Add Subtitles to Video (Burn In SRT, VTT or ASS)

About the Add Subtitles to Video (Burn In SRT, VTT or ASS)

Choose a video and its subtitles — an SRT, WebVTT, ASS/SSA, SBV, TTML, MicroDVD or LRC file, subtitles you paste, or the text subtitles inside an MKV — and this page adds them in one of two ways. Burned in, the words become part of the picture: they show on every phone, app and site, in the style you choose — font, size, colour, an outline or a box, the position and the distance from the edge — and an ASS file keeps its own fonts, colours and positions. As a subtitle track, they are stored next to the picture in an MP4 or MKV file, so viewers switch them on and off and choose the language; nothing is re-encoded, so even a film takes only moments.

The preview plays your video with the subtitles drawn over it exactly as they will be burned in, and a readability check against the Netflix guide marks lines that are too long, too fast to read or too short on screen. Everything runs on your device: the video and the subtitles are not uploaded.

The free preview on this page is up to 10 seconds of the result (half of a shorter video), from where the subtitles start, at the settings you chose, with a MySmartCoPilot watermark. With a Pro pass, or after unlocking this one video, you get the whole video.

Burned in or a subtitle track?

Burned-in subtitles (also called hard subtitles or open captions) are drawn into every frame, so they show wherever the video plays — in messaging apps, on social sites and on TVs that ignore subtitle tracks — but they cannot be switched off, and the picture is re-encoded, which takes a while for a long video. A subtitle track (soft subtitles) is stored beside the picture: viewers switch it on and off, several languages can share one file, and the picture and sound are copied untouched in seconds. In an MP4 the tracks are 3GPP timed text, the MP4 subtitle format that QuickTime, iPhones and iPads list in their subtitles menu, as do VLC and players built on FFmpeg; in an MKV they are SubRip text, which MKV players read. Messaging apps and social sites ignore subtitle tracks. For YouTube, you can also upload the subtitle file itself in YouTube Studio (Subtitles → Add language → Upload file), where viewers switch it on and off.

A readable style

The styles follow the Netflix Timed Text Style Guide: white text, centred, at the bottom or the top, at most two lines, and a size that fits about 42 characters across the screen (English guide). The size is set as a share of the picture’s shorter side, so a portrait reel and a landscape film get the same text size. Text stays at least 5% in from the sides — the graphics-safe area of EBU R 95 — and you set how far it sits from the top or bottom edge: raise it on phone videos, where apps draw their buttons and captions over the bottom of the picture (Meta’s Reels guide suggests keeping the lowest 35% clear of text). A line too long for the width is broken into lines of even length, the bottom one the longer, after punctuation where that costs little. An outline, a shadow or a box keeps text readable on any picture; the page warns when a style has none of them, or when the text and box colours are too close (less than the 4.5:1 contrast WCAG asks for).

What is kept from the subtitle file

• SRT, WebVTT and the other formats: bold, italic, underline, strike-through and colours (untick Keep the file’s bold, italic and colours to draw everything in your style), and lines the file puts at the top or to one side — such as {\an8} in SRT or line:10% in WebVTT — stay there. Line breaks are kept as the file has them.
• ASS and SSA, with Use the file’s own ASS styles: the script’s resolution, styles, fonts, sizes, colours and transparency, bold, italic, underline, scaling, spacing, outlines, shadows and opaque boxes, the nine alignments and margins, \pos, \move, \org with \frz, and \fad fades (override tags, ASS File Format Guide). Animated tags (\t), karaoke timing, vector drawings, clipping, 3D rotation and blur are not drawn, and the page lists the lines that use them. A font named in the file is used when this device has it; otherwise Noto Sans stands in.
• Subtitle tracks: in MP4, bold, italic and underline are kept (3GPP timed text has no placement that players agree on, so lines show at the bottom); in MKV, bold, italic, underline, colours and lines at the top or a side are kept as SubRip tags ({\an8}). Fonts are left to the player. WebVTT cue settings are read as the W3C WebVTT format defines them.

Fonts and languages

The bundled fonts — Noto Sans, Montserrat, Poppins, Anton and Bebas Neue, under the SIL Open Font License — load from this site, only for the letters your subtitles use. Noto Sans covers Latin, Greek, Cyrillic, Vietnamese and Devanagari (Hindi, Marathi, Nepali); Bengali, Tamil, Telugu, Gujarati, Gurmukhi, Kannada, Malayalam, Odia, Arabic, Hebrew, Thai, Chinese, Japanese and Korean are drawn with the fonts of your device, and lines in scripts without spaces are broken between words. Each track gets its language code (ISO 639-2), so players name it in their menu. The readability check uses the Netflix limits for the language: 20 characters a second for English, 22 for Hindi and the other Indian languages Netflix lists, 17 for most others.

The video file

Burned in, the video is an MP4 with H.264 (or a WebM with VP9) at the size of the original or a smaller one you choose, at the original’s bitrate scaled to that size, with the sound copied as it is where the format allows. As a track, the picture and sound are copied without re-encoding into MKV (any codec) or MP4 (H.264, HEVC, AV1 or VP9 with AAC, MP3, Opus or Dolby Digital); a codec MP4 cannot hold is re-encoded, and the page says so before anything runs. Phone videos come out upright. Chrome and Edge on a computer can write a long video straight into a file while it is made.

Limitations

• Burning subtitles in re-encodes the video: a long film takes a while, and a phone may run out of memory with one — use a computer, a smaller size, or add the subtitles as a track instead.
• Picture subtitles (Blu-ray PGS, DVD VobSub) are images, not text: they need OCR first.
• Subtitle tracks already inside the video are not copied into the new file; add the ones you want back from Subtitles inside this video (MKV and WebM files).
• Subtitle tracks show only in players that offer subtitles; messaging apps and social sites ignore them, so burn the subtitles in for those.
• An ASS script’s animated effects, karaoke timing, drawings, clipping, 3D rotation and blur are not drawn.

Privacy

Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot.