Switch video dts file with ac3 file

[tfamok]

Hi everyone, I hope you are well.
I have an mkv video which has good quality dts audio. After converting to dvd and playing on my tv I now realise my tv is not capable of playing dts audio. In the same folder as the mkv video/dts audio is another folder called 'External AC3 audio'. I thought great, I can just switch the dts audio in the video with the external ac3 file. Simples.
Unfortunately, it wasn't simples. It was very unsimples and I'm stuck. I couldn't find a lightweight way that didn't require 3 bits of software etc to be installed. Audio is way above my head and thus, having failed all other avenues, I thought I would ask some knowledgeable people for some help.
Is there a way to just do the old switcharoo? At the minute I'm just converting the dts into ac3 using mkv audioconverter but this seems silly seeing as how I have a separate ac3 file waiting to be used.
Thank you for reading my post smart people.
Kind regards,
Teddy

[pandy]

You can mux external audio with ffmpeg - at same time you can keep DTS or not purely up to you.

Bellow example (not tested - written ad hoc) copy video from first file and audio from second file - should work OK

ffmpeg -i "video source" -i "audio source" -map 0:v -c:v copy -map 1:a -c:a copy -f matroska "new file with video and external audio"

To keep original audio (DTS) with additional audio track something like script bellow can be used (same as above - not tested)

ffmpeg -i "video source" -i "audio source" -map 0 -c copy -map 1:a -c:a copy -f matroska "new file with video, audio and external audio"

[tfamok]

Bloody hell pandy wasn't expecting to have to write code lol
Your advice is much appreciated actually. I'm guessing this is the easy standard for morons like myself. Will give it a try.
Thank you

[sneaker]

You can also use MKVToolNixGUI. Drag&drop both mkv and ac3 file, un-tick the DTS track (or not if you want to keep it) and click "Start multiplexing".

Since pandy already started showing ffmpeg commands I will add one more for converting dts to ac3 (in case you don't have any extra ac3 file in the future):

ffmpeg -i "video source with dts " -map 0 -c:v copy -c:a ac3 -f matroska "new file with video and ac3 audio"

[tfamok]

Thank u sneaker. Very valuable info. Gonna try same video with different audio methods.
Cheers guys.

[pandy]

Or perhaps it will be nice to keep original HQ audiotrack but add new AC-3 side to it.

Bellow tested example

@ffmpeg -i "%1" -map 0 -c copy -map 0:a -c:a:1 ac3 -b:a:1 448k -f matroska "%~n1_newaudio.mkv"