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Supported Formats

Video Formats

AutoSubtitles supports most common video formats, including:

  • MP4 (.mp4) — The most widely used video format
  • MOV (.mov) — Common on Apple devices
  • WebM (.webm) — Web-optimized format
  • AVI (.avi)
  • MKV (.mkv)

Your video is processed entirely in your browser using your device's built-in media capabilities. If your browser can play the video, AutoSubtitles can work with it.

A note on HEVC / H.265

HEVC (H.265) is the codec used by iPhones for high-quality recording and by many 4K cameras. Because HEVC is patent-encumbered, fast in-browser decoders for it aren't available on every browser:

  • Chrome / Edge — Full speed and full source framerate (including 4K 60fps) via the system HEVC decoder. Recommended browser for HEVC footage.
  • Safari — Uses macOS/iOS native HEVC hardware decoding. Exports at full framerate.
  • Firefox — Works, but Firefox's internal throttling of offscreen video can lower the output framerate. If you're exporting HEVC on Firefox and need to preserve framerate exactly, use Chrome or Edge instead.

H.264 / AVC, VP9, and AV1 footage is decoded at full speed on all supported browsers and is not affected.

Audio Formats

For transcription, AutoSubtitles extracts the audio track from your video. The AI transcription service supports all common audio codecs.

When you export a subtitled video, the original audio from your video is reused. AutoSubtitles does not change the audio codec, sample rate, or other audio settings.

Subtitle Export Formats

AutoSubtitles can export subtitles in the following formats:

  • Burned-in video — Subtitles rendered directly into the video file, also called open captions (open vs closed captions). No separate subtitle file needed. Available on every plan.
  • SRT (.srt) — The most widely supported subtitle format (what an SRT file is and how to use one). Compatible with YouTube, Vimeo, most video players, and most video editors. Pro.
  • VTT (.vtt) — WebVTT format, commonly used for web video players and HTML5 video. Pro.
  • TXT (.txt) — A plain transcript with no timings. Pro.

Already have a subtitle file in the wrong format? The free subtitle converter turns SRT into VTT, VTT into SRT, and either into plain text, right in your browser. To fix words or timings in an SRT or VTT file, use the free subtitle editor. If a file is out of sync with its video, the subtitle shifter moves every subtitle earlier or later.

File Size

There's no strict file size limit, but very large files may take longer to process depending on your device's memory and processing power. For the best experience, we recommend videos under 500MB.

Aspect Ratios

AutoSubtitles works with any aspect ratio:

  • 16:9 — Standard landscape (YouTube)
  • 9:16 — Vertical/portrait (Instagram Reels, TikTok, YouTube Shorts)
  • 1:1 — Square (Instagram feed)
  • 4:3 — Classic TV format
  • Any custom aspect ratio