A free way to add simple sound edits without changing video quality?

[solkap]

I have a few MKV video clips in which I would like to have the sound fade out to silence over the course of 2-3 seconds at the end. I also have another MKV video clip in which I would like to add an approximately 30 second sound effect layer near the middle.

I've been playing around with VSDC Video Editor. The controls seem pretty straight forward, which is good, since I do have a rudimentary understanding of video editing, but not much beyond the basics.

However, I gather it is not a preferred piece of software around here. And it does seem to leave some noticeable compression artifacts after adding these effects. I believe they are "block boundary artifacts". The effect is similar to this example photo of a cat on Wikipedia, though it is much less pronounced in the video clips.

Is this a result of poorly adjusted settings when I import the MKV? Here's a screenshot of those import settings for an MKV titled "clip 2". As far as I can tell they match the original file's characteristics.

Or are there other settings somewhere else I might be overlooking or misunderstanding that I could adjust so the conversion is lossless?

Or is this one of the inherent limitations of this particular software?

In which case, does anyone have a suggestion for an alternative that is free? Or perhaps there is higher end editor that can accomplish this with a trial download that is fully functional (no watermark, no __ minute video length limit, etc.), even though it would be limited by time or number of operations?

Thanks in advance for any help!

[manono]

I expect VSDC Video Editor reencodes the video. Dunno for sure as I don't use it. So, to leave the video untouched, demux, work on the audio, remux.

The tools within MKVToolNix can do both.

[solkap]

Oooh, that's a good idea! Any suggestions for a good audio editing program that could handle the fading and layering of the demuxed audio streams, preferably free?

[solkap]

Perhaps Audacity would be capable of fading and layering audio?

[solkap]

OK, I was able to demux the MKV to a an H264 video track and a DTS audio track. Audacity doesn't seem to understand DTS, so I used the "convertio" site to convert the DTS to a WAV file, since my understanding is WAV is lossless and Audacity can handle it. I applyed the audio fade at the end, double checked that the length of the faded sound clip was the same as the original, converted the WAV back to a DTS on convertio, and used MKVToolNix to mux them back together.

But the resulting clip has audio that is out of sync.

I determined that the audio was lagging about half a second behind the video using VLC and I tried to fix this with Avidemux, all using the method described here.

The result would be great, except it seems to push off about a half second of audio at the end, cutting into the end of the fade.

Do I need to re-edit the sound track again to push the fade back another half second to compensate? Or is there something I'm missing in the remuxing process that could be causing the misalignment?

[davexnet]

Take the DTS audio from the convertto site and load it with the video in MKVtoolnix.
Highlight the audio and fix the delay right there, on the right, timestamps and duration/delay

[solkap]

That worked perfectly! Good grief, I'm not sure if it could have been any more obvious!

Thanks for the info and the patience!