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, 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.

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

• Shift subtitle timing forward or backward
• 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

python subfixr.py input [options]

You need to pass at least one of these:

• --shift
• --remove
• --delete-lines

• 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

• -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

Shift one file forward by one second:

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

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

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" --mks-output

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

1. --delete-lines
2. --remove
3. timestamp shift

• 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

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.