Avidemux Forum

As we all know, Avidemux is the best tool ever for easy and laser sharp cutting of MKV files. It's dead simple to use and does an excellent job of cutting. For years and years and years, I've been looking for a program that was as good as Avidemux with cutting -BUT- was able to retain/re-index SRT embedded subtitles.

I tried lots of MKV editors and Clever FFmpeg-GUI was the closet to what I needed but it's GUI (for whatever reason) seems backwards to me, it made my head hurt using it. I eventually gave up on my quest and forgot all about this journey ... until yesterday.

I had my brother use Claude to generate some helper files that would let you save your project file after cutting a video and take that .py file, the original MKV and the saved/cut MKV and would do some AI magic and presto chango, spit out a finished MKV, WITH SUBS, that are perfectly in sync with all the cuts you did!

I don't know if I'm allowed to post it here but if I can, I'll gladly share it with the world. To me, this makes Avidemux 1000x better.

Loving AI for stuff like this! My brother, nor myself, are developers but I'm really good at writing prompts.

I would be interested in seeing the steps you use to get AI making subs.

I use https://sourceforge.net/projects/subtitle-workshop-classic/ which offers a lot of options but is complex to get use to it.  You can move timeings by just seeing the audio waveform which is often good for spotting start of dialog.  You also get warnings when the number of words exceed maximum average reading speed. It's easier to let some long sub lines extend into silence and it's easy to spot when the scene changes.  However, of course this is a lot of work to make a high quality subtitle or fix an existing one. I've noticed that a lot of .ass files fail to load because they are missing a leading 0. in the timing on each line.  Maybe the new version is better. Such .ass files can be fairly easily fixed with a text editor search replace.

I don't understand why you want to edit media that has srt subs.  Are you just removing ads?  I can see why removing a brand promo at the start can require a timing change for every sub, but you can do that pretty easily at: https://subtitletools.com/subtitle-sync-shifter
I use that all the time to fix timings.

Quote from: roadhazard on October 28, 2026, 01:11:00 AMI don't know if I'm allowed to post it here but if I can, I'll gladly share it with the world. To me, this makes Avidemux 1000x better.

If you're not posting links to alternatives to Avidemux (bad form), and there are no potential licensing issues with anything you post, it really should not be an issue.

Quote from: sark on October 30, 2026, 10:58:49 AM

Quote from: roadhazard on October 28, 2026, 01:11:00 AMI don't know if I'm allowed to post it here but if I can, I'll gladly share it with the world. To me, this makes Avidemux 1000x better.

If you're not posting links to alternatives to Avidemux (bad form), and there are no potential licensing issues with anything you post, it really should not be an issue.

Where would I post it? Can I add a link to my Proton drive on here?

eumagga who moderates here generally recommends We Transfer, Dropbox, Mega or Google Drive. I'm assuming Proton Drive is a similar alternative and accessable to all, if so, I cannot see a reason not to use it if that is your prefered choice.

Quote from: alexstorm on October 28, 2026, 08:39:49 PMI would be interested in seeing the steps you use to get AI making subs.
...snip...

I asked ChatGPT to type up everything my brother and I did and here you go (wall of text warning)

How I Added Automatic Subtitle Preservation to Avidemux Using Claude Code and Codex

I thought I'd explain how this project evolved, because it wasn't simply a case of giving Codex a single prompt and having it create everything from scratch.

The original subtitle-repair utility was developed using **Claude Code**. Later, I used **ChatGPT to help formulate the instructions for Codex**, which integrated the existing utilities into Avidemux and eventually compiled working Linux and Windows versions.

1. The original Claude Code project — avisubfix

The original problem was that Avidemux discards embedded subtitle tracks when saving an edited MKV.

I wanted to be able to remove unwanted scenes from a movie or TV episode, save it using Video Copy and Audio Copy, and retain the original subtitles with their timing corrected automatically.

Claude Code initially developed a standalone Python utility called `avisubfix.py`.

It was designed to:

- Read an Avidemux project file (`.py`) to determine exactly which sections of the original video were retained.
- Interpret Avidemux's `loadVideo`, `appendVideo`, `addSegment`, and marker information.
- Extract subtitle tracks from the original MKV using MKVToolNix.
- Remove subtitle events belonging to deleted portions of the video.
- Adjust subtitle timestamps to match the new, shorter timeline.
- Trim subtitle events that overlap cut boundaries.
- Preserve subtitle track languages, names, ASS styling, and supported font attachments.
- Handle SRT, ASS/SSA, WebVTT, and PGS subtitles, with some VobSub support.
- Preserve and adjust chapter information.
- Remux the corrected subtitles together with Avidemux's edited video/audio using MKVToolNix, without re-encoding the video or audio.

The standalone utility could be run manually after saving a project and edited MKV.

For example:

`python avisubfix.py --project cut.py --edited cut.mkv`

This created a separate corrected MKV containing the edited video, audio, and restored subtitle tracks.

The subtitle-repair logic itself was independent of Avidemux's GUI.

2. Turning the standalone tool into an automatic Avidemux feature

The next goal was to eliminate the need to save an Avidemux project and manually run a Python command after every edit.

Using Codex, we developed an integration that connected the existing subtitle-repair engine to Avidemux's native save process.

The resulting helper system consists of three principal Python files:

**`avisubfix.py`**

The original subtitle-processing engine. It contains the logic for interpreting video cuts, extracting subtitles, correcting timing, and rebuilding the MKV.

**`avisubfix_integration.py`**

Handles the automatic post-save workflow. Instead of requiring a separately saved Avidemux project, it uses a manifest generated by the modified Avidemux save code. This manifest identifies the original source files, retained segments, source timestamps, and output timeline positions.

It also handles timing details such as source timestamp offsets and B-frame timing, which are important for accurate synchronization.

