MKVMerge batch file script help - replace default audio track?

[Valnar]

Calling all experts!

I am in need of a Windows batch script to help with a project. Normally even ChatGPT can help, but it's failing on this one.

I have a directly full of MKV files with one or two audio tracks. The first audio track is the default in every file. I want to replace that audio track with a separate .ac3 file, set it to English, and (re)make it the default. Where my scripting mojo messes up is I can't figure out how to accommodate the fact that some of those files have two audio tracks already, and I don't want the second one touched (nor any subtitles, chapters, etc).

Most of my attempts seem that MKVMerge wants to know the overall track order, which can be different between MKV files. ie. --track-order 0:0,1:0,0:2,0:3 (or 0:4, etc). Is there a way I can make it blindly just replace that first audio track without having to know anything about the rest of it?

I'm okay with doing this in FFMPEG too if it makes it easier, but all previous attempts were just as unsuccessful.

[Gromyko]

https://video.stackexchange.com/questions/19634/mux-mkv-and-dts-file-change-default-audio-stream-and-language


https://video.stackexchange.com/questions/29467/change-default-audio-track-of-video-file-using-ffmpeg

[Valnar]

That didn't help me unfortuantely.

[pcspeak]

The following lines of code do NOT replace any audio streams. The new stream is added to the mkv.
I could not work out how to consistently replace the old stream without breaking something. I figure it's better to just add the new audio as the first audio stream, and make it the default.

I've added a wav file to the mkv.

@echo off
if not exist New\ md New
for %%a in (*.mkv) do ffmpeg.exe -i "%%a" -i "%%~na.wav" -map 0:v:0 -map 1:a:0 -disposition:a:1 none -disposition:a:0 default ^
    -map 0:a -map 0:s -metadata:s:s:0 language=eng -disposition:s:0 forced ^
    -c copy -y "New\%%a"
 pause

I don't have many files to do a thorough test. ymmv.
Cheers.

[Valnar]

I'll check it out. thanks