What is the difference between SRT, VTT, and ASS subtitles?

SRT is the universal plain-text format: timestamps plus lines, no styling, plays everywhere. VTT is the web-native sibling: same idea plus positioning, styling, and chapters — required for HTML5 video. ASS adds full karaoke-grade styling (fonts, colors, positions, effects) for fansubs and stylized anime — powerful but supported by fewer players.

Should I burn subtitles in or keep them as soft subs?

Burn in (hardcode) when compatibility is everything: TikTok, Reels, Shorts, client previews, subtitled screen recordings — the text becomes pixels, so it shows on every screen ever made. Keep soft (separate selectable tracks) for Plex libraries, YouTube uploads, and archival, where viewers toggle languages and styling.

How do I burn SRT subtitles into a video with FFmpeg?

Use the subtitles filter: 'ffmpeg -i in.mp4 -vf subtitles=subs.srt out.mp4'. Style inline with force_style (e.g. FontName, FontSize, PrimaryColour). This re-encodes the video — add '-c:v libx264 -crf 20 -c:a copy' to control quality explicitly and skip re-encoding the audio.

Why aren't my subtitles showing in Plex or on TV?

Usually image subtitles (PGS/VOBSUB) on a client that can't overlay them, or an ASS file with fonts the client lacks. Convert to plain SRT — OCR image subs first if needed — and they direct-play almost everywhere. See our Plex format guide for the full subtitle trap breakdown.

How do I fix out-of-sync subtitles?

For a constant offset, shift the subtitle stream: '-itsoffset 2.5 -i subs.srt' delays subs 2.5s (negative advances). For drift that grows over time, the sub file likely matches a different framerate cut — re-time with Subtitle Edit's point-sync rather than guessing offsets.

Why do my subtitles show gibberish characters?

Character encoding mismatch: the .srt is saved in a legacy codepage (e.g. Windows-1256 for Arabic, Big5 for Traditional Chinese) but read as UTF-8. Re-save the file as UTF-8 (any text editor or Subtitle Edit does this) and the glyphs resolve. Always author and store subtitles as UTF-8.

How do I extract subtitles from an MKV file?

Map the subtitle stream out: 'ffmpeg -i movie.mkv -map 0:s:0 subs.srt' grabs the first subtitle track. List tracks first with 'ffmpeg -i movie.mkv' (no output) to pick the right language index. Text subs extract perfectly; image subs (PGS) extract as .sup needing OCR.

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Subtitles Explained: SRT vs VTT vs ASS (+ How to Burn Them In)

Three text formats, one image-format trap, and the burn-vs-softcode decision that determines whether anyone ever sees your captions. Formats compared, exact commands, and the fixes for sync, gibberish, and invisible subs.

By Hadi Karaki, maker of Formatif: media processing suiteSeptember 16, 202610 min read

SRT vs VTT vs ASS: the one table you need

	SRT	VTT	ASS/SSA
Styling	None (plain text)	Position, color, chapters	Full: fonts, karaoke, effects
Plays on	Everything	Web + most players	VLC, MPV, anime players; patchy on TVs
Best for	Universal subs, Plex, uploads	HTML5 video, web players	Fansubs, styled captions
Plex direct-play	Yes	Mostly	Often forces transcode

Default rule: author in SRT unless you need web chapters (VTT) or heavy styling (ASS) — SRT converts cleanly into both, while the reverse loses formatting. And remember the fourth category: image subs (PGS/VOBSUB) are pictures, not text — the Plex-buffering culprits from our Plex guide.

Burn in or keep soft? Decide by destination

Burn in (hardcode) when…

TikTok, Reels, Shorts — no player sub support to rely on
Client previews and screen recordings — zero failure modes
Styling must survive (ASS effects become pixels)

Keep soft when…

Plex/Jellyfin libraries — viewers toggle languages
YouTube uploads — platform renders and translates
Archival — restyle or re-time later without re-encoding

Quick Solution

Whole season to caption? Skip the per-file commands.

The commands below work — twelve episodes × three commands each is where evenings go. Formatif Pro ($8.95 one-time) batch-burns subtitle tracks across folders offline — file or embedded subs, adjustable font size, same recipe every file — and extracts embedded tracks to SRT/VTT/ASS when you need the text instead.

Download free trial

Burn-in commands (FFmpeg)

Burn SRT in, keep audio untouched

ffmpeg -i in.mp4 -vf subtitles=subs.srt -c:v libx264 -crf 20 -c:a copy out.mp4

Burn with styling

ffmpeg -i in.mp4 -vf "subtitles=subs.ass:force_style='FontName=Arial,FontSize=20,PrimaryColour=&HFFFFFF&,Outline=1'" -c:v libx264 -crf 20 -c:a copy out.mp4

Shift out-of-sync subs by +2.5s

ffmpeg -itsoffset 2.5 -i subs.srt -i in.mp4 -c copy -map 0:s -map 1:v -map 1:a out.mkv

Extract first sub track from MKV

ffmpeg -i movie.mkv -map 0:s:0 subs.srt

Two gotchas: burning re-encodes video (set CRF explicitly — filter-only commands silently pick defaults), and gibberish glyphs mean a legacy codepage file — re-save as UTF-8 before anything else. Growing drift (not constant offset) means a framerate-mismatched sub file: fix with Subtitle Edit's point-sync, not offset guessing.

Subtitle questions, answered

SRT vs VTT vs ASS?

SRT: universal plain text. VTT: web-native with styling/chapters. ASS: full karaoke-grade styling, patchier support. Default SRT.

Burn in or keep soft?

Burn for TikTok/Reels/previews (zero failure modes). Soft for Plex, YouTube, archives (toggleable, restyleable).

FFmpeg burn-in command?

-vf subtitles=subs.srt with explicit -c:v libx264 -crf 20 -c:a copy. Style via force_style; burns require re-encode.

Subs not showing on Plex/TV?

Usually PGS/VOBSUB image subs or font-less ASS. Convert/OCR to SRT — direct-plays almost everywhere.

Fix out-of-sync subs?

Constant offset: -itsoffset shift. Growing drift: framerate-mismatched file — point-sync in Subtitle Edit.

Gibberish characters in subs?

Legacy codepage read as UTF-8. Re-save the .srt as UTF-8. Author everything UTF-8 from the start.

Extract subs from MKV?

ffmpeg -i movie.mkv -map 0:s:0 subs.srt. List tracks first to pick the language; PGS extracts need OCR.

Keep learning

Plex & Jellyfin formats

Where subtitle choices force transcoding — the full trap guide.

Convert MKV to MP4

Extract, convert, and carry subtitle tracks — commands included.

MKV vs MP4 explained

Why MKV carries subtitles best — tracks, chapters, attachments.

Every episode captioned, one run.

Formatif Pro ($8.95 one-time) and Formatif AI ($12.95 one-time) handle video, image, and audio conversion offline — with batch workflows, no file size limits, and a 3-day free trial.

Download free trial Read: Plex format guide

The FFmpeg commands above are complete and free forever — pick whichever method fits your episode count.

Written by

Hadi KarakiLinkedIn

Founder of Formatif, a local-first offline media processing suite for Windows and Linux. Hadi writes about video, image, and audio formats, compression, and privacy-first desktop workflows.