h.264/AAC.MKV not compliant?

Lightworks and Resolve support h.264/AAC.MKV for quite a while. It works quite robustly, usually.

Some files created with VAI show audio issues in both applications. I created two test clips for you to test with, downloadable here.

In Resolve 18.6, both clips show audio tracks, but no sound. In Lightworks 2023.2, they shows wave forms of wrong duration and partially distorted sound in the second half of the timeline. The clips have been created with the settings shown below ( 59.95 fps and 50 fps, the rest untouched):


Download link is not working for me to test those clips.

Sorry, seems that something went wrong, but I don’t know what.

Try this: DVD Master MKV.rar - pCloud

I see now that there’s something wrong with my cloud service. Some files are downloadable others throw an error message when trying to download, weird. In the meantime, I uploaded a copy to Wetransfer.

Apologies for the inconvenience and thanks for investigating the issue.

Any new on this?

In the meantime, I raised the issue with Lightworks. They are investigating. I’m waiting for response. Didn’t raise it with Resolve, yet.

Wondering why some MKV files created with TVAI work as expected in Lightworks and Resolve, but others show audio issues?

Have you found the cause and, most important, is it fixable in short terms?

I am still trying to figure out what is going on with the files. I have audio with them in VLC Player, although it looks slightly off on the 50fps at times, but nothing plays in Resolve. Do you have the original video file that was unaltered by Video AI?

My best guess is that the duplicate frame detection and frame generation introduce issues with timestamps.

Yes, I have the original. It’s one of my standard test clips for SD conversion, nothing exotic. Here you go:

I’ve Got The Clap.zip (5.2 MB)

Any news on this?

Now, that you have all the media to reproduce the issue, could you figure out what it is caused by and, most important, is it fixable in short terms?

Niko, I just tested this export again out of Video AI and then pulled it into Resolve and I have the audio tracks in the MKV file format after processing. When I originally tested it I was able to recreate the issue in Resolve but now it is working. I am in Resolve 18.6.5 build 7

Lucky you. I’m on Resolve Studio 18.6.5 build 6 and will update to the current release, which is 18.6.6. soon.


However, my main NLE isn’t Resolve, but Lightworks. Have you had a chance to look into Lightworks as well?

Sad to say, but based on my findings, which I’ve reported here and in another thread recently, my impression is that MKV written by TVAI has not one, but many issues.

FYI to test the shared files with Lightworks, you don’t need to purchase a license. They offer a free version, which is sufficient for the purpose. To download the installer, you need to register with them - that’s all, no obligations.

Ok, I installed the latest release of Resolve on Windows, which is 18.6.6 build 7 and I see that the shared clips come in as Video+Audio, but there is still no sound. Please crosscheck your findings.

To illustrate what I see and hear, I made this screen recording:

By the way, why doesn’t the forum software allow attaching short videos, like the one above?

Niko, I ran it again and I am getting audio playback in Resolve.

That you could reproduce the problem earlier and now you can’t is a disaster for me, becasue the problem on my side persists. What is your conclusion?

And, very important to me, what is with Lightworks?

Just to say, I noted in the other thread that I’ve already rendered over 400 MKV clips. That wasn’t a joke. The total video duration of those clips is around 150 hours, which gives on my machine around 300 hours of rendering time. That was prior to detecting the issues.

I just installed Lightworks and the clips did play with audio when brought in. Not sure what this means on your end if you are still seeing the issue with the exported clip. Is it happening everytime now?

I really appreciate that you are testing the clips in Lightworks.

There are two issue.

  1. The waveform is wrong. It should span the full duration of the audio, but as you can see in your screenshot it ends close to the middle of the sequence. A closer look heavily zoomed-in (Ctrl+mouse-wheel), will reveal that the waveform doesn’t match the audible sound.

  2. The sound is partially distorted. Start playback after the waveform ends in the timeline to hear it.

I’ve never seen something like this before, so I have no good guess what can cause such a problem.

I shared the clips with the Lightworks developers as well. If your devs want to contact the Lightworks devs for cooperation to find the cause(s) to solve this problem, you can use their form “report a problem” for the first contact.