an SRT or VTT, set the font, colours and a background box for readability on bright scenes, and render. Rendering needs a computer with Chrome or Edge 94 or later, Safari 16.4 or later, or Firefox 130 or later.

Two details make the result cast more reliably:

• Older Chromecasts list H.264 at up to 1080p and 30 fps. A 60 fps phone video rendered at full rate may not play smoothly on a first or second generation device; the free frame rate tool can bring it down to 30 fps.
• Choose a slightly larger font and a background box than you would for a laptop. Text has to be legible from a sofa across the room, and the editor's safe-area guide keeps it clear of the screen edges that some TVs crop.

What can't be fixed from your side

• SRT straight to the Chromecast. Google's list doesn't include it, so something has to convert it or draw it.
• Subtitle styling beyond the player's defaults. WebVTT cues can carry some formatting, but how a receiver app renders them is up to that app; ASS typesetting doesn't survive either conversion.
• Image-based tracks without transcoding. PGS and VobSub need to be burned in by software that can read them, or replaced with a text version.
• Codec limits of your model. If the Chromecast can't decode the video, subtitles are irrelevant until the video is re-encoded.

Need the subtitles in the first place?

If the video has no subtitle file, the subtitle generator transcribes its speech into SRT or VTT in 100 languages, at 1 credit per minute with a 5-credit minimum per file; a 90-minute film's audio costs 90 credits (9¢). Only the audio track is uploaded for the AI step, and it's deleted within 30 minutes of the job finishing. Download the VTT directly if your casting app wants WebVTT.