How to Add Subtitles in Avidemux (SRT & ASS Guide)

Avidemux burns subtitles directly into the video picture (hardsub) through its SSA/ASS subtitle filter. You cannot mux a soft-subtitle stream — SRT files must first be converted to SSA/ASS format. Once burned in, subtitles become part of the image itself, so they show on every player and device.

Heads-up: hardsubbing is irreversible. The original pixels are replaced permanently, so always keep a backup of the source file before you start.

Before You Start: Convert SRT to ASS

Avidemux’s subtitle filter loads .ass / .ssa files. If your subtitles are in .srt format, convert them first:

  • Subtitle Edit (free, Windows): open the SRT, choose Save as → Advanced Sub Station Alpha (.ass).
  • Aegisub (free): open the SRT and save directly as ASS — also handy for restyling fonts and colors.
  • Online converters: fine for quick jobs, but avoid them for files you care about privacy-wise.

Avidemux does not convert SRT to SSA/ASS internally, so this step cannot be skipped.

Step-by-Step: Burn Subtitles into Your Video

  1. Load your video. Open Avidemux and drag the video file into the window. The Video Output must be set to a re-encoding encoder (e.g. Mpeg4 AVC (x264)) — not Copy — because the filter can only be applied when the video is re-encoded. See how Copy mode works if you need lossless trimming instead.
  2. Open the filter manager. Go to Video → Filters. In the filter list on the left, scroll to the Subtitles category and select SSA/ASS, then click the green plus button to add it to the active filter chain.
  3. Load the subtitle file. In the SSA filter dialog, click the browse button and select your .ass file. A preview with the subtitles rendered appears on the right side of the dialog.
  4. Adjust font, style, and position. The dialog lets you change the font, size, primary color, outline, and vertical position. Pick a widely available font (see the note below) and check the preview at a few timestamps — especially the bottom lines where the safe-area matters.
  5. Set the output and encode. Keep Audio Output on your preferred encoder (AAC is a safe default) and Output Format on MP4 or MKV. Save with File → Save (or Ctrl+S) and wait for the encode to finish. Subtitles are baked into the picture of the new file.
Font tip: if the player on the target device is missing the font embedded in the ASS file, you may get boxes or garbled glyphs. Stick to common fonts (Arial, DejaVu Sans, Noto Sans) — particularly important for CJK subtitles, where missing font support shows as empty boxes.

Common Problems

Symptom Likely cause Fix
Subtitle file loads but nothing shows File is still SRT, or timestamps don’t match the video’s frame rate Convert to ASS; check that the ASS timing matches the video
Boxes or gibberish instead of text Missing font, wrong encoding Set a font that exists on your system and save the ASS as UTF-8
Filter list shows no SSA entry Very old Avidemux build Download Avidemux 2.8.1, the current stable release

FAQ

Can I use an SRT file directly in Avidemux?

No. Avidemux’s subtitle filter only reads SSA/ASS. Convert the SRT with Subtitle Edit or Aegisub first — it takes under a minute and also lets you fix styling.

My subtitles are out of sync. What do I do?

Fix the timing in the subtitle file before loading it into Avidemux. Subtitle Edit can shift all timings by a constant offset or resync to the audio waveform; Avidemux itself has no subtitle timing adjustment.

Can Avidemux add soft subtitles (a toggleable subtitle track)?

No — Avidemux only burns subtitles into the picture. If you want a separate, switchable subtitle stream, mux the video and SRT together into an MKV with MKVToolNix instead; that keeps the video untouched.

Why do my Chinese / Japanese / Korean subtitles show as boxes?

The font chosen in the ASS style is not installed (or the file is not UTF-8). Set the style font to a CJK-capable font such as Noto Sans CJK, save the ASS as UTF-8, and the glyphs will render correctly.