**`avisubfix_autorun.py`**

Supervises the background subtitle job. It launches the processing engine, handles the required external utilities, and allows subtitle processing to continue independently of the Avidemux GUI.

Codex also modified Avidemux's C++ save path so that, after the edited MKV has been successfully saved and closed, Avidemux can generate the required information and launch the subtitle helper automatically.

The workflow is now:

1. Open an MKV in Avidemux.
2. Make the desired cuts.
3. Select Video Copy, Audio Copy, and MKV output.
4. Save the edited file normally.
5. Avidemux launches the subtitle-restoration process in the background.
6. The helper creates a second file named `filename.subs.mkv` containing the edited video/audio and corrected subtitles.

The original edited file remains untouched. The second MKV is the subtitle-restored version.

There is no need to manually save a project, run Python, or open another program. The background worker can also finish after Avidemux has been closed.

3. First successful Avidemux integration — 2.8.1 Qt5

We initially had problems with newer Avidemux builds stuttering when pressing Up Arrow to seek between keyframes during active playback.

The older Avidemux 2.8.1 Qt5 release worked correctly.

Codex therefore integrated our subtitle tools into Avidemux 2.8.1 Qt5 and produced:

- A Linux AppImage.
- A Windows x64 portable version.

Both were successfully tested, including subtitle synchronization and automatic background processing.

That established a working reference implementation.

4. Moving to Avidemux 2.8.2 and Qt6

After the developer posted a fix for the playback seeking regression, I decided to try compiling everything again using the newer Avidemux 2.8.2 development source and Qt6.

The upstream seeking fix was:

https://github.com/mean00/avidemux2/commit/e054b7985521f78fd44d2ca932af6f0cc01fa2dc

I asked ChatGPT to prepare a detailed Codex prompt using our existing working subtitle project as the starting point.

Here is the opening of the actual prompt:

> I want you to build a new experimental version of Avidemux using the latest available Avidemux 2.8.2 development source, Qt6, the recently released upstream playback stuttering fix, and our previously completed custom subtitle-preservation modifications.
>
> Important: Skip ALL testing. Your job is to integrate, compile, and package the software only.

The rest of the prompt instructed Codex to:

- Reuse the existing working subtitle implementation rather than rewrite it.
- Use the Avidemux 2.8.2 development source.
- Verify that upstream commit `e054b798` was included.
- Use Qt6 exclusively, with no fallback to Qt5.
- Preserve the complete SRT, ASS, PGS, chapter, and background-processing functionality.
- Adapt the integration to any changes in the 2.8.2 source.
- Compile a Debian 13 Linux AppImage.
- Compile a Windows x64 portable version.
- Bundle the necessary helper utilities and runtime dependencies.
- Keep the existing working 2.8.1 builds untouched.
- Skip automated and manual runtime testing, since I would test the final builds myself.

The exact Avidemux source revision Codex selected was:

`c7e6576d605de685fae0b126204e4258aa92026d`

That revision already incorporated the upstream seeking fix.

5. Linux Qt6 build

Codex successfully compiled and packaged Avidemux 2.8.2 using Qt 6.8.2 on Debian 13.

It included our C++ subtitle-save modifications and Python helper utilities.

I personally tested the finished AppImage.

Both major requirements worked:

- Up Arrow seeking during active playback no longer stuttered.
- Saving an edited MKV automatically produced a correctly synchronized `.subs.mkv` file.

6. Windows Qt6 build

The Windows build required additional work because our earlier cross-compilation environment used GCC 5.5 and Qt5.

Codex established a newer native Windows build environment using:

- MSYS2 UCRT64
- GCC 16.2.0
- MinGW-w64 14.0.0
- Qt 6.12.0

It compiled Avidemux and packaged the portable Windows application with the subtitle utilities, Python, MKVToolNix, and the necessary runtime libraries.

The first Windows Qt6 build successfully saved edited videos but failed to generate the `.subs.mkv` file.

Rather than blindly modifying the code, I instructed Codex to compare the working Windows 2.8.1 implementation, working Linux 2.8.2 implementation, and failing Windows 2.8.2 implementation.

Codex identified a specific problem:

The Windows launcher supplied a `--mkvtoolnix-dir` argument, but the bundled `avisubfix_autorun.py` supervisor did not recognize it. Python's argument parser exited before subtitle processing began.

Codex restored the missing argument handling and rebuilt the Windows package.

The corrected **Windows Fix1 build now works properly**, including automatic subtitle restoration.

7. Final results

As of November 6, 2026, I have personally confirmed that both versions work:

**Linux:** Avidemux 2.8.2 development + Qt 6.8.2 + upstream seeking fix + custom subtitle preservation.

**Windows:** Avidemux 2.8.2 development + Qt 6.12.0 + upstream seeking fix + custom subtitle preservation.

Both support smooth keyframe navigation during playback and automatic generation of subtitle-restored MKV files.

The original 2.8.1 Qt5 builds have been retained as backups.

Final thoughts

I want to emphasize that this isn't an official Avidemux feature or a simple Python script dropped into an unmodified Avidemux installation.

The solution combines modifications to Avidemux's C++ save process, a Python subtitle-processing engine, a background supervisor, and external MKVToolNix utilities.

Claude Code provided the initial standalone subtitle-repair solution. Codex was used to integrate the utilities, adapt the C++ code, port the implementation between Avidemux versions, and compile/package the custom builds. ChatGPT helped formulate the detailed implementation and troubleshooting prompts.

The important part was having an existing working implementation for Codex to reuse, rather than asking it to invent the entire solution in one pass.

For my MKV editing workflow, the result has been exactly what I wanted: I can cut video in Avidemux without re-encoding, and the subtitle-preservation process runs automatically afterward.