Subtitle Composer
Subtitle Composer is an open-source KDE subtitle editor for SRT, SSA and ASS text subtitles, waveform timing, video preview, format conversion and error checks.
What it is for
Subtitle Composer combines a video preview, timeline and audio waveform for editing, timing and converting common text subtitle formats. It supports checks for overlaps and gaps, splitting and merging, spelling review and selected recognition or OCR workflows. A plain editor is enough for a few text changes, while the timeline is more dependable for a full synchronization pass.
Format and backend boundaries
SRT, SSA, ASS and other formats carry different style, positioning and effect information. Conversion can discard those details. Linux packages may expose different codec, FFmpeg, model and file-access behavior, so compare package types when a sandbox build cannot read a stream or external model.
Recognition needs review
Speech recognition, OCR, encoding detection and timing checks reduce repetitive work but do not guarantee correct words or timecodes. Noise, multiple speakers, proper names, low-resolution captions and variable frame rates can all produce errors. Keep the original subtitle and a reviewed delivery copy.
Maintenance note
This page was reviewed on 2026-08-23 against the 0.8.2 Linux package metadata, format notes and GPL-2.0 licensing information. The package and codec support should be tested with a short sample before a full project.
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Subtitle Composer installation and synchronization workflow
Install the Linux package, load a copied video and subtitle file, align a short section on the waveform and export a reviewed copy.
Before you start
- Use Linux and choose an AppImage, Flatpak or distribution package that matches the system.
- Prepare a playable test video and an SRT or ASS copy; keep the original subtitle untouched.
- If recognition or special codecs are needed, check that the package can access FFmpeg, models and the required permissions.
Installation steps
- 01
Install or run the selected package
Give an AppImage execute permission, or install a Flatpak or distribution package through its package manager. Do not mix native packages from unrelated distributions.
- 02
Test video and audio access
Load a short test video and confirm picture, sound and waveform access. If a sandbox package lacks a codec, compare another package type before changing the source file.
- 03
Configure autosave and language
Set the interface language, spell checking and autosave behavior, then confirm the default project and export directories.
Quick start
- 01
Open copies of the video and subtitle
Load the video and copied subtitle, then verify frame rate, start time and character encoding before editing.
- 02
Align one section on the waveform
Locate a clear dialogue start, adjust the selected subtitle start and end times, and preview a short section before applying a wider offset.
- 03
Check and export the target format
Run overlap, duration and blank checks, preview key sections and save another file. SRT cannot retain every ASS style detail.
Usage tips
- Use several synchronization anchors for a long video instead of correcting only the first line.
- Treat OCR and recognition output as a draft and verify names, punctuation, speakers and timecodes manually.
- Open unknown subtitles as text first and check encoding before allowing scripts or overwriting the source.
Troubleshooting and uninstall
Why is there no waveform even though the video plays?
Check the selected audio stream, FFmpeg support and cache permissions. A sandbox package may lack a codec; compare an AppImage or distribution package with the same sample.
Why are the subtitles garbled?
Reopen the file with the correct encoding and save a UTF-8 copy after checking the result. Do not overwrite the original before the text is confirmed.
- Export subtitles and project filesSave the project, subtitle copies, scripts and dictionaries in a separate directory and verify that all changes are complete.
- Remove the package by its installation methodUninstall a Flatpak or distribution package through its manager; remove an AppImage file directly. Clear configuration and caches only after checking their contents.
Frequently asked questions
Is Subtitle Composer available for Windows?
The current package information is organized around Linux, and a current Windows build may not be available. Treat older Windows packages as compatibility archives until verified.
Can it turn speech directly into subtitles?
Recognition and subtitle extraction can be available, but results depend on models, FFmpeg, codecs and package permissions. Always review the generated text and timing.
Which formats can be edited?
Common text formats include SRT and SSA or ASS, with other formats depending on the build. Check style and positioning support before converting a styled subtitle.
What should be preserved before export?
Keep the original file, a reviewed working copy, the frame-rate assumption and the final exported format so a later correction can be traced.