VIDEO + SUBTITLE FILE → VIDEO WITH SUBTITLES

Add subtitles to video.

1. Choose a video

MP4 input. Video and audio stay on your device.

2. Choose subtitles

One SRT or WebVTT file with real cue timing.

Switchable subtitle track

Keep the original video and audio streams. Put a selectable text subtitle track in an MP4 or MKV file. The text track is converted to the container's subtitle format.

Output container

Visible burn-in

Draw subtitles onto every affected frame. Video must be encoded again; lossless H.264 mode keeps the input frame size and rate but can produce a much larger file. The text cannot be switched off.

Choose one video and one subtitle file, then choose an output mode.

Everything runs in your browser. Your video and subtitle files are never uploaded; the FFmpeg runtime is downloaded to your browser.

Output differences

Tested input: MP4 with H.264 video, 8-bit yuv420p pixels and AAC audio. The track option copies the original picture and sound streams without re-encoding. MP4 output uses a selectable mov_text subtitle track; MKV output uses a selectable SRT track. Your player must support the chosen track. Burn-in is available for the tested H.264/yuv420p input; it draws text with a local font, encodes lossless H.264 video at the original dimensions and frame rate, and copies the audio. Its MP4 file may grow substantially.

Measured on this Windows test machine

Sample	MP4 track	MKV track	Visible burn-in
15 s · 320×180 · 2 fps	<0.1 s	0.1 s	0.2 s
75 s · 640×360 · 24 fps	0.3 s	0.2 s	13.0 s, 20 cues

These are measured processing times with the runtime already loaded in the browser; the first runtime download takes additional time. The 75-second test input was 6.61 MiB and its 20-cue lossless burn-in output was 43.74 MiB. The burned test kept its original resolution and frame rate, and sampled picture regions without subtitles matched the input pixels. Longer clips, other codecs, or larger files are untested here and may exceed browser memory. There is no fixed file-length promise.

Burn-in progress and remaining-time estimates use encoded video time and can change as encoding speed changes. Check the downloaded video and subtitle timing before using it.

Need to make a subtitle file first? Use auto captions for audio or video, VTT to SRT, SRT to VTT, Text to SRT, SRT to TXT, VTT to TXT, the subtitle converter, ASS to SRT, SUP to SRT, the CPS checker, subtitle editor, or video to text for paragraph text.

Extract tracks from an MKV