Burned-in subtitles are text drawn into the video frames themselves, so there is no caption track left for a player to switch on or off. On X that distinction matters more than it does elsewhere, because two rules in X's own documentation decide whether an uploaded subtitle file is ever shown to a given viewer. This walkthrough covers what those rules say, and how to produce a file whose captions do not depend on them.
You need two things to follow along: the video, and a subtitle file that matches it.
What X's subtitle upload does and does not guarantee
Start with the count. X's Media Studio Library FAQ answers it in one line:
"Can I upload multiple subtitles per video? Currently we only support one subtitle file uploaded per video."
One file means one language track. The same FAQ then explains when that track is drawn:
"When a video with subtitles is viewed on X, the subtitles will appear as an overlay atop the video when the subtitles language matches the language set on the viewing user's device (on desktop, the subtitles language is matched to the user's X language settings). If the subtitles language is not the same as the language of the user, subtitles will not appear."
Read those two answers together and the consequence is concrete: you get one language, and anyone whose device or X language setting differs from it sees no subtitles at all. Not smaller subtitles, not untranslated subtitles — none. There is no signal on the posting side telling you how many people fall into that group.
Even for viewers whose language does match, the track is conditional:
"By default, subtitles appear when the video's sound is not playing, and will be hidden when sound is playing. Some users may have subtitles enabled within their device's accessibility settings—if this is the case, then subtitles will always show, regardless of whether audio is on or if full-screen view is in use."
Keep the scope straight, because this is the part most write-ups drop. Those answers come from the Media Studio Library page, and that page draws its own boundary at the top of its specifications: "These instructions are only valid for Media Studio, and should not be followed for usage of the X developer API, Pro Media API, desktop upload, or mobile upload." Whether the ordinary web caption upload behaves identically is not something X's help center states — check the official documentation rather than assuming.
What the caption upload page does state is where the feature lives at all:
"Note: Currently this feature is available on web only."
Burned-in text is unaffected by every one of those conditions, for the simple reason that no subtitle file is involved. There is no language to match, no track to toggle, no per-video limit of one, and no web-only upload step.
Before you start
- A video file. If yours is a QuickTime
.mov, note that Media Studio's own troubleshooting says of processing problems: "This happens most often with .mov files. If possible, re-export files as .mp4, which should allow for overall faster upload and processing time." MOV to MP4 handles that conversion in the browser. - A subtitle file that lines up with the video. If you also intend to upload the sidecar file separately, X lists four format checks for SRT — chronology, spaces, timestamps and digits — and the error it throws when one fails: "There was a problem uploading your subtitle (.srt) file". The help-center pages on captions discuss
.srtonly; the API'smedia_typeenumeration separately lists bothtext/srtandtext/vtt. If you are holding a WebVTT file, SRT to VTT converts in either direction. - Nothing installed. Burning in is a re-encode of the picture, which the browser tool below does locally.
Step 1: Check the subtitle timings against the video
Play the video and confirm the first cue lands where the speech starts. Burning is a one-way operation on the picture, so an offset you did not catch is baked in and only fixable by redoing the burn.
Step 2: Burn the subtitles into the frames
Load the video and the subtitle file, and export. The result is a normal video file with the words rendered into every frame.
Try it right here
Runs in your browser. Your file is not uploaded anywhere.
Both files are read from your disk and processed in the browser tab — nothing is uploaded to a server, which matters for unreleased footage. The same tool has a standalone page at burn subtitles to video.
Step 3: Sanity-check the export before posting
X's developer documentation lists hard requirements for video it ingests, and they are worth checking against whatever your editor produced, because none of them are about file size. Verbatim: pixel format — "Only YUV 4:2:0 is supported"; audio "must be AAC with Low Complexity profile. (High-Efficiency AAC is not supported)"; audio "must be mono or stereo, not 5.1 or greater"; the file "Must not have open GOP" and "Must use progressive scan". The recommended video codec on that same page is H264 High Profile, with AAC LC audio.
Two things X says about what happens after you post are also worth knowing before you judge the result. On quality, X's page about longer videos states: "we may modify or adapt your original video for distribution, syndication, publication, or broadcast by us and our partners and/or make changes in order to adapt it to different media, including modifying the resolution and bitrate of the original video while streaming based on the speed and stability of the viewer's internet connection." And on playback resolution, the developer docs say: "Subscribed users can upload a 1080p video and get 1080p playback. Unsubscribed users can upload a 720p video and get a 720p playback."
Burned-in captions ride through that processing as picture, so legibility is a function of how the video is re-encoded. Larger type survives a bitrate drop better than small type does.
Common mistakes
- Assuming a subtitle file you uploaded is visible because you can see it. Media Studio's FAQ is explicit that a matching language is what triggers the overlay, and that mismatched viewers get nothing.
- Testing in the Media Studio preview player. Its FAQ answers this directly: "I uploaded a subtitle, why doesn't appear in the preview player in Media Studio? Correct. Subtitle files will only be shown once posted."
- Expecting the caption upload flow on a phone. X's caption upload page says the feature is "available on web only."
- Applying Media Studio's rules everywhere. That page disclaims desktop upload, mobile upload and the API by name. Access is also gated: X states "Access to Media Studio will be given to verified subscribers only," and that it "is not available to Basic tier subscribers."
- Burning before the timings are right. Fix the sync first; there is no undo inside the pixels.
FAQ
Can I upload more than one subtitle file to an X video? X's Media Studio Library FAQ says: "Currently we only support one subtitle file uploaded per video." If you need more than one language visible, burning the text into the picture is the path that does not depend on that count.
Why don't my subtitles show up on X even though I uploaded them? The documented condition is language. Subtitles appear "when the subtitles language matches the language set on the viewing user's device," and X states that if the languages differ, "subtitles will not appear." Note that this answer is on the Media Studio page, which scopes itself away from desktop, mobile and API uploads.
Can I add captions to an X video from my phone? X's page on uploading a caption file says the feature is "available on web only." Burning the captions in beforehand produces a single video file with nothing left to attach, so the upload itself is an ordinary video post.
Does burning subtitles in reduce video quality? It re-encodes the picture, and X separately says it "may modify or adapt your original video," including "modifying the resolution and bitrate." Export at a sensible bitrate and keep the caption type large enough to survive that.
Is there a size limit on subtitle files?
The API's media category table lists a 1 MB maximum for the subtitles category. That figure is from the developer documentation, not the help center — for the web upload path, check the official documentation.
Browser-side conversion and subtitle tools are collected at all Clapr tools, and more step-by-step guides live in the how-to section. For X's numeric caps, see X video file size limits.
All quotations are from X's help center and developer documentation, checked 16 September 2026. X has published differing figures on different pages before — verify against the official pages before relying on them.
