SubFixr

SubFixr is a small command-line tool for fixing and cleaning subtitle files.

It's mainly for those moments when subtitles are slightly out of sync, or when you want to remove things like watermarks, ads, or unwanted lines quickly without opening a full editor.

It can shift SRT timestamps forward or backward, retime subtitles from one FPS to another, remove subtitle blocks by number, and drop blocks that contain matching text. If you have MKVToolNix installed, it can also extract subtitle tracks from .mks files or rebuild a new .mks after applying the same fixes.

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Requirements

• Python 3
• MKVToolNix on your PATH (only needed for .mks support)

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What it does

• Shift subtitle timing forward or backward
• Retime subtitles from one FPS to another
• Remove subtitle blocks by number or range
• Remove subtitle blocks that contain specific text
• Process a single file or a whole folder
• Walk subfolders with --recursive
• Write output next to the source file or to a custom path
• Rebuild .mks files while keeping subtitle track order, language tags, and track names

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Usage

python subfixr.py input [options]

You need to pass at least one of these:

• --shift
• --fps
• --remove
• --delete-lines

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Main options

• input Subtitle file (.srt or .mks) or a folder with subtitle files

• -s, --shift Shift amount like 1s, 500ms, 1min, or plain seconds like 1.5

• --fps Subtitle FPS retime in source:target or source target format like 25:23.976, 25 23.976, or 24000/1001:25

• -d, --direction forward / for or backward / back

• --delete-lines Subtitle block numbers or ranges like 1-8 or 1,3,5-7

• --remove Remove subtitle blocks that contain the given text

• -o, --output Output file or folder

• -r, --recursive Scan subfolders too when the input is a folder

• --overwrite Replace output files if they already exist

• --mks-output When the input is .mks, rebuild a new .mks instead of writing extracted .srt tracks

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Examples

Shift one file forward by one second:

python subfixr.py file.srt -s 1s -d for

Convert one subtitle from 25 FPS timing to 23.976 FPS timing:

python subfixr.py file.srt --fps 25:23.976

The same FPS change using two separate values:

python subfixr.py file.srt --fps 25 23.976

Shift every subtitle in a folder back by 500 ms:

python subfixr.py folder/ -s 500ms -d back

Process a folder recursively and write everything to another folder:

python subfixr.py folder/ -s 1min -d forward -o output_folder/ -r

Overwrite files if the destination already exists:

python subfixr.py temp/ -s 2.5s -d backward --overwrite

Remove subtitle blocks by number:

python subfixr.py file.srt --delete-lines 1-8

Remove a few blocks, then shift the rest:

python subfixr.py file.srt --delete-lines 1,3,10-15 -s 750ms -d back

Retime by FPS first, then add a small forward shift:

python subfixr.py file.srt --fps 24000/1001:25 -s 300ms -d for

Remove blocks that contain some text:

python subfixr.py file.srt --remove "viki"

Process a folder and remove matching text before shifting:

python subfixr.py folder/ --remove "viki.com" -s 1s -d for

Extract subtitle tracks from an .mks file and write them to a folder:

python subfixr.py file.mks -s 1s -d for -o output_folder/

Rebuild a cleaned .mks while keeping the original subtitle container layout:

python subfixr.py file.mks --remove "viki" --fps 25:23.976 --mks-output

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Order of operations

If you combine options, SubFixr runs them in this order:

1. --delete-lines
2. --remove
3. FPS retime
4. timestamp shift

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Notes

• Output defaults to a new file next to the source (usually with _synced added to the name)
• .mks support depends on mkvextract and mkvmerge being available on your system

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Small tip

If you're dealing with a lot of files, try running it on a folder with --recursive first and without --overwrite, just to see what gets generated. Once you're happy, run it again with overwrite enabled.