Convert Subtitles to SRT: Every Format Explained (2026)
Convert Subtitles to SRT: Every Format Explained (2026)
Subtitle files were supposed to be simple. Then you downloaded a .sup, a .sub came with a mysterious .idx beside it, YouTube handed you a .vtt, and a fan group delivered an .ass file full of rainbow-colored karaoke effects — and nothing plays them all. Welcome to the reason converting subtitles to SRT is one of the most-searched subtitle tasks on the internet.
This guide covers every mainstream subtitle format, what each one is actually for, which devices accept them, and exactly how to convert anything into (or out of) SRT with free online tools — OCR-based image conversion included. By the end, you'll be able to look at any odd file extension and know in one second: convert it, rename it, or leave it alone.
Table of contents
Why SRT is the format everything else gets compared to
All subtitle formats, decoded (SRT, VTT, SSA/ASS, SUB/IDX, SUP/PGS, TTML/DFXP, SBV, and more)
Which players accept which formats (compatibility table)
Text vs. image subtitles — the divide that causes 90% of problems
How to convert SUB/IDX to SRT (OCR guide)
How to convert SUP/PGS to SRT (OCR guide)
SRT to VTT, plain text, PDF, and other conversions
Fixing timing while you're at it: FPS, merge, split and offset conversions
Common conversion mistakes (and how to avoid OCR errors)
FAQ
Full honesty: SRT is technically the simplest subtitle format in existence, and that's exactly why it wins.
The file is plain text with numbered blocks:
42
00:00:31,200 --> 00:00:34,100
We should talk about the letter.
43
00:00:34,500 --> 00:00:37,000
What letter?
No XML, no binary container, no color data, no styling. Just counter, timestamps, text. It was invented in 2000 by a Russian student who wrote a tool that extracted subtitles from DVDs, and twenty-five years later it's still the lingua franca of subtitling:
Every serious player reads it — VLC, Plex, Kodi, Jellyfin, Infuse, MX Player, Windows Media Player-class tools, every smart TV, Roku, Fire TV, Android TV, iOS, Premiere Pro, CapCut, DaVinci Resolve, ffmpeg, YouTube.
It's human-editable in any text editor.
It's tiny — a 2-hour movie is typically under 200 KB.
It never fails on encoding if it's saved as UTF-8.
What SRT can't do: colors, fonts, positioning, animated effects, and it can't exist as an image. Those needs are exactly what the other formats exist for. So the universal rule of subtitle formats is:
Keep your subtitle library in SRT. Convert anything else the moment you can, and go back up to a fancier format only if you have a specific reason.
That's why every guide on this topic is written "to SRT" and not the other way around.
[IMAGE: A diagram showing one central "SRT" box with arrows incoming from SUP, SUB/IDX, VTT, ASS, SBV, TTML and outgoing to players, TVs, and editors]
Here's every format you're realistically going to meet, what it is, and who it's for.
Plain text, minimal timing, dialogue only. Universal. Weaknesses: no styling, no positioning beyond a basic vertical tweak, no metadata.
The format HTML5 video players use (<track> element). Structurally SRT's cousin with these differences: seconds use a . instead of , for milliseconds, blocks start with WEBVTT, and it supports limited styling (colors, positioning) via CSS-like cues. Browsers, YouTube (in its caption APIs), and many web apps speak it natively; desktop players accept it too but prefer SRT.
Text-based but with a full scripting engine: fonts, colors, gradients, on-screen positions, karaoke timing, rotation, animation. If a fan group's subtitle contains stylistic flourishes, it's ASS. Desktop players like VLC, MPC-HC and MPV render it fully; hardware players, smart TVs and most media servers either ignore the styles or reject the file entirely. This is why anime fans keep ASS for desktop viewing and convert a plain track to SRT for TV.
The classic DVD subtitle: .idx is the index (timings + metadata) and .sub is the binary data — and here's the crucial part: the .sub payload is images, not text. DVDs rendered subtitles graphically, so there is no text to extract without OCR. This pair is why people search "sub to srt" and end up with converts that look like cryptographic tuning guides. More in section 5.
Presentable Graphic Subtitles (PGS) stored in .sup files: same idea, newer standard. Subtitles are full-color images rendered by the disc author. A .sup file has no text inside it at all — extracting dialogue means running OCR over the images. Extremely common in Blu-ray remuxes for European releases and Asia-Pacific discs, which is exactly why "SUP to SRT" is such a popular conversion.
An XML standard used by broadcasters and streaming services (Netflix-style distribution). Very capable, very formal, machine-friendly and messy for humans. Typically used within pipelines; users converting TTML usually want SRT out of it for editing.
A simple format YouTube historically exported captions in. Treated easily as SRT-with-different-commas in conversions.
Broadcast closed captions embedded line-by-line in TV/video streams, mostly invisible in consumer files these days, but if it enters your world (e.g., legacy archival footage), convert it to SRT for anything modern.
Summary table
Format
Type
Styling
Common source
Honey Badger rating (compatibility)
SRT
text
none
everywhere
★★★★★ universal
VTT
text
limited (CSS)
web/HTML5, YouTube
★★★★☆ everywhere modern
ASS/SSA
text/script
full
anime, fan subs
★★☆☆☆ desktop players only
SUB/IDX
binary image
rendered
DVDs
★★☆☆☆ specific players only
SUP/PGS
binary image
rendered
Blu-rays
★★☆☆☆ needs conversion
TTML/DFXP
XML
rich
broadcast/streaming
★★★☆☆ pipelines
SBV
text
minimal
YouTube legacy
★★★★☆ near-universal
Compatibility in one table — this is the whole reason conversions exist:
Player / platform
SRT
VTT
ASS/SSA
SUB/IDX
SUP
VLC (desktop)
✓
✓
✓ full
✓
✓
Windows Movies / legacy players
✓
partial
✗ mostly
✗
✗
macOS QuickTime
✗ (converted only)
✓
✗
✗
✗
Plex
✓
✓
✓* (styles partial)
✓* (depends)
✗ typically
Jellyfin
✓
✓
✓*
✓*
✗
Kodi
✓
✓
✓ full
✓
✓ via plugin
Roku
✓ (text only)
✗
✗
✗
✗
Fire TV / Android TV
✓
✓ mostly
rarely
rare
✗
Smart TVs (per brand)
✓
mixed
✗
mixed
✗
YouTube (upload)
✓
✓
✗
✗
✗
Premiere Pro / Resolve
✓
✓
import
✗
✗
Browsers (HTML5 )
✗ legacy
✓
✗
✗
✗
The pattern is unmistakable: SRT plays literally everywhere; everything else plays somewhere. However strong a format's features, the moment your video leaves a desktop VLC session — onto a Roku, a Samsung TV, a Chromecast — petty format restrictions arrive. This is precisely why "convert to SRT" dominates the phrase book.
Within all these formats lies a hidden split that even experienced users trip over:
Text-based (SRT, VTT, ASS, SBV, TTML): a file of characters + timings. Machines can read, edit, translate, search, and re-time them. Converting text-to-text is essentially a syntax rewrite — lossless, instant.
Image-based (SUB/IDX, SUP/PGS): a file of pictures timed to appear. No text exists. To convert, a machine must look at each picture, recognize the characters via OCR, and reconstruct dialogue text.
This distinction explains the two most common subtitle mysteries:
Mystery 1: "Why can't my TV see the subtitles inside the MKV?" Your MKV contains a PGS/SUP track from the Blu-ray. Desktop VLC renders those image tracks fine. Roku/Samsung/Chromecast hardware: not so much. The track is "there" but invisible to viewers on the TV. Fix: convert the SUP to SRT, replace the track (or load SRT alongside it).
Mystery 2: "Why is SRT conversion taking longer than a text conversion?" Because it isn't a rewrite — it's OCR. The software renders each timed image and pattern-matches letters. Good converters get ~98%+ accuracy with clean input; sloppy scans of SD Blu-rays produce more errors. See section 9 for the OCR accuracy checklist.
Practical rule of thumb:
If the file's subtitle track came off a DVD or Blu-ray, expect images. If it came from the internet, a streaming export, or a fan translation, expect text.
[IMAGE: Side-by-side comparison: a text subtitle (SRT opened in Notepad) vs. an image subtitle (a rendered SUP frame with big graphic text)]
The DVD-era pair (.sub + .idx) is the single most common image-based format people hold. Two sub-cases and their fixes:
Case A — you have the .sub/.idx pair and want the text for editing/translation. The right conversion is OCR. Steps with a free online converter (drag-and-drop, browser-based, no install):
Go to an online SUB/IDX to SRT converter — e.g., the online subtitle converter suite includes a dedicated SUB IDX → SRT page.
Upload both files: the .idx and the .sub (converters need the timings from the .idx and the images from the .sub).
Pick the OCR language to match the subtitles (English, Spanish, etc.). Wrong language = alphabet soup.
Run convert. Download the resulting .srt.
Open the SRT in a text editor and scan for obviously wrong words — 30 seconds of proofreading is usually enough for a clean disc scan.
Case B — you have a VobSub inside an MKV and want SRT alongside. Extract the pair first (MKVToolNix: open MKV → see tracks → extract the subtitle track), then run Case A on the result. Converting directly from within the container is possible with desktop software, but the extract-then-OCR two-step is simpler and works with free online tools.
Why it works: the converter renders each image against the OCR engine for the chosen language, maps each recognized phrase to its timestamps from the .idx, and writes a fresh SRT. The timing data is preserved exactly — timing fidelity is never a problem in SUB/IDX conversions; only letter-recognition accuracy varies.
[IMAGE: Four-panel strip: upload .sub+.idx → choose language OCR → converting UI → downloaded SRT opened in Notepad]
The Blu-ray child of the DVD image-subtitle family. Same principle, one more step of caution.
Get the SUP file. Three ways it arrives in your hands:
extracted with MKVToolNix from an MKV remux,
provided along a Blu-ray disc image or port (e.g., a `.sup` from a Blu-ray folder),
downloaded as-is from a fan-subtitling source.
Feed the .sup to an online SUP to SRT converter. The SUPTOSRT page in the free subtitle tool suite handles it in-browser: SUP in → choose OCR language → SRT out.
Choose the correct OCR language — SUP images with accented content (é, ü, ç) need a language setting that supports those characters, or they'll come out mangled.
OCR in one click; check the output.
*Scenes where converting SUP is necessary and not optional:*
Blu-ray subtitles your smart TV simply won't render from an MKV.
Building an SRT library for Plex/Jellyfin auto-refreshes (image tracks don't integrate with library subtitle matching).
Translation work — you can't translate an image; you translate text.
Extracting dialogue to plain text for articles, quotes, accessibility notes, or training datasets.
A word of caution on frame rendering: PGS is positioned absolutely on screen (it can fill the whole frame, oversize itself during pans). OCR handles the timing and text extraction, but the visual styling goes away when you move to SRT. If the stylized look matters, you're converting toward loss and knowingly — that's fine, but worth saying out loud.
Text-to-text conversions have no OCR step; they're just syntax rewrites that take seconds.
For HTML5 <track> captions on websites, or platforms that prefer .vtt online. Mechanically: replace comma milliseconds with periods, add a WEBVTT header, optionally keep the SRT cue numbering. Any SRT→VTT online converter does it instantly. Go the other way (VTT→SRT) by stripping the header and flipping punctuation.
Strips timings, keeps only dialogue. Perfect for:
feeding a translation engine (Google/DeepL) to later re-time the translated cues,
producing clean transcripts for essays, notes, and LLM prompts,
accessibility scripts and spoken-word archives.
A "subtitles to text" tool does this in one click, keeping line order per cue.
Subtitle-to-PDF output is a niche but handy formatting choice for scripts, reading-comprehension sheets and printed dialogue scripts — a convert subtitles to PDF page is included in the same free tool suite. Nothing changes technically — it's just the same text, laid out for a printer.
All supported by the same class of converters. Direction between any two text formats is a mechanical transform — the tools handle it via SRT as an intermediate: SBV → SRT, then SRT → VTT, etc. The SRT files are the perfect hub.
Full re-encodes of video (MP4/MKV conversion, embedded-track remuxing, burn-in) are heavy-weight operations — keep them out of browser tabs and inside proper software (ffmpeg, MKVToolNix, Shutter Encoder, etc.). Browsers are for text and image subtitle work.
Since you're in a converter neighborhood, four adjacent tools frequently finish the job:
Frame-rate drift is the number one cause of "my subtitles slide out of sync slowly." If a subtitle was authored at 25 fps and your video is 23.976 fps (or vice versa), a change-subtitle-fps conversion rescales every timestamp by the exact ratio and the drift disappears. Rule of thumb: constant offset = shift; growing offset = FPS change.
Two use cases:
Join two halves of a movie whose subtitles came in CD1 and CD2 files (thrillingly common for older films).
Combine two languages into one file (positioning gets tricky — most tools stack them) — mostly a translations-by-side workflow.
A merge-subtitles-online tool stitches files, renumbers cues, and optionally normalizes overlapping timings.
The inverse: one subtitle file split at a time boundary into two halves — useful when you've split the video into two parts and the SRT must follow. Good tools let you split by timestamp or "after cue #N".
Constant sync offset (the subtitles are 2 seconds early everywhere) is fixed by adding/subtracting the same amount from every timestamp. Most converters offer a shift in the same interface, so you rarely need a separate tool.
These four are all safe to do on any text-based SRT — timing math with no OCR involved.
Fixing your source input prevents 95% of conversion grief:
1. Wrong OCR language. The #1 cause of garbage output. If the subtitles are English, pick English; Spanish pick Spanish — on languages with accented alphabets (French, German, Vietnamese, Turkish), the language setting decides whether é and ü survive.
2. Low-quality sources. OCR can be perfect on a crisp 1080p graphic, marginal on a 480p SD disc scan with compression artifacts. If your source is chewed up badly, expect more errors — either accept a proofreading pass, or cite a better-drawn source (higher resolution Blu-ray over the DVD version, if available).
3. Wrong pairing. SUB/IDX files arrive in pairs; SUP files travel solo. Uploading the .sub without the .idx removes the timing data — the converter can't guess when each cue belongs, so always upload both.
4. Expecting styling to survive. Image formats carry fonts, colors, positions and (occasionally) unique drawn effects. SRT deletes them by design. Only the text and timings survive — that's the point of the conversion.
5. Not proofreading. Even 98% accuracy means roughly one wrong word every 50. Skim your SRT for nonsensical words; fix obvious OCR confusions (rn/m, l/I, O/0) with any text editor. 30-60 seconds saves you the mid-movie double-take.
6. Wasting time converting when copying would do. If your file is already SRT, no conversion is needed — "not displaying" is far more often a naming problem (subtitle file next to video with the same base name) than a format problem. Check naming first; convert second. (That whole naming trick is covered fully in our how-to-add-subtitles guide.)
7. Non-UTF-8 output becomes é. When you save a converted SRT, save it as UTF-8 — every player and platform avoids encoding pain if the file is UTF-8, full stop. If your converted file shows garbled accented letters, this — not OCR — was usually the cause.
Q: What is the universal subtitle format? SRT. It's plain text with timings, readable by every serious player, editor, and platform. Everything else is either an enhancement (ASS styling, VTT web features) or a container-era legacy (SUB/IDX, SUP/PGS images from DVDs and Blu-rays).
Q: How do I convert a .sup file to SRT? With an OCR converter: upload the .sup, choose the subtitle language, run, download the SRT. Since SUP is image-based, there is no text inside it to extract — the converter reads the characters out of the images. Try the dedicated SUP to SRT page in the free tool suite.
Q: How do I convert SUB/IDX to SRT? Upload both files (the .idx holds timings; the .sub holds images) to an online converter, pick OCR language, run, download SRT, and skim the result for OCR typos.
Q: Can I merge two subtitle files into one? Yes — a merge tool joins files by renumbering cues and shifting the second file's timings to follow the first. Designed for CD1/CD2-style movie subtitle pairs, but works on any two text SRTs.
Q: My subtitles slowly drift out of sync — what do I do? Growing drift indicates a frame-rate mismatch. Convert the subtitle with an FPS-change tool (usually 23.976 ↔ 25 fps). A constant offset, by contrast, is a plain shift fix.
Q: Why won't my smart TV play the subtitles inside my MKV? Likely an image-based track (PGS/SUP). Desktop VLC renders it; TVs and streaming boxes often won't. Convert the SUP/SUB track to SRT, then load the SRT alongside your video.
Q: Is converting a subtitle file legal? Convert a file you already possess — yes. Format conversion is a transformation, not distribution. The question of the content's rights (dialogue, manga scans) is separate but not affected by the act of converting.
Q: VTT vs SRT — which should I choose? SRT for anything player/desktop/TV-related (universality). VTT for browser-embedded HTML5 video or web apps that demand it. Users keep master copies in SRT and convert to VTT on demand.
Q: Do conversions lose timing accuracy? Text-to-text conversions preserve the timing exactly (measured to the millisecond). Image-to-text (OCR) conversions preserve timing exactly too — but add the risk of misread characters. Proofread the result.
Q: What tool do I use for burning subtitles into a video? That's video editing — beyond online subtitle converters. Use an editor (Premiere/CapCut/DaVinci), or a one-line ffmpeg with the subtitles filter if you know the command line.
Here's the one-paragraph version of everything you've read:
SRT is the hub. DVD-era SUB/IDX and Blu-ray SUP tracks are images and need OCR conversion with the right language setting. VTT, SBV and TTML are just SRT's cousins you convert through the hub for the web. Frame-rate drift, constant offsets, splits and merges are all just timestamp math that online tools fix in a click. Your best habit is building everything around SRT — text-based, UTF-8, matched files — because it's the format every player, editor and platform on earth accepts without an argument.
Whether you keep the tool suite open for sup → SRT rescues on movie night or use it once a year for a YouTube caption pull, a good online subtitle converter turns the format zoo from a barrier into a footnote. Every subtitle file — regardless of the cryptic three-letter extension it arrives with — becomes an ordinary, editable, universal SRT in under a minute. That's the entire game.