Do these 3 things before closing this tab:
1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsFix FFmpeg subtitle problems by identifying which layer is failing: subtitle stream selection, text encoding, font discovery, ASS styling, or script shaping. For garbled text in a known non-UTF-8 subtitle, set the correct charenc value; for substituted fonts, make the intended font available to the environment running FFmpeg. Those fixes are not interchangeable. The commands and options below apply to FFmpeg builds with the subtitles filter; check your installed version and filter help because build capabilities can vary.
Start by identifying the subtitle and FFmpeg build
Before changing options, note the subtitle file or embedded track, its format, your operating system, the exact command and full error. Run ffmpeg -version to record the version and build configuration. Check that the binary includes the subtitles filter and its relevant options; this filter uses libass to render subtitles, and available capabilities can differ by build.
Determine whether the subtitle is a sidecar file such as .srt or .ass, or a stream inside a video container. Also identify whether the track contains text or images. FFmpeg’s current subtitles-filter implementation rejects a selected non-text subtitle stream, so a bitmap-based track needs a different workflow if your goal is to burn text using this filter.
Choose the intended subtitle track
A container may contain multiple subtitle tracks. Inspect its streams with ffprobe, identify the intended track, and select it explicitly rather than relying on automatic selection. FFmpeg’s filter supports stream_index and its alias si for this purpose. Automatic subtitle selection can depend on the output format and subtitle stream type.
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For a sidecar subtitle, point the filter at that file instead of selecting an embedded track. In either case, verify that the source is text-based before troubleshooting character encoding or fonts.
Fix garbled characters by confirming the encoding
charenc tells the subtitles filter how to decode subtitle input text; it does not install fonts or correct subtitle styling. If the file is UTF-8, leave out a guessed legacy encoding. If you have established that it uses a different encoding, pass that encoding to charenc:
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ffmpeg -i input.mp4 -vf "subtitles=filename=subtitles.srt:charenc=CP1250" -c:a copy output.mp4CP1250 is only an example, not a general recommendation. Use the actual encoding of your subtitle file. A wrong value can leave characters garbled or make them worse. The subtitles filter’s charenc option is passed to the subtitle decoder as its input character encoding.
Fix a missing or substituted font
For ASS/SSA subtitles, check the font family specified by the subtitle style. That font must be discoverable by the environment running FFmpeg—not merely installed on another computer or on the host outside a container. Install or expose the font in that environment, or provide an additional font directory with fontsdir where the option is available:
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ffmpeg -i input.mkv -vf "subtitles=filename=subtitles.ass:fontsdir=/path/to/fonts" -c:a copy output.mp4MKV attachments can supply fonts, but FFmpeg’s current implementation only loads qualifying font attachments when filename metadata is present. Do not assume every attachment will be used automatically.
Correct ASS size or style after encoding and fonts
If characters decode correctly and the intended font is available, inspect the ASS script’s styles and intended video resolution. The filter’s original_size option supplies the original video dimensions used to scale fonts. Its force_style option can override subtitle style parameters. Check the script before changing either: forcing a style will not repair garbled text or make an unavailable font appear.
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Check shaping for Indic and other complex scripts
If the decoded characters are correct but their joining, ordering, or glyph forms look wrong, investigate script shaping and the libass capabilities in your build. A 2021 FFmpeg developer discussion describes auto, simple, and complex shaping modes and says auto chooses the best available libass shaper in that discussion. Treat those details as version-sensitive: check the filter help for your installed binary before using a shaping option.
Resolve subtitle paths that FFmpeg cannot open
Subtitle paths are parsed in two layers: first by the shell, then by FFmpeg’s filtergraph syntax. Shell quotes alone do not make every punctuation mark safe inside a filter expression. Commas, colons, brackets, quotes, and backslashes can require additional care. If FFmpeg cannot open the subtitle, try a simple path first; then add filtergraph escaping deliberately. A 2017 ffmpeg-user report documents a failure involving square brackets in a filename, but the exact behavior can depend on the command and environment.
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Troubleshooting by symptom
| Symptom | First check | Layer to investigate |
|---|---|---|
| Accented or non-Latin characters are garbled | Determine the subtitle file’s actual encoding and whether it is UTF-8 | Use charenc for confirmed non-UTF-8 text input |
| The wrong language or track appears | Inspect subtitle streams and indexes | Select the intended track with stream_index or si |
| The filter says only text subtitles are supported | Check whether the selected track is bitmap/image based | Choose a text track or use a workflow designed for bitmap subtitles |
| A font is replaced or glyphs are missing | Check the font family, installation, runtime visibility, and any font attachments | Font discovery and fontsdir |
| ASS font size differs from expectation | Check the source video dimensions and script resolution | original_size, then style options |
| Indic or other complex-script glyphs look wrong | Verify that characters decode correctly, then check shaping support | shaping and build capabilities |
| FFmpeg cannot open the subtitle despite shell quotes | Try a simple path and inspect punctuation in the filter expression | Shell quoting and filtergraph escaping |
Useful references
- FFmpeg filter documentation: subtitles filter
- FFmpeg subtitles-filter implementation
- 2021 FFmpeg developer discussion of subtitle shaping
- 2017 ffmpeg-user report about subtitle encoding and a path issue
